Wood (construction material)

This article treats Bois like construction material . It exposes the advantages and the limits of them. More than one collection of definitions, he wants to be collection of knowledge, sometimes almost lost. The text is long, it is possible to pass directly in the chapter practical advices!

Definitions

• construction calls upon the duramen; perfect wood or of heart (which constitutes the central part of the Arbre); more durable than sapwood.
• the Aubier, often more clearly and light that the duramen, consists of alive cell S. it is more easily and quickly attacked by the insects, bacteria and mushrooms.
• the Cambium is the fine zone separating the sapwood of the bark, which produces wood, generally not used.
• the bark is sometimes traditionally used; Plates of bark of Birch unrolled, support for example the lumps of earth of the vegetalized Toitures of the Scandinavian countries.

• the directions of cut modifies the aspect and the technical quality of timber sawn. It is:

• longitudinal: parallel with the veins of wood, therefore vertical for a tree on foot.
• radial: heart towards outside.
• tangential: ± parallel with the rings of growth of wood.
• the timber end grained is cut perpendicular to the longitudinal direction,
• wood lying is cut the longitudinal direction parallel to,
• “on district”: split in the radial direction before being crossed in the longitudinal direction,
• “on slabbing off-cut”: half-compartment in the longitudinal direction.

Constructive aspects

Solid and light material

The spruce for example has a density ranging between 430 and 470 kg/m ³ when it is dry with the air (water content of wood 15%), that is to say five times less than the Béton and seventeen times less than the Acier. A house of two floors and 100m ² on the ground built out of hard materials will thus weigh 200 tons, against 70 tons in “bone”. The resistance of wood compared to its weight makes it very gravitational for light achievements. Moreover, wood deadens the shocks.

Wood is very resistant to the Compression and the traction, in its direction longitudinal, and rather resistant to the transverse inflection (especially in lamellate-stuck). But if it does not break, it folds if the section of parts subjected to the inflection (principal rafter S, Poutre S)) is insufficient. In compression, the problem of the buckling, related to the flexibility of wood, must be solved by a relatively small height-width ratio. The resistance of wood to compression is high. For an equal resistance, wood requires a section larger than steel or the concrete.

Insulating material

The thermal Conductivity of the spruce, for example, is of λ = 0.11 W/m°C: fifteen times weaker than that of the concrete and four hundred times weaker than that of steel. Wood are “subjectively hot”, because the thermal Effusivité of wood is low (EFF = 0.56). A building with Ossature wood is heated easily. The air is dry and healthy there, thanks to wood and with insulator easily placed between the amounts of the framework. The temperature of the walls is close to that of the ambient air, which increases thermal comfort. The cold bridges are limited. On the other hand, wood accumulates heat little; its Heat capacity is average (S = 1500 kJ/m ³). It does not have a “thermal wheel of inertia”, but can be associated with an accumulating mass (S > 1900 kJ/m ³) in the center with the building, (stone chimney or earthenware stove for example).

- In cold countries, wood is very appreciated for qualities quoted above.

- In hot countries, it is less pleasant than the stone because accumulating the freshness of the night badly.

Le wood is Porous, because constituted of network of Fiber S and vessels, directed longitudinally, which explains why - whatever is the gasoline, he has a larger thermal conductivity (thus a less capacity insulating) in the direction of its veins than in the perpendicular direction; the grounds in wood paving stones “ upright ” are fresher than those, of the same wood, identical thickness, in boards lying or parquet blocks.

See also: Insulator

Chemically resistant material

Certain gasolines have a resistance raised to the Corrosion, supporting the chemical aggressions well, better than the concrete or current steel. It for that is readily used in certain factories where the atmosphere is aggressive. Wood like the Teak, the afzélia doussié, are used for the manufacture of tanks containing certain chemicals. The spruce is regularly used for the salt silos along the highways.
Certaines wood turpentines has chemical compounds which interact with iron (Western Red Cedar, Merbau, Afzélia, Chêne, Pin of Oregon…). To avoid spots and/or a corrosion of the nails and screw used to fix them, those must be in Stainless steel.

Hygroscopic and anisotropic material

Wood undergoes a drying shrinkage and a swelling with the temperature and especially the relative Humidité of the air or the contact with water. The withdrawal and/or swelling are larger in the tangential direction than in the direction Radial E. It is less in the direction Longitudinal but considerable, in particular in the construction industries made up of wood posts being neighborly of the masonry walls (staircase…). These various withdrawals according to the direction considered can cause tensions in wood. The wood of reduced section will warp, while the wood of strong section (beams, roundwood) are likely to be split during a too fast drying. In the wood of strong section particularly, this can be accentuated by an unequal withdrawal, following the faster drying of the ends, having for consequence of the slits of wood upright. The drying of the ends is slowed down by covering them with a wax or a water repellent (fills in, lasure…). The parts of strong section must be stored with the shelter of the sun and the drafts to slow down drying, each gasoline of it having in addition a different behavior.

See Perenniality of wood for a table taking again the various shrinkings of the wood of the green state in dry state a “with the air” (12% of moisture), and a table presenting the movement of wood compared to the relative humidity of the air.

not to confuse withdrawal and movement :

• the withdrawal is due to the wood seasoning since the state coldly cut until the dry state.
• the movement is due to the variations of relative humidity of the air, and this after drying and setting works.

The gasolines with high movement should be used on district, the withdrawal being less in this direction than on slabbing off-cut. Wood must be used with a water content compatible with its use, especially the species which have a raised withdrawal, to limit the risk of deformations due to the movement. “defects of growth” of the tree can also generate wood of reaction, which différentiellement becomes deformed normal wood in the longitudinal direction, and less in the two other directions, generating internal stresses (which can interest certain carpenters).
Le level of moisture of balance of wood is reached after a certain time, following the variations of moisture of the air. Especially in the case of the wood of strong section, the extreme values will never be reached, and the movement will be less important. The parts in contact with intermittent moisture must nevertheless be assembled so as to allow their movement.

Material adapted on the difficult ground

By its lightness and its flexibility, wood is adapted on the slopes, ground of weak Portance, Pergélisol S, zones of seismicity. The Affaissement S on the one hand weaker, on the other hand are absorbed without visible consequences (cracks) by the timber structures. the costs of foundations of new constructions are reduced, especially on the difficult grounds or inclined. The extensions, field particular of architecture often generating disorders which had with the compressing of the new construction, are often made out of wood, the weak weight of the structure involving a less compressing and thus less risks of cracks or wrenchings.
Dans the countries with strong seismicity, wood is often preferred for its capacity to absorb the seismic shocks instead of transmitting them. In Japan, the assemblies at edges are rounded for even more flexibility.

Biodegradable material

Wood not protected is naturally bio-range by associations of insects Xylophage S, Champignon S and bacteria, and little by little eroded by the wind, the dryness, the solar Ultraviolet S. The best way of building to preserve wood varies according to the area. In moderate zone wood must be able to breathe, certain gasolines must be protected from the contact with the rain or the ground. Many gasolines resist a long time in total immersion (not of mushroom attack), or a momentary moisture (tiles of Châtaignier, spoon of kitchen out of boxwood wood). In fact especially the confined wet atmospheres or the stagnant water respectively support mushrooms and the bacteria, which prepare the work of the insects Xylophage S.
La poses convenient vapor barrier, a suitable fungicidal treatment can slow down the rotting of a piece of wood in permanent contact with the air and moisture; the kind and the source of the wood determine its lifespan (a French birch will be degraded quickly, where a birch of Siberia whose growth was twice slower will resist. The stakes of grazing ground in oak or better, in acacia are very resistant, with a weak point: not the buried part, but the collet, with the short-nap cloth of the ground.
the Pesticide S (Insecticidal S and Fongicide S are used more and more, not without Risque for the health of the users, and the Environnement, and with problems for the recycling of wood and of its waste in construction. (the sawdusts or dust of sandpaperings of unquestionable wood treated can be violently Toxique S.

Simplicity of implementation

Wood lends itself to the Autoconstruction, with the Préfabrication, the Artisanat as with the industry. The system with framework is very flexible, the woodens building are easy to transform and increase. The methods of assembly are numerous and adapt to all the situations, of simple the Clouage with the very powerful Collage, while passing by the Broche S, Plaque S, Boulon S, etc

Material resistant to fire

Wood resists the Incendie better that other materials. When the reinforcements of the Reinforced concrete become deformed and make rock the structure, sawn timber burns only of 0,7 mm per minute (4,2 cm per hour) and carbonized form lays down it a protection for the heart of wood. It dilates only little and the structure remains stable, even if the fire lasts a long time. Lastly, the statistics show that the fire hazard is not higher for the houses out of wooden than for the “traditional” houses. Moreover firemen have habit to say that wood has " the elegance of prévenir" before yielding, it cracks, contrary to a metal framework, which leaves them time to leave.

Durable material

As long as the roof is well maintained, the wood houses are remarkably stable (factor of durability), often more than of the houses of brick S or concrete. Many dwellings with Half-timbering going back to 1750 (in particular in the area of Malmedy, Stavelot…), in Belgium, are still inhabited and in very good state. Some firm of the Country of Herve date from the end of the 16th century. France has some of them, in particular in Brittany, Normandy and Alsace. In Scandinavia, Slovakia and Poland, a certain number of church S out of wood, without any important restoration, have existed for 600 years. Old Egypt gave us many Meuble S and a solar Barque in a perfect state of conservation (approximately 2500 years). Boats run at sea, rest centuries since there; recently, a boat at summer discovered in the Somme (approximately 900 years). Their wood would be degraded however now quickly with the air. The foundations out of wooden of a Roman Voie still remain under a modern road in the Belgian Fagnes (area of Malmedy). Venice survives the attack repeated of the sea on its wood piles.

