One may hear people expressing their opinion about the wood as a building material applying the superlative degree only. There occurs a paradox situation: some people tell about wood only good things, the other find a lot of “blurs” in it. This is the destiny of everything outstanding: talented people, great ideas, inventions, works of art, materials. Both the delight and criticism are pronounced at their address. And in the course of time the valuation may change.
It concerns also the wood. Its devotees, who irrespective of the amount of money in a purse declare: “If to build a house, then only a wooden one”. And skeptics will say: Wood? In no case! You’ll have only troubles from it”. As always occurs with extremes, the truth lies somewhere in the mid. Let’s try to find it. As usually, let’s start from the history.
From the very beginning Rus represented wooden structures and houses. There are a lot of important notions for the Russian related with this material: a staff, a village, etc. (the words that have equal root in Russian). Wood was applied as a basic building material in Northern Europe and Africa, wherever the woods were suitable for construction.
However, the largest public structures and houses of the most prominent people were erected from stone. In olden times stone-built houses were named chambers in the Rus – which was an unconditional sign of wealth and noble rank. This came to stay firmly in our consciousness.
On the other side, a paradox situation occurred, when not only new materials (for example, linoleum, finishing polymer films and sheets), and also traditional (for example, tile) imitate the structure and colour of the natural wood. This may be reasoned, for sure.
Wood devotees are not tired of admiring its natural beauty. Even the most popular pine in our civil engineering, as if usual, without any specific colour refinement, is rather beautiful.
Fresh-cut it is dark yellow in the interior, in the course of time the colour changes, becomes a little bit reddish and in 15-20 years acquires a brown and golden nuance becoming more and more saturated over the years.
Brown wooden beams, doors and other wooden elements look rather effective in the interior on the background of white plastered walls. Outside, the wooden walls acquire a silver and grey colour under the burning sun changed with rain and under the melted snow and having got wet – dark and grey, almost black colour. The Russian poet A. Block wrote that grey Russian izbas (wooden houses) for him were like “tears of the first love”. It implies that the fascination can be felt even in this “greyness”.
Affirmation that wood does not require finishing generally concerns the houses made from the very qualified material. If it is not so, the log-house intended logs or beams to be grinded and polished. Moreover, walls and floor in a bath-room, WC, kitchen should be protected from the excessive humidity, so you should provide for additional ventilation. People, especially those, who timidly take care of wood, polish it with a wax and saturate with a mordant.
Yes, walls of a log-house felled or a beam made cylinder or of due quality, are nice by themselves. But if you see in the hall, a bed-room, a cabinet, children-room only timber, sooner or later this will be bored, and you will be willing any variety. You had better think it over in advance, where you hung a picture, where a carpet or a tapestry, photos of close relatives. This will dissolve a certain monotonous nature of the walls. Furniture style is really important in a log-house.
Expensive, suitable, durable wardrobes, tables, chairs can be absolutely foreign in theses walls, stylized bench and emphasized rough “folk” subjects will match the interior because of its “simplicity”. And this is not an izba, but a house of a modern family with its own taste and habits. So, the acknowledgement that a wooden house simplifies a designer’s task is disputable. You had better consult with a specialist regarding the interior prior to starting building a house.
Let us turn to aesthetic assessments to the prosaic side of life. Which role will play the walls? A person with a technical cast of mind would say that walls bear loading from the upper parts of the building and transfer the loading to the foundation. A practical person would point out on their heat-protective functions and the most experienced in the construction wisdom would remind that walls should breath, let penetrate the air and water steams, without releasing the matter being hazardous for a human being.
Let’s keep to the order. Wood is considerably lighter than a brick and concrete, and does not yield to concrete and surpasses a brick, when it concerns the compression. If we compare the bending strength according to which rule there operate the floor and ceiling beams, wood does not yield to reinforcement and metals.
Why there is still an opinion regarding the lowest reliability of wood? First, it is binding to take into account in what plane is it loaded – along or transverse to grain. So, timber is characterized with low strength upon the grain shifting along (as firewood is split). Moreover, we often mix up hardness