Ecological aspects

Wood is a natural material, having consumed little energy and to a certain extent, renewable. If it is about an indigenous wood, he consumed energy for his transport little, and its waste can be recycled on the spot.
L' tree, while pushing absorbs CO₂ and releases from the oxygen. In tropical zone, while dying it undergoes a biological degradation by the Insecte S, bacteria and mushrooms which use oxygen and release a quantity equal of CO₂ to that absorptive by the tree lasting its growth. The assessment is then known as “neutral” (with at least an exception; the Terra lent). In moderate Zone, the forest Humus (if the forest is not destroyed or is not overexploited) or some Tourbe S accumulates part of this carbon (Puits of carbon). On the other hand, if one cuts the tree to maturity and that one prevents it from degrading oneself by using it in the construction industry, the carbonic gas remains stored. There is thus less CO₂ in the atmosphere and this contributes to reduce the Greenhouse effect.

The use of wood requires little matter and energy, and this in all the stages of a construction: manufacture is done naturally, the transformation is weak, the implementation requires few additional products and remains generally easy. The pollution of the physical environments (Air, ground, Water) is very weak, and waste can sometimes be recycled in other construction industries or burned to produce energy.

The consumption of gray energy for the production of structural timber (local wood, sawn, planed, ready with employment) is of 300 K W H/ton, against 450 for traditional masonries in Terra cotta, 8000 for the Acier, 250 to 300 for the ordinary Béton (!), and from 100 to 1000 for the stone, according to the degree of completion.

the panels ; The Recyclage of the by-products of wood is a good thing, but it is necessary to pay attention to the Colle S used which can, they, being polluting.

The presence of toxic chemicals (Pigment S containing Siccative Heavy metals, containing Lead, Adhesive S, Wax S, Varnished, Fungicidal S and Insecticidal S, Painting S, etc), or of remainders of nails and screw makes its recycling delicate, but not less than that of a plate of Plâtre, whose layers are not easily separable. Even flaring, an element of treated wood will release less Gaz with greenhouse effect and of Pollution that the only production of heat for the recasting of a steel element.

Comfort

The materials which surround us have on us a physiological impact considerable. Natural wood is very positive in this field:

• wood is hygroscopic. With the proviso of not being covered with a film forming completion, it partly controls the production of Steam by the inhabitants. Indeed, when there is too much moisture, the wood, which has a great hygroscopic capacity, absorbs this excess for the retransmettre with its environment when the circumstances require it. This is very pleasant because lack of moisture (generated by the central heating) supports ignitions of tracts respiratory, presence of Germ S pathogenic in air, increase of loads electrostatic…, while an excess of moisture disturbs the heat transfers between the body and its environment, sensitizes the Cornée, decreases the Electrical resistance of Peau, which increases the risk of electrocution with defective electricals appliance, etc

• natural wood does not contain harmful substances and does not produce any in the event of fire. But certain pesticides, container of the harmful substances, are dangerous both for the health of the inhabitants the environment. The products can be released in the form of Gaz in the interior atmosphere, be diluted by the rain and pollute the rivers, or be transformed into dangerous smoke when it is burned. It is thus advisable to be attentive with the nature of these products.

(fine dust of unquestionable wood (e.g.: kambala, iroko, oak…) are harmful.

• wood is less radioactive of all construction materials.

Thanks to implementation the dry, timber constructions have a healthy atmosphere and a capacity isolating as of the end from the building site, contrary to the processes of construction per wet process, which spend several months to be dried, prohibiting the implementation of the completions, producing a wet, cold and unpleasant atmosphere.

On the other hand, wood is poor a phonic insulator. It cannot oppose of important mass to the transmission of the airborne noises. One corrects this defect by adding insulating materials in the composition of the wall. Nevertheless, wood absorbs the sounds and it is used to fulfill the requirements of the concert halls.

The rise of the oil price and the Energy crisis which was followed from there contributed to bring among people a reflex of the most perfect possible stopping-up. One packs the damp patches, one stuffs of insulator, one stops the air by rolls under the doors… These reflexes must be abandoned in a timber construction, whose insulation is often good besides. The stopping-up led to the containment of wood, and generates rot and mushrooms.

the panels

The majority of the panels are assembled with adhesives which, after Polymérisation, can release from the Formaldéhyde or formaldehyde (CH<_>2O). It is a question of a gas which, in important concentration, can irritate the eyes and the throat, of causing Bronchite S chronicles. At certain extremely sensitive people, serious incommodations were announced. It was discovered recently that the formaldehyde is one of the principal substances attacking the human Genetic inheritance. It is classified like poison and strongly suspected of being carcinogenic. However it enters the composition of the adhesives, industrial varnishes, the disinfectants for large surfaces (grounds of the hospitals…), of heat insulators of the drains, of electrical insulators, of the switches, and some plastic S. the formaldehyde is also emitted by the smoke of Cigarette, the flames of the gas stoves… But the independent sources of emission in the construction industries are the agglomerated panels. At the time of a fire, the released formaldehyde rate is very important.

The issue rate of a panel decrease with time but increases under conditions of moisture and high temperature. It is thus advised not to place it close to a source of heat or to envisage a completion tight with the air.

The classified as panels “E1” have very low a formaldehyde issue rate (less than 9 to 10 Mg by 100g of dry panel). The Contreplaqué S have a weak emission and the majority of OSB as number of MDF are E1. It is preferable to use those which have a technical approval, recognizable with marking on the face or the side, for example ATG/H.701 C E1.

Economic aspects

Prefabrication makes it possible to strongly shorten the duration of the building site, and construction is dry, which makes it possible to carry out the completions more quickly and to live there immediately. This speed makes it possible to strongly reduce the duration of payment of a “double rent”. The lightness of wood makes it possible to do without large machines of building site, which reduces also the harmful effects (noise, dust), and the costs during construction. But prefabrication in workshop, the recourse to general-purpose erecting gangs represent a true upheaval of the trades of the building and suppose the new shape of job management.

During construction, according to the place, wood proves always less expensive than traditional materials, in particular because the speakers are very numerous (logger, docker, conveyer, drier, storage, sawyer, wholesaler, retailer, carpenter), taking each one their benefit, and in certain countries, for lack of specialists.

With equal mechanical qualities and improved thermo isolation, the walls out of wooden are from 15 to 20 cm less thick than of the walls in masonry. The profit of surface is estimated at 10% for a house.

The most important advantage is the possible reduction of the costs of long-term heating, supported by the reduction of the cold bridges and the simplicity of implementation a strong thickness of insulator between the amounts of the framework.

the panels It is also possible to carry out structural members in wood panels. Provided that they are well calculated, the frames produced with panels are relatively economic.

The problem of fire

Wood is certainly combustible but, correctly dimensioned, it offers a resistance to the fire comparable with other construction materials.
The temperature of ignition of wood (i.e. the temperature that it should be reached so that it ignites) is of 250 °C for the majority of the coniferous trees and of 350 °C for the leafy trees. Wood burns only of 0,7 mm per minute (4,2 cm per hour) and carbonized form a protection for the heart of wood lays down it. In this layer, the heat flow is tiny room of more than half. Wood is bad driver of heat and dilates only little. At the conclusion of a fire, under its carbonized surface, intact wood preserves its bearing capacity, contrary to the reinforcements of the reinforced concrete which became deformed, dilated, even generally made break down the structure.

At the time of a fire, wood does not produce toxic smoke, contrary to other materials like PVC joineries which, while burning, release from hydrochloric acid, polyurethane insulators which, them, produce hydrocyanic acid.

Steel loses its carrying capacities starting from 450 °C, as one could see it during the attacks of New York where, after having burned a few minutes, the turns abruptly crumbled. To protect steel from fire one a long time floqué it with asbestos, now prohibited in many countries because of cancers which it causes.

The resistance of the concrete is reduced two thirds to 650 °C.

In the reinforced concrete the reinforcements twist and that rather quickly causes the collapse of the structure. The brick resists in general better than the concrete.

Panels:

At the time of a fire, the released formaldehyde rate is very important.

The problem of the insects and mushrooms

They can make fear, when one sees photographs of small increased animals 10 times, or of Mérule papering a whole cellar, just like reading of the medical dictionary, where the most serious cases are always seen!

The true psychosis which one created around the mérule is worth the sorrow to be analyzed and contradicted. Because if it is true that this mushroom can cause considerable damage, the conditions of its development are very rare, untraceable in a well designed and normally inhabited house. The other mushrooms develop only in circumstances of very strong moisture. Do not either only forget to stop the propagation of the mérule, just as the others Mycose S (in the pieces of furniture or the carpentries wooden of the buildings at least) it has nothing more effective there than sodium aqueous hypochlorite solution such a called Bleach.

The termites terrorize whole France, whereas their damage is limited to areas particular to South-west. Other xylophagous insects are current in our areas but it is advisable to relativize the danger.

See also: List of the xylophagous insects

Mushrooms

A mushroom attack can start only if the wood moisture exceeds 20% (even 22 to 25% for wood more resistant). The normal moisture of a wood is:

• 6 to 8% in a house with central heating (relative humidity of the air ± 45%);

• 10 to 12% in an interior environment (20 °C), with air with 60% of moisture;
• 12 to 18% for a wood external under shelter with a relative humidity of the air ± 75%.

The following faults or circumstances can cause a too high moisture of wood:

• stagnant water;
• condensed water;
• capillary moisture along the walls;
• pipeline water nontight or broken;

moisture of the air a long time too high;

• too high wood moisture during the assembly;
• containment.

It is often a problem of bad design which generates the mushroom problems. There exist means very effective of preserving some (See the practical advices, described further in this page!).

the mushrooms lignivores (destructive)

• cubic Rot
• brown Rot (degradation of the Cellulose)
• Mérule whining
• Coniophore of the cellars
• Fibroporia vaillantii
• Lenzites
• Gloeophyllum

• white Rot (degradation of lignin)

• Trametes versicolor

• soft Rot (degradation of cellulose)

• mushrooms of blueing (weakening)

German: Bläuepilze

Classification: Mushroom of blueing. Distinction between primary education and secondary blueing.
Description and appearance: Blue coloring with black. Often penetrate of several centimetres in wood.

Conditions of development: Temperature: 15 - 40 °C. Wood moisture: > 25%.

Destruction of wood: There is no destruction of wood, but only a coloration.
Origin and causes: Primary education blueing: it is generally the sapwood of sawing and the timber structural coldly sawn which are attacked (pine, sometimes also fir tree, spruce and larch like unquestionable exotic wood such as the koto, for example).

Secondary blueing: wood untreated or varnished exposed to bad weather (doors of garages, doors, coatings of frontages, covered swimming pools, skating rinks, etc). The coniferous trees employed outside must, according to the French standard, being treated against blueing, by products meeting the standard T 72-085

Economic importance: The origin of primary education blueing on coldly sawn sawing and structural timber can involve heavy losses in the sawmills, because the bluish batches are not easily saleable. The damage caused by secondary blueing is rather of esthetic nature that physical. Used in Marquetry to obtain a blue plating (at the XVIIe century) The barks can already be attacked by blueing. The holes dug by the bostryches or the slits of drying are ideal main doors for mushrooms of blueing.

• Mould S (visual) (German: Schimmelpilze)

Classification: Mushroom of surface coloring wood.

Description and appearance: Lives only on the surface of wood, without penetrating in the mass. Often give an appearance of wadding or sleeping bag.

Conditions of development: Temperature: from 24 to 28 °C. Wood moisture: from 30 to 150%.

The growth is supported by humid air and stagnant. Destruction of wood: There is no destruction of wood, only one coloring which can be black, yellow, red or green.

Origin and causes: Attacks wood coldly sawn, but also dried wood, in badly aired and often heated construction industries. This type of mushroom can appear on any surface, of the wallpaper with the plastic (!). The disadvantages of these mushrooms are initially of an esthetic nature, but they can induce respiratory embarrassments and allergic reactions at the sensitive people.

Practical advices

“Protection on plan” or provisions architectural

Introduction

If you discuss protection by architecture, he is professionals who answer you “But of course, it is a question of good sense which to prevent the rain from reaching wood! ” However, the number of timber constructions (frontages, plays, benches) badly conceived and whose only treatment of shock by impregnation CCA ensures for a time the behavior, is impressive.

Others will say to you that a wood untreated will not last, no matter what one can do to protect it naturally, because moisture, the mushroom spores, are everywhere, which the insects steal, and which no architectural provision can prevent some. Contrary, those should visit some 200 year old farms or old churches whose frame, entirely of wood, resisted time without the modern treatments.

While digging a little, one can discover that this art to build by choosing an adapted gasoline, by drawing aside the water of wood, by respecting ventilation, and other things still, is more delicate than it does not appear to with it. And especially that, if it were transmitted by bits in certain trade associations, it is difficult to find in its entirety.

One finds many references of delivers S which treat safeguarding of wood, speaking about the chemicals mainly. But none treats architectural provisions in detail. In each book, there is well a sub-chapter which on a page gives approximate councils as “To make provisions on the level of construction to prevent that are not created in the wood implemented of the conditions allowing the development of parasites”… Which are these provisions? This point is developed little. As if that were not worth the sorrow. Like if this old knowledge, sometimes lost with the wire of time, were not worthy of interest. For example, to pass to fire the foot stakes before hiding.

Framework

There exists a book very well done on the construction of a house-type with wood framework in Canada. A true mine of information from which many the councils hereafter are drawn. But it is only about the system with framework, used especially in America, and little adapted to the climates of certain areas of Europe. The structure of small section organizes bearing walls of wood, often prefabricated in workshop, and which leave little freedom in the later transformations of space.

Construction with framework wood prefabricated are very interesting for the building sites which must go quickly.

Beams

Constructions with beams are interesting for people who decided to be surrounded only of materials 100% natural. They are very extravagant of wood but there is neither suspect insulation, nor problem of vapor barrier… That poses other problems such as the difficulty in passing the pipes in the walls, a less insulation, necessarily small windows… and, for me, the cruel lack of information on the good way of building them. I will speak little here about the system with beams.

Post-beams

It is a way of building which allows a freedom much larger the point of view of installations, because in fact the posts, of broad section are carrying. One can then partition as one wants between this structure, to decide to have a broad open space or to cut down partitions to change organization. All this is of course impossible with the two other systems, where the walls are bearing.

Construction with post-beams is interesting for the young couples. At the time of the building site, the house can be only “closed”, without interior partitions, which costs less than a house to framework. The partitions can be posed well later, when they have a little more money. When the family increases, it will be easy to change the provision of the parts or to increase the maison.
It is easy to build such a house without chemicals: the frame is built with wood of quality, is not confined. If a problem arises, it is visible, one can take measures in time. Wood locked up in the walls anything else carry only themselves and one can decide to take the weak risk to see them attacked. These houses will have a great durability in the change.

The constructive prevention of wood includes/understands all measurements aiming at protecting wood from the moisture and weather action. The purpose of it is to reduce swellings and undesirable contractings of wood, while maintaining its moisture content below the critical points for the attacks by mushrooms and blueing. There exist basic rules and constructive details ensuring the perenniality of wood in the construction industry.

One has habit to say “a good hat and good boots”, but I would like to correct to be more current:

a good hat, platform soles… And especially not of Cagoule!

Indeed, from water can fall from the sky, it is thus necessary to have a good roof or an effective boarding. Water can go up ground, in this case wood gains with being placed far from the ground rather than in an impermeable yoke. And what one forgot at the era of the insulation " thermos" , it is that wood must breathe and that the steam which condenses must be able to be evacuated quickly.

To determine a calendar

A timber construction is in general very fast to realize.
For a house with traditional framework wood average, 12 to 16 weeks are enough to the beginning until the end, without obviously counting the risks such as stock shortage or bad weather. In comparison, a traditional brick building site lasts more than 6 months. It is important to carry out a realistic calendar to hold the machines or subcontractors, but especially to order materials so that they arrive just at the moment when they must be implemented, and so that they should not be stored in moisture.

To reserve a certain flexibility is also important to be able to face the unforeseen ones.

Standard calendar of a house in bone, built in a traditional way:

• Plane, financing and allowed: unforeseeable duration;

• Establishment and casting of the soles: 1 week;
• Foundations, drainage and embankment: 1 week;
• Framework, cover and plaster fillings: 2 weeks; → at this time construction is under shelter
• Portes and windows: 1 week;
• Plumbing, heating and electricity: 2 weeks;
• Thermo isolation, avoid-air, vapor barrier: 2 weeks;
• Coatings external of completion: 2 weeks;
• Linings of completion: 2 weeks;
• Painting, cupboards and apparatuses: 2 weeks.

For a house with framework wood prefabricated:

Once the foundations carried out (2 weeks), the framework, the cover, the insulation, the linings and external, the doors and the windows are brought very assembled on the building site and gone up in one afternoon. Plumbing, the heating, electricity and the completions are finished in two weeks. A house carried out in one month… In condition obviously that the elements are available! In America of the whole cities are built with the chain in this manner.

For a construction post-beams:

After the foundations, one assembles the bearing structure, on which one builds the roof. The walls are assembled only once the completed roof, with the shelter of precipitations. This type of construction more or less takes time according to the constructive techniques, the degree of prefabrication, the number of workmen. But it has the large advantage of putting construction under shelter before even assembling the walls, which is important under the rainy climates.

Protection of wood on building site

On a traditional brick building site, the workmen do not pay attention to moisture, and one protects only seldom the walls in construction. When wood is used, the building site will last less longer, but n the other hand it is advisable to be more attentive with the protection of the sawlog.

Transport

It is necessary to require a transport except rain in a covered truck. As far as possible, the material should be delivered in building site right before its employment, especially in the case of frameworks external of window and door, and materials of external woodwork.

Storage

During normal phases of construction, the timber and the materials of coating are delivered in building site after the foundation is built.
The materials of frame installed before the house is not immured can be wet during a downpour but they dry quickly.
On the contrary the wood arranged out of tight piles can absorb and retain a great quantity of water.

It is necessary to store wood on ground dry and plane, separated by cleats, raised ground and under cover, not to leave the elements locked up in impermeable plastic packagings too a long time (beyond 8 to 12 days for ordinary beams and lamellate-stuck of size).
The materials of interior woodwork will be delivered only once the completed cover, they will be arranged in the house.

Implemented

To wait sufficiently a long time after the implementation of the concrete, masonry, of the rough coat, before placing wood, and especially, well ventilating. Moisture present in all these materials must be evacuated well. A 28 days minimum of latency will have to be respected so that the concrete reached its optimal capacities of mechanical resistance.

To await the complete disappearance of moisture before even storing wood in the buildings.

The foregoing provisions relate to especially the interior finish (floors, skirting) which should not inflate too much not then not to present too important movements. This plays less for the parts of large sections constituting the frame.

Foundations

To seal the foundations at their junction point with the framework by applying to it a layer of sealing or cut of capillarity.

In the case of cut technical a flagstone on ground and independent concrete foundations.

The underfloor space are prone to become very wet and the structural members exposed to these conditions are likely of rot, if a vapor barrier is not used on the surface of the ground. The underfloor space should also be ventilated. When space is heated, the lids of ventilator should be removed during the summer for a better ventilation. The underfloor space should not be built out of wood, but with stone or concrete, like base.

Water arrives on the ground with a certain power and can splash the carrying frontage or elements. The overflow of roof is a first element reducing the phenomenon.

The foundation must rise sufficiently above the level of the ground of the garden (at least 20 cm), ground which will be preferably tilted towards outside to draw aside surface water of the house and satisfactorily to protect the wood completion and the structural members against moisture from the ground.

One will drain as water under the surface of the ground, to prevent as the basement is wet. With this intention a drain or a filter pipe is posed with the perimeter of the house.

Post-beams

The pillars are preferably posed on steel or stone bases having a detail suitable to avoid the increase by capillarity and to support the fast flow of water, or better: the pillars are posed on a stringer low itself posed on the base.

The surface of the ground can be studied to deaden or divert the drops. The gravels are a simple solution and effective, a filament of water or a grid can also be considered. Attention with the naked ground which moreover sends mud on the frontage.

Contact with the ground

• direct contact: unless wood is of a very durable gasoline, this type of contact is to be avoided.
• post posed on a hard base (stone, concrete…) : much better, but the water which infiltrates by capillarity between the two finds wood upright and goes up in the fibers
• the installation of a low stringer under the post opposes to capillary water fibers lying, which absorb it much less, from where a larger longevity
• to separate wood from sitted by pieces of metal: it is necessary to avoid confining wood upright by the installation of a coating for example.

Attention also with the fire resistance of the assembly.

Frame floor

All the wood used for the frame of a construction with framework wood must be quite dry (water content of wood 19% maximum) at the time of its implementation. The stringer of base is posed on the levelling of the foundations, that is to say:

• If levelling is perfectly of level, one poses the stringer directly above or on a synthetic foam trimming with closed cells.

• If levelling is not level, one can sit the stringer on a bed of mortar.

It is necessary to pay attention to the beams fixed in the walls, because the air does not circulate there freely. It is necessary to envisage a frontal and side release of at least 12 mm.

post-beams

The low stringer is posed preferably on a base out of stone or blocks of clay, with a layer of sealing and a levelling. Sometimes one proposes not to anchor the low stringer in the base, for a greater flexibility in the construction.
Actually, anchoring is not necessary. The weight of the framework is quite sufficient to prohibit any movement. The houses of half-timbering were never anchored.

The floor is posed on the low stringer.

Mural framework

The type of mural framework depends obviously on the constructive system, whether they are post-beams, framework or beams. But in the details it will be necessary to adapt each system to the specific climate of the area.

the mural diagram of left watch the way of building most current in Canada. : The insulator is largest possible. There is no blade of air under the boardings. The imprisoned air increases a little the insulation. There is no risk of major humidification, the dry air absorbing all.

Diagram of a system of cross framework and double insulation . The vapor barrier is placed between two insulators. This makes it possible to make pass all the sheaths in the first layer, but raises the question of the strength to the moisture of this insulator. Notice that the vertical boardings are posed on only one bed of cleats, horizontal. The accidentally entered drainage, as well as ventilation, will be done with difficulty.

In Belgium these details would be very bad! In the air constantly wet of our country, ventilation must become the principal concern of the architect.

It is necessary that wood breathes, and thus to leave a blade of air of at least 4 cm behind the boarding to air and prevent that moulds are not formed or that water makes inflate the panels.

The techniques of constructions are as varied as the climates and mentalities.

• Community center of Lentig : The boardings are not jointed, which improves ventilation.
• Room of host in Kobe : a system one cannot simple any more of soldier beams…

Post-beams

The system post-beams, according to me, is adapted more to the climate and the mentality of Belgium. The bearing structure is seen, which is reassuring as for stability. The structure thus better ventilated and is exposed to rotting.

But even in a so small country there are still differences in climate… At the seaside the wind is strong, ventilation will be done easily, but it will be necessary to envisage good joints and a wind shield behind the boarding, to avoid the inopportune drafts. On the other hand in a wet content of valley and with the shelter of the wind, the air vents will have to be oversize, and the wind shield will be useless.

The bearing structure is laid out every 4 meters, with a section of 18 X 18 cm (easy to realize by gathering 3 standard profiles of 6 X 18 cm. One assembles them with through bolts placed every 80 cm or with notched plates.) With the right of the stages the assemblies are done by bracing the beams and the posts.

The constructive principle current is to place the wall in itself outside the structure, to avoid the insulator ruptures.

The walls consist of pieces of wood of small sections, because nonbearing, placed preferably every 60 cm, because the panels make 120 of them, and enclosing the insulation. If the structure is such as it forms rectangles broader than high, which is the case more running since the stages have a height from 2,5 to 3 meters and that the distance between centres of the structure is of 4 meters, the framework of the walls will be posed vertically (as on the diagrams following page). In the contrary case, a double stage for example, the mural framework will be posed horizontally, and this with the aim of limit the ranges.

One in general advises to place a vapor barrier on the interior side of insulator. The main issue of this technique is that the holes, inevitable, from this impermeable layer (by the nails, accidental tears, joined to the right of frames etc) will concentrate the vapor and it is at these critical places that initially will pose the problems of moisture.

I prefer to place a panel of OSB, 18 or 22 mm, classifies III Sterling (very dense, containing paraffin) which will play the part of slow down-steamer. The joints between the panels owe, them, being tight! Moisture crosses only very slowly this layer, and provided that the materials of the wall are gradually increasingly permeable with the vapor (not question of insulating with expanded polystyrene!), moisture will be gradually transported outside without causing damage. It is possible that a little water condenses a little everywhere, when the weather is very cold, because the dewpoint can be reached. It will be always better than a problem of perforated vapor barrier where all the condensate at the same place and where moisture can truly become problematic.

However there exists a surer system, which is to pose between insulator and the blade of air a panel of under-roof “softwood”, (Celit 4D or Gutex, still more bio) insulator and breathing, permeable with steam but resistant to humidification accidental, which prevents that the dewpoint of the air is reached in insulator even, by thermically separating this one from the blade of air.

Half-timbering

Between the posts and beams of the structure, one traditionally puts a mixture of clay and straw. The straw is insulating, the ground accumulates heat. When it rains on such a frontage, the clay of surface, humidified, inflates and pushes against wood, so that there is no joint where water can infiltrate. The clay mass is not humidified. Clay has this astonishing characteristic to be hygroscopic (to absorb then to reject water according to the hygroscopy of the air) and to be tight at the same time in its mass. This phenomenon is noticed in the gardens with argillaceous ground, where the watering or rainwater does not penetrate in the ground, and forms small puddle pools. Clay, therefore, pump the water which is with its proximity, i.e. close to wood. What protects wood well, always drained by the clay which is against him. The Ground-Straw is an acoustic good isolating thanks to the flexibility and the mass from the raw ground… While being very cheap.

But it is difficult to respect the current standards of insulation of the walls (k55) with this system! In more the joint between the posts and the wall opens with the withdrawal and the cold air passes directly in the house if a particular detail were not envisaged. It is possible to build in cob with the proviso of thinking the details well, but it is necessary to call upon a specialist. Begin work in spring because it takes 2 months hot and dry so that cob dries. If you start in autumn you be likely to live all the winter with a very unpleasant wet wall.

Cob is packed and an enormous joint is formed above the wall in 1 month ½ approximately, joint which it will be necessary to fill with bricks with cob sèches.
Such a coating is demanding, and it should be renovated from time to time, which is not always accepted by the inhabitants. One then saw some furnishing space between wood with brick and cement. This does not pose any problem in an interior wall, but outside, if the frontage is not sheltered and that the brick undergoes the rain, of the troubles can occur: The brick suffers little from rainwater. But its alveolate structure is porous like a sponge. It is thus gorged with rainwater (even in dry weather there is moisture in bricks). Not only the brick does not pump the moisture contained in wood, but it brings water until him. Wood is then wet permanently, and ends up rotting at the confined places…

The worst is still the covering of the frontages with half-timberings by cement: it occurs cracks with the right of wood, where water returns. It remains captive inside, making mildew all the section, well with the shelter of the glances. If the coating is withdrawn and that one lets breathe the structure, it is possible to save it.

The stages can be shifted the ones compared to the others so that the beating rain does not reach them. To envisage profiles, references of water, gutters evacuating rainwater quickly. One can also build eaves in accentuated overhang.

Wood in large sections pumps moisture by its fibers. If the base or the top of a piece of wood is in contact with moisture, it will rot very quickly. On the other hand, wood resists moisture very well perpendicular to fibers. All the details of assembly must thus place at the “dangerous” places a part of strong section presenting its fibers perpendicular to moisture.

Example on a traditional house in half-timberings : The vertical posts are protected from the contact of their fibers of end with water: high: by a horizontal beam carrying the roof low: by the low stringer on which they are posed.

External boardings

secondary Framework

The implementation of the boardings first of all implies a secondary framework, an intermediate work between the carrying structure and the boarding. This secondary framework is in theory obligatory (there is not in system 1, to see post-beams)

The secondary framework is made up either by Tasseau X, or by rafters (in the case of the insulation by outside), or by two cross beds of rafters and Tasseau X, or by metal sections. The installation of the Tasseau X must allow a circulation of air the back of the boardings and L `water run-off accidentally introduced between the boarding and the avoid-rain.

System 1

The blades are posed on walls with framework wood not comprising an external facing, the wind-bracing being interior. The horizontal boarding is supported directly on the structure of the walls, by leaving a blade of air of minimum 3 cm between the boarding and insulator. It easy, less expensive, but more is risked, because so of water infiltrates, it reaches the insulation directly, and if this insulation subsides, it is pressed directly on the boarding, from where an increased risk of rotting.

System 2

One added a plate of celit 4D or Gutex outside insulator, to protect it. In this case it will be necessary to envisage a bed of vertical cleats in the case of a horizontal boarding, and two beds crossed in the case of a vertical boarding. Attention not to pose only one bed of horizontal cleats for the vertical boarding because accidentally entered water could not run out, and ventilation would not be assured.

Half-timberings

In the case of a traditional cover of half-timbered house, the blades, verticals, were posed directly on the beams secondary, horizontal, of the structure. There was no blade of air and the shingles ended up rotting. The inhabitants replaced them every thirty years.

standard of blades

1. blades for installation with covering joint or covering

2. blades for installation by joggle, C. with. D with a worked profile

A. with leaning and open joint

B. with grooves and strips

3. shingles

The first two systems being usable horizontally, vertically or tilted. If they are with grooves and strips, they can be used only on the condition of taking account of the direction of the wind and to be sheltered. Horizontally, one will preferably use boards with profile studied for the water rejection. The installation of the shingles is detailed in a card in appendix.

Blades posed horizontally: case of figure.

....... ................... B .................... C HAS .................... D .................... E .................... F .................... G

Bad a:: A joint on two receives the rain and will rot

Bad b:: Water running on the boarding is likely to penetrate by capillarity

C: good: Water runs on the boarding with little possibility of penetrating there

D: Very well: The profile of the blades is especially studied to reject water.

Pose with covering joint:

E: means: the water which runs on the lower face can go up by capillarity.

F: better: The profile is especially studied to reject water.

Joggle:

G: well: water always runs to the bottom, the boarding is well ventilated, but a gust of wind can make land a drop on the avoid-rain, which will have to be quite tight. (1, 31 & 74)

In theory, the installation of the blades in a vertical way is advised because it allows a faster flow of rainwater. This installation however requires a total protection of the ends of the blades by an overflow of roof. Unfortunately certain urban regulations limit these overflows to an insufficient minimum to protect the boarding. A horizontal installation is then preferable. (22)

The thickness of the blades will be selected according to the nature of the support (continuous or discontinuous), of the impact resistance and to fire. The most current thicknesses are 18 and 22 Misters. One uses in a current way of the blades thickness higher or equal to 15 mm for a distance between centres of the supports of less than 40 cm, and thickness higher or equal to 18 mm for a distance between centres up to 65 cm.

The exposed width of the blades will not exceed 7.5 times their thickness, except the Western Red Cedar, up to 10 times. It should be known that the tendency to the warping of a part will be all the more large as its twinge (width-thickness ratio) will be high. The marketed dimensions most current are:

24 X 60 mm with 24 X 80 mm for the chestnut

18 X 125 to 22 X 145 mm for the fir tree, the spruce, the woodland pine, the maritime pine and the Douglas one

18 X 140 to 19 X 190 mm for the western red cedar

The length of the blades is limited only by the availability the big lengths.

The covering of a blade on the other is at least 10% of the total width of the blades, and 20 mm for the blades of 190 mm width. It is also necessary to spare a play in the assembly to allow the movement.

the end of the blades

horizontal blades: if it there does not have a groove and tongues in end, connection must be done on an amount. It, like, is everywhere advised to spare a play of 1 Misters.

Vertical blades: the blades are fixed on at least two supports. They are matched in end, the partly higher strip being placed or one builds a plaster filling or one envisages a profile with water rejection.

the shingles

The average thickness is measured in the middle of the length and must be of at least 5 Misters. The width lies between 6 and 30 cm. The length lies between 20 and 60 cm.

At the time of the placement of wood it is necessary to take care of an optimal orientation wood blades compared to the rain, to support a good ventilation and an effective flow.

Safeguarding

For wood durable (for example, the Western Red Cedar, the wood more used in boardings thanks to its joint qualities of durability, low density and facility of machining), the question of the completion is of nature strictly esthetic. Without completion, wood will take a color grisâtre. Wood become gray does not require any maintenance. On the other hand one can decide to apply a top coat, that it is by esthetic concern, to avoid the movements due to moisture or because the air is polluted. Indeed, the soot particles present in the atmosphere cling on the relatively rough surface of the wood, which becomes gray dark then with noirâtre, instead of taking a beautiful silver plated color. Caution: Once the completion applied, it will have to be maintained. Better is worth not to put completion if is to let it worsen.

Ends

The treatment of the ends of the boarding is very important. Partly high, the overflow of roof protects wood from the rain but also from the ultra-violets. Partly low, the boarding should not go to the ground, because of the splashes and the capillary increase. The ground clearance must be 20 cm minimum. These two ends must be equipped with vacuums guaranteeing the air intake in the space of ventilation, and grids preventing the rodents or the birds to penetrate there. (6)

the angles

The angles are a weak point in the boarding, because of the presence of end grained timber, which it will generally be necessary to cover with a filler. They can also become an occasion of architectural expression, by the way in which the assembly is carried out.

Horizontal stacking and even the vertical juxtaposition produce joints where water can infiltrate. In addition to a ventilation behind the boardings, it is highly recommended to envisage a broad overflow of roof to protect wood durably.

In the high buildings one recuts the blade of air, to avoid the effect of chimney in the event of fire but also to obtain a joint marked well between the vertical blades. I prefer the detail of right-hand side because precisely in the event of fire, metal tends to melt very quickly… (6)

Plaster fillings

A plaster filling should be used with all the junctions. The intersection of two types of materials is a typical example of construction which requires a plaster filling. The coating is separated from a wood facing below this one by a moulding-drip. To prevent water from being introduced into the wall, a formed plaster filling is posed above it drip so as to draw aside the water of the external edge. The plaster filling must be prolonged of 8cm above this moulding under the sheathing paper. This kind of plaster filling is also used above the windows and the doors unless they are protected by other thing, and other projections where it is possible that water is introduced into the frame. (5)

For the implementation of the panels derived from wood in external coating:

- on the level them joined horizontal, to have the metal flaps or to ensure the covering of the lower plate by the higher plate

- on the level them joined vertical, to set up a metal section or a splice plate out of sawn timber or panel.

fixings

To only use, even if they must be covered, of the fasteners and coated with zinc or made fixings of a stainless metal.

To envisage the dimensional variations due to the changes of moisture, and to hold of it account for the design and the implementation, by leaving a play in the joints and by not fixing the parts in a too rigid way. For example the wood blades will be fixed only once on each cleat.

the connections

To avoid or cover the corners, joints, the grooves in which water could stagnate.

In all the cases to avoid the traps with water to avoid the increase by capillarity. To also avoid end grained horizontal timber surfaces exposed to water. To practice oblique cuts or to cover these surfaces.

To avoid the metal parts crossing, for example with the connections of interior buildings on outside, because they constitute a cold bridge which generates condensation. If necessary, to seal the ends of the ankles and the pins with stoppers out of wooden external side.

the frames

They must further present a profile driving out water possible towards outside, especially in the low part, who is most exposed. A large “nose” cut in the same piece of wood that the remainder of the cross-piece is preferable with a small added profile.

Choice of wood

1. One will choose an enough rigid wood to support the efforts to which joinery is subjected (force of the wind, but also handling). Accordingly, the density is important, owing to the fact that there exists a relationship between this value and the rigidity of a wood species. It is especially for the exterior wood finishings with more important dimensions (2m50 and more) that it is important. For timber broad leaved, a density of 500kg/m ³ is with being advised, for the coniferous trees, 450kg/m ³. If the density of a wood is less, the sections envisaged will have to be increased.

2. the dimensional stability of wood is important to avoid the losses of sealing, the opening parts which wedge, etc One will choose a species of which dimensional stability is good or, failing this, another species, but dried carefully. For information, one says that the movement between 60% and 90% of moisture is

• weak: movement lower than 1.5%: good dimensional stability
• average: movement between 1.5% and 2.8%: average dimensional stability
• high: movement higher than 2.8%: low dimensional stability

(in appendix, a table of the movements of unquestionable wood and a wood list being appropriate for the frames)

3. Of the pieces of wood containing of the wood of tension or compression cannot be used in exterior wood finishing (a tree subjected to constraints risking to unbalance it or tear off it, a steep slope or winds dominant for example, produced wood of tension (leafy trees) or wood of compression (resinous), from which withdrawal-swelling is completely different from that of normal wood.)

the details

It is mainly with the right of the windows that the installation of a vapor barrier is problematic. The theoretical cuts practically never are well applied. It results from it from the defects of sealing at these places however most significant.

The lacquers do not penetrate in wood, they form an impermeable layer with water and the air. For this reason it is necessary to take some precautions before applying them:

• wood must be dry during the application.

• All the faces of wood must be treated with the same product of completion. Indeed, if the outside of wood is enamelled and the lasuré interior, the steam coming from the interior of the house passes the barrier of lasure, crosses wood, and is found blocked other side, between wood and the lacquer. Moulds can then occur under the layer of lacquer. For this reason I disadvise formally with those which bought frames untreated to paint them of a film forming layer, because they are extremely likely to see painting forming blisters, fissuring, and their wood to rot whereas it was not at the beginning not to be treated… Our old always painted a coat of paint or additional varnish inside the building.

• the frontages exposed to the South can heat very extremely in summer, which causes also the cracking of the lacquer.

• treated interior parts must-being covered with a signal, varnished or painting to avoid the risk of harmful vapor emanations.

thresholds of window.

It is advisable to worry about their form to make sure that the rainwater is well rejected towards outside. For that it matters that each threshold is overflowing of at least 4 cm of the finished level of the frontage, that it is provided with a break-in drips (also called water drop), and that of each with dimensions he goes up a little to prevent that water does not run on the frontage by leaving traces of moisture under the windows.

Various styles of breakage-drop are possible, of half-round the (A) to old, with the triangle (C) more modern, while passing by the square. The quarter of round (B) is correct only in the drawn direction, while special profiles are possible provided that water does not on the occasion to pass. For that one needs a height of 6mm minimum and an increase not too near to the horizontal one. Borderline case: (D).

Interior

confined moisture

It is not moisture as such but the containment which generates the problems. There is no risk in a room to sleep, but the bathroom, the kitchen and the wash-house produce much moisture. This one condenses and if ventilation is not assured, wood starts to mildew in the dark corners.

Condensation appears when the temperature of the walls is lower than the dewpoint. In constructions with framework wood, this phenomenon only occurs very seldom on the surface, but it appears sometimes inside the walls, involving pathological disorders. The degradations caused by this type of condensation can be very important because their demonstrations remain a long time invisible. To avoid it, one in general advises to place a vapor barrier in front of insulator, interior side, and to especially ensure his continuity, which is very delicate, in the details.

The risk to concentrate all the steam pressure at the critical places, because it is always there that the vapor barrier tears, is too important. A continuous panel of OSB classifies III Sterling paraffined replaces the vapor barrier advantageously, on the condition of using a breathing insulation, and to comply with the basic rule: The components of the wall must be increasingly permeable interior towards outside.

It is also necessary to break down the invisible or confined zones, without forgetting to air the part in question carefully (to open the window after the bath!)

The coatings must be posed by envisaging a light play making it possible the blades to undergo without damage the withdrawals and swellings due to the changes of the hygrometrical state of the ambient air. The wood moisture should equalize, at the time of the installation, that which they will have in service (10% for the floor, 16% for the frame). (3 & 73)

Coatings of walls and ceilings.

Like the external boarding, the ornamental panels inside must let the air circulate behind them. Ventilation is ensured by the installation of a double bed of cleats or by their discontinuous installation. The bottom and the top of the work must leave a passage to ensure a continuous flow of air. It moreover is advised to move away wood from the ground of approximately 10 cm.

The use of products of completion is recommended if the coatings are likely to be in contact with greases, water or vapor, as in the kitchens or the bathrooms. The varnish must be applied preferably before the installation of the panels. In all the cases, the two faces must be treated with an equivalent system of completions. (3)

Contact between wood and masonry

Attention with the parts of wood which are locked up in masonry (typical case of a beam in the load-bearing wall). There is risk of rot when the beams are posed with joint tightened in the mural chases so much so that moisture cannot easily escape. The chase in the wall for these beams should be sufficiently large to leave a space of at least 1.5cm on the sides and the end of the beam for ventilation. (5)

Floor coverings

The floor is posed on the low stringer. (71)

For the choice of the wood of the floor, dimensional stability and hardness according to the use are more important than durability.

If one decides to integrate an underfloor heating into the parquet floor, it is necessary that wood is sufficiently dry at the time of the installation (8 to 10% for the mosaic parquet floor or with blades, 7 to 9% for the pasted parquet floor) and that the cover has a suitable water content. One advises to make turn the heating to the test before posing the parquet floor, by increasing the temperature of the water of max. 5°C per day until max. 35°C to pose the parquet floor, the ground must have a temperature of 15 with 18°C during a few days. The temperature of the water of the underfloor heating should never exceed 55°C. The water pipelines should be spaced of 150mm (300mm maximum). At all events wood will present a withdrawal. Fine shrinkage cracks will appear during the use of the heating and the joints will open somewhat, which is not a problem in oneself. (22)

(in appendix a wood list being appropriate for the floor coverings)

Ground of the bathroom

Sawn timber can be used as floor covering in a bathroom, but it is not advised. The moisture of the air is only one small portion of the problem. It frequently happens that the water of the splashes can penetrate in the joints, and create a permanent moisture under the elements of the parquet floor. To avoid that it is necessary to run a thick layer of epoxy adhesive under the blades, to apply a varnish in completion and to renew the layer of varnish regularly. It is necessary moreover to leave an expansion joint to the circumference of the part, by preventing water from penetrating there with a silicone joint. All this is very complicated, no error tolerates and leaves with wood the only role of decoration. (22)

According to me it is possible to use wood in floor covering for the bathroom, but while agreeing to leave open joints and a space of ventilation under the floor, like one does it for the external terraces. It will of course be necessary to envisage a drainage, and to use a durable wood.

Staircase

For a staircase, one needs a wood which has: A resistance raised to wear, a good rigidity and a good solidity, weak a Fissility, weak a Rétractabilité, a good machinability. List nonrestrictive of wood being appropriate for a staircase: Oak of Europe, Maple of America, Ash, Guatambu, Beech, Pine, Douglas (Oregon Fucks), Southern Yellow Pine, Afrormosia, Afzélia, Iroko, Merbeau, Moabi, Red Balau, Panga-panga, Sucupira, Tatajuba, Wengé,… (22)

External elements

projecting elements

One envisages coatings in Cuivre, in Zinc, sheet, or other, on the higher face of the structural components out of wood exposed to the bad weather (pergolas, beams and frames prolonged towards outside).

The elements exposed to the rain will not present end grained timber to the top, will be cut skew rather than horizontally, profiles studied for the rejection of water will have.

Above: On the left, a post cut right will quickly be deteriorated by the water which will remain stagnant there: bad!. An oblique cut is with being advised, but it is moreover necessary to envisage one product of protection because wood presents its fibers of end to the rain. The angles strongly rounded (3 has 5 mm) prevent the wounds and mechanical deteriorations of wood. On the right, a board protects the post while presenting fibers lying to the water, which will be able there with difficulty to only penetrate. It is the best solution. the terrace

The terrace is the application which requires wood most durable (classeI-II), since it is exposed to the bad weather without protection and that it remains often wet for very long periods. But durability is not sufficient. It is necessary also that wood is solid and that it has a sufficient resistance to wear. A light species as the Western Red Cedar is indicated little for a terrace where the traffic is intense. Not only the distances between supports should be considerably reduced, but the terrace would be exhausted too quickly. It is reasonable to consider that starting from 600kg/m ³, these problems do not arise any more. Dimensional stability is certainly important, but less than for a frame. One thus uses in terrace wood durable which is not enough stable to be used in joinery, and which is thus less expensive.

List nonrestrictive of wood being appropriate for a terrace: Afrormosia, Afzélia, Azobé, Bangkirai, Bilinga, Ipé, Iroko, Jarrah, Chestnut, Massaranduba, Merbeau, Moabi, Padouk, Robinier, Tatajuba, Teak of Moulmein (not Teak of plantation!)…

Grisaillement or the blackening of wood can be avoided only by applying a pigmented top coat. It is however difficult to keep in good state the top coat of a terrace, because of the traffic, of the stains, the displacement of pieces of furniture of garden… In almost all the cases, it is advised not to apply of top coat and to leave wood grisailler. (22)

The rafters on which the boards of the terrace are fixed are them-even placed on small blocks (thickness 20mm), out of matter imputrescible and noncapillary, which allows the drainage and isolates wood from permanent moisture. Headroom under minimum floor: 5cm. In the event of persistent rain one can expect a swelling of 5%, therefore a board of 10cm of width can widen 5mm. For this reason the joints left between the boards have a width of at least 10mm. (26 & 55)

the external staircase

For the requirements for durability, it is necessary to add requirements of mechanical resistance, frost resistance and dimensional stability. It is moreover desirable to return not the steps slipping.

List nonrestrictive of wood being appropriate for an external staircase: Afrormosia, Chestnut, Tatajuba, Wengé, Most stable: Afzélia, Ipé, Iroko, Mahogany tree of America, Merbeau, Padouk. (22)

The roof

the frame

Moisture also goes up in roof. The frames remain often apparent, especially in the old buildings, and that has a protective effect for wood. Constant ventilation avoids the formation of moulds. It is advisable to be attentive, in a restoration for example, not to lock up wood in the insulation.

• If the roofs are used as attic, it is more intelligent to isolate the ground from it, that will avoid moreover heating this nonlivable volume, and will reduce the consumption of energy.

• If one transforms the roofs into livable part, to take care to place the insulation so that it does not lock up wood. This can be carried out in particular by shifting the insulator carpet towards the interior, so as to let circulate the air behind him. It will be necessary moreover to envisage an air intake in bottom and an exit of air in top.

A vapor barrier (or a slow down-steamer) is necessary on the hot side of the walls and the ceilings. But even when a vapor barrier is used, a certain quantity of moisture arises around the pipes and other openings, and sometimes even through the vapor barrier itself. If moisture accumulates with the entretoit or under a flat roof, the vapor can condense at certain places and cause damage. The best method to remove this moisture under the roofs is to ventilate sufficiently.

It is current to practice openings under the overflow of a roof on pinion or in croup. The movement of the air by these openings depends mainly on the direction and the speed of the wind. Additional openings close to the ridge improve the system.

A continuous vent or a latticed slit is appropriate to ventilate a flat roof when the insulator is placed between the beams of roof on the level of the ceiling. Each space between the beams will be broken down. When the insulator is installed on the coating of roof, the surface between the beams should not be ventilated.

It is also necessary to give an special attention to the end grained timber, the ends of farm, the cavities and the perforations, because these parts more quickly absorb moisture by capillarity in the vessels of wood. Y to apply a cut of skew or to cover them with a filler. When condensation is inevitable, to envisage the drainage of water. To think of breaking down the vacuums under floors and roofs.

The diagram below represents a test of cut in a junction wall-roof, for one of the two systems. These examples selected like were adapted to the Belgian climate:

Post-beams breathing

Air ventilating the boardings and the roof Is represented by the gray arrows.

Framework

the Cover There exists of old roofs out of wooden, and they resist the bad weather rather well. However they are most exposed! But if the roof is quite sloping, and that the shingles are split (not sawn!), rather coarsely not to stick the ones to the others, and thus not to produce capillarity and to leave a certain ventilation, the whole dries rather quickly after a downpour not to leave time to mushrooms to develop. With the mount Saint Michel one notices many roofs in shingles of chestnut. A slope of 30° minimum and a good ventilation between the shingles and the structure are the best guarantors of the perenniality of a roof out of wooden. At the end of this text you will find soon a data sheet explaining in details the installation of the shingles. (source: Van Hoorebeke Panels, Belgium)

In the countries where it snows much, it is necessary to take account of the snow melt of the roof. Above the house, heated, snow melts. But on the overflow of roof it freezes and it is formed a dam of ice which retains water on the level of the beginning of the overhang. A good insulation of roof reduces the phenomenon, but one advises in addition to placing a protection of overflow of roof, which must be prolonged upwards, at least 30cm beyond the interior face of posts forming the wall. I placed this protection on the cuts of the two preceding pages but it seems that it is not really essential in Belgium, taking into account the little of prolonged freezing which we know.

When the roof is composed of wood containing of the corrosive matters (ex: Western Red Cedar), the gutters, chêneaux, valleys, etc will have to be realized out of stainless steel, or copper in certain cases, with 0,8mm thickness minimum.

Moreover

“Natural Protection” or wood more resistant

Choice of the gasolines

Wood can be classified according to their durability.

After having conceived construction in his details and bench the classes of risk, one can choose the gasoline adapted to each use. The wood subjected to an intense humidification (pieces of furniture of garden) will be preferably selected of class of durability I (very durable), the wood subjected to an occasional humidification (not protected vertical walls) of class II, etc

One finds wood naturally resistant in Europe or elsewhere. When one speaks about ecology it is necessary to think of the economy products which one carries out by preferring a durable wood, but also with the problem of pollution per transport which wood coming from remote countries poses. There exists wood durable in the majority of the countries and it is thus not necessary to seek very far.

It is important to make sure that the wood which one buys comes from well managed forests, history to ensure the survival of the men and the forests everywhere in the world. The first world label attesting the good management of the forests is the FSC. It was developed after the conference of Rio 92, for the social aspects and environmental of the trade of wood. It is possible that soon a label Iso 14.000 equivalent sets up.

There exists a European label, PEFC, which starts to extend in Canada and other countries, but does not treat wood tropical.

The labels place Belgium in the poor pupils. Why thus? Half of the Belgian forest inheritance is divided into small family properties. However, the asking price for a certification of good management by the FSC is fixed, whatever the importance of the property. Much too expensive for the small producers! Moreover, for each passage of generation it is necessary to pay death taxes, rather heavy. Not to have to sell part of the grounds, or to borrow, the heirs proceed then to a massive cut, too young trees. They plant also trees with rapid growth, to be likely to benefit them-even from their plantation. Indeed, if a man plants oaks, it is its great-grandson who will benefit from it. You said short term…

One generally leaves the principle which wood dark are more durable than those of clear color. But it is an error, certain wood lights are quite as durable. It also happens that the same species presents important differences in color (Dark red Meranti: the color varies red-brown dark with the brown one clearly the rosatre.) It is usable classifies 3 of them if its density is higher than 670 kg/m ³, which has nothing to do with its color…

This chapter presents especially wood Europeans, with some precise details of color or characteristics:

the Oak It is the leafy species most used in the North of Europe. Its drawing and its color characteristics are known for the pieces of furniture, the beams of the ceiling, the staircases of the hurdy-gurdies residences. The oak pushes in Europe and in other areas. On the other hand, the denominations “oak of Brazil” or “Asian Oak” are used for wood not belonging to the Quercus kind and are thus abusive. The current denomination of Oak is reserved for the kinds Quercus Robur, pedunculata, and petraea, which has a good durability (II-III). The white oak of America (quercus alba) resembles the oak of Europe extremely, but pushes more quickly. Attention, the red oak of America (quercus will rubra or borealis) has a less raised durability (IV). The oaks tend to fissure during nailing, and contain tannins which can, in the presence of moisture, to give a coloring blue-black to the places in contact with ferrous materials. (28) jhb: lbn

the Robinier False-Acacia It is the most durable wood which pushes under our climate. It can be used in class I or II without treatment. It resists even the termites. Except ground and exposed to the bad weather, it can resist 60 years! Unfortunately its reduced dimensions limit its use. It is difficult to get some in big lengths. Robinier is also a very nervous wood (what is the cause of reduced dimensions of the parts) and is split quickly if it is subjected to constraints. But in small sections, it is a good alternative to wood tropical.

the Larch The Larix kind includes/understands ten species, all originating in the Northern hemisphere. The Larches are fairly durable (III), and have a very distinct sapwood. The density of the larches of mountain can reach 750 kg/m ². Their rigidity and their strong density make an excellent wood of structure of it.

the Douglas

Resemble fir tree, but has more raised durability. As in more it pushes quickly, it became a timber very much used in France.

Period of cut

It is important to recall that the quality of a wood, in addition to the species, also depends on the climate, the ground, slope conditions in which it pushed, at which time one cut it, the way in which one dried it and output.

Popular wisdom dictates periods to cut wood, generally related to the Catholiques festivals, which were the temporal reference marks easiest in a company where the common peoples did not have a calendar. The Oak in Christmas, the Birch enters two Notre-Dame. Because for these periods the sap is descended in the roots. Wood is thus naturally purged what makes it nutritive for the insects…

A manner simple to envisage the dates of cut of the trees according to the future conservation consists in being based on the moon. However, a distinction must be made:

when the sap is likely to support mushrooms and insects, it is necessary to cut the trees except sap, i.e. out of the downward moon and season of vegetative rest of the species, i.e. in general the winter in Atlantic climate, in February - March or sometimes in August - September in Mediterranean zone, etc This case relates to all the leafy trees in general. Attention not to confuse " the moon descendante" who relates to the fall of the moon compared to the horizon (position " with-dessous" orbit of the soleil") and " the moon décroissante" who relates to the moon phase going from full moon to the new moon!

when the sap protects wood (case of the coniferous trees), it is necessary on the contrary to cut wood in sap, i.e. out of the rising moon and season of growth. There too: not to confuse " the moon montante" (position " with-dessus" orbit of the soleil") and " the moon croissante" who relates to the moon phase going from the new moon to full moon!

Wood tropical do not know seasons. Can one cut them any time? One practices there sometimes the annellation, i.e. one removes a ring of bark to the foot of the tree, to prevent the sap from going up. The tree loses its sheets then. After this artificial winter, one cuts the tree, which already dried on foot.

The annellation was practiced also on our premises in wintry time, and one let the tree thus dry on foot during one or two years. This practice is prohibited today due to extension risk of the diseases… In Scandinavia one practices also the étêtage.

The coniferous trees, the Beech, the whitewood and with duramen nondistinct must be shot down before the end of April. If required to exploit wood rich person out of starch (Ash, Charm) in May.

Why these theories cause do if little passion among the professionals of the sector? It is certainly about a social and economic problem. If everyone required wood cut of the good season, the loggers could work only a few months per annum. What would they make the remainder of the year? Layoff in prospect… The traditional solution was seasonal work. The “men of wood” were loggers the winter, and carpenters at the beautiful season. This system had an additional advantage: The building sites were undertaken only in spring-be, period when constructions dried more quickly and were less likely to be attacked by mushrooms before even being completed. But in the current socio-economic context, seasonal work is too badly considered so that the professionals accept the challenge!

Still some historical characteristics:

The Pin gemmated is a maritime pine which one collected the resin during long years. When the tree is too old one cuts it and one employs it, like the other pines, in construction. It was noticed that the gemmated pines have a durability larger than the current maritime pines.

One tells that the wood used for important constructions, like the cathedrals, was cut by the downward moon, a few days before the new moon, by calm wind of South, South-west…

Everyone agrees to say that the Beech is not-durable. However, Jean-Marie Satgé, sawyer of shingles of robinier in the area of Biarritz-Doors, located one day a roof (!) in shingles of Beech untreated, old 50 years! According to the criteria of commonly allowed durability, it is perfectly impossible. But if these shingles had been cut at the good moment of the year, the good lunation, and all…??

In Europe, one considers that the roughness of the climate of the Alps confers on the trees a higher resistance and a durability. It is also said that the oaks intended for naval constructions were to come from very wet grounds… The Northern wood of the slopes are more durable than those of the southern slopes, because they develop less quickly and them rings are tighter.

Drying

To output the barks immediately, to bark the coniferous trees The slow dessication under bark is reserved for wood hard and very hard.

Conservation after drying:

1. if wood were dried naturally: to preserve under dry hangar, to avoid the contact with the ground and the contact of the barks between them by means of holds, to lime the ends (more fragile)

2. if wood were dried artificially: to store in a room suitable to preserve its state of desiccation

to him

One can store wood some time in the room where it will be implemented so that its moisture is in balance with that of the room.

That it is what one in general says.

According to Yves Hayot, best is to saw wood right before Christmas, to profit from cold and not very windy time for drying. And if one then cuts wood to Christmas? There is one year old “to float” wood, i.e. to leave it in water. This practice makes it possible the sap to leave wood. Unfortunately it is necessary to find place to do that, a river preferably, because the construction of a tank is really very expensive… For lack of river, Yves Hayot is satisfied to saw wood at the time of the order because for the timber, there does not require for drying if wood were cut at the good moment.

“To build the stalls of the cathedrals, wood was cut at the beginning of the building site. One stored it in salt water, then one discharged it into fresh water. The building site being very slow, wood spent one very long period in water. Once sawn and worked, it does not present only one slit! ”

One can with difficulty dry a wood in lower part of 18% with the free air. For certain applications, one advises artificial drying.

“Artificial Protection” or products

It is necessary to preserve wood when its natural durability is insufficient to guarantee the longevity of a work, and only in this case. The preservatives of wood contain biocides of which one should not use, for obvious health reasons, which with measurement.

If the architect made well his physical work of prevention and of suitable choice of wood, the products should not be necessary. Moreover, the errors made on the level of the constructive prevention of wood can be repaired, neither by chemical preservatives, nor by other surface treatments which would not make, at best, that to delay the appearance of the damage.

But it is true that one will often treat the bearing structure of the house, even if wood used is durable, because one never knows, rare are wood which can truly resist all the existing insects… And the small proportion of treated wood is that which supports the roof above our head!

Certain products like oils and the bitumen are used since always protecting wood. Other natural products made their appearance more recently, and use in their composition much substances known for a long time. Many natural products or biological exist, but the stores propose of it generally only one mark or two, and this only for reasons of problems of storage.

Heat treatment

It is a new process, developed for example by the École des Mines, in Wageningen in the Netherlands like in Canada, which remains for the experimental moment; it is too still much early to know the true advantages and disadvantages.

The heating should improve the durability and the dimensional stability of wood, without biocide contribution. By a thermolysis (heating with 150-200°C in aqueous medium), a conventional drying then a second passage in a furnace, dryness this time, this technique splits up hemicellulose by binding it to lignin, itself also partially modified. This causes the appearance of a reticular structure and makes these components of wood less recognizable, therefore less accessible, with mushrooms.

Hemicellulose cannot either any more attract water present in the ambient conditions, and the hygroscopic balance (EMC) of wood will not exceed any more the 17%. One is thus in the presence of a matter which is not truly any more of the wood, which will not play any more a regulating part of moisture, but, put aside the energy expense for the furnaces, this method seems rather ecological at first sight, especially for high-risk uses as outside.

oils

Oil in general is the surface treatment simplest, cheaper and most ecological. It protects wood from water by playing the part of filler. It impregnates wood, is nonfilm forming, and lets pass the steam, which makes it possible wood to dry if it were accidentally humidified, but with a less resistance, in particular in the presence of mechanical requests. The final improvements are easy to realize.

The linseed oil is a natural protection used for a long time to protect all wood, interiors like outsides under shelter.

Hard oil protects wood from floor coverings all while letting it breathe, and has a certain resistance to the mechanical requests

salts

The Sel of boron is a white powder which one dilutes in water to whitewash wood of it. It is known for a long time like interior protection against mushrooms, and repulsive against the insects. Outside it is very quickly washed by the rain and is thus not used.

Other salts are known and used for industrial safeguarding, like copper salts, chromium plates, arsenic, etc, which are very dangerous and absolutely not ecological!

Decree No 2004-1227 of November 17th, 2004 (French Republic): " Article 1st. - Article 13 of the decree of October 2nd, 1992 referred to above is supplemented by a second subparagraph thus written:

“It is interdict to put on the market the wood treated with compounds of arsenic. ” Article 2. - Article 14 of the decree of October 2nd, 1992 referred to above is replaced by the following provisions:

“Article 14. - Notwithstanding the provisions of article 13 above, substances and preparations of protection of wood made up of inorganic solutions of compounds of type CCA (copper-chromium-arsenic) of type C can be implemented by means of processes using the vacuum or pressure for the impregnation of wood in installations declared or authorized with the title heading 2415 of the nomenclature of the classified installations. The companies which use for purposes above described of composed of arsenic are due to the provision of the administration, to be presented on any requisition of the authority qualified, the information relating to the quantities of products used and the zones of use. ”

Article 3. - He is added to the decree of October 2nd, 1992 referred to above article 14 (a) thus written:

“Article 14 (a). -

1. Notwithstanding the provisions of article 13 above, treated wood with solutions CCA under the conditions described in article 14 can be put on the market for one professional use and industrialist when the treatment is implemented to preserve the integrity structural of wood at ends of safety.

2. Wood thus treated is intended for the following uses:

- frame of public buildings, agricultural, administrative and industrial;

- bridges and works of art;

- sawlog in fresh water and brackish;

- acoustic baffles;

- avalanche barriers;

- slides and safety fences of the highway network;

- piles of fence being used for parking of the animals;

- works of reserve of the grounds;

- posts of electric drive and telecommunications;

- cross-pieces of subway.

3. To in no case wood thus treated cannot be used:

- in the residential buildings;

- in any application involving a risk of contact repeated with the skin;

- in marine water;

- at agricultural ends others that those related on the piles of fence for animals and the uses of frame or other structures aimed to the 1 of this article;

- in any application in which wood treated risk to come into contact with intermediate or finished products intended for the human consumption or animale."

the bitumen

Natural asphalt is used since mists of time as protection of the stakes of fences and of the boats, the most difficult uses of wood because the zones located between the air and water are the privileged ground of mushrooms.

paintings

Many marks propose paintings known as natural. To be able to carry this title they must contain at least 90% of natural products.

The lasures are nonfilm forming and let wood breathe. They are easier to improve and renovate that film forming paintings. The lasures carrying the codes C2 or C3 are fungicidal (except the new range of C3) and anti-blueing.

Topcoats are semi-film forming and are sometimes called glossed lasures. With code CTOP, they have a anti-blueing effect.

Film forming paintings prevent certainly water from reaching wood when they are in good state, but contribute to create the conditions of containment suitable for the development of mushrooms as soon as they present imperfections. Acrylic paintings do not penetrate in wood and can form “blisters” where water infiltrates. The oil-base paints remain longer adherent.

the varnishes

The varnish is a thick, hard and film forming layer transparent. It is used for the completion of the parquet floors, making them insensitive with the spots. But the varnish prevents wood from breathing, makes it odorless and cold. The film wears and the final improvements are visible.

Others

In the series “chemicals décriés”, one can quote the Creosote, which, after long years of service, was prohibited by the European commission, of an adopted directive on October 26th, 2001. This directive prohibits the sale with the consumers, and also applies to the wood treated with the creosote. A scientific committee of the EU indeed concluded from a recent study which the creosote has a carcinogenic potential more important than it was thought, exceeding the limits allowed under the existing legislation, in particular because of benzo-have-pyrene (BP). It is possible to continue to use the creosote for industrial applications, for example for the cross-pieces of telegraph pole and railroad, but its composition will be the more severe restriction object.

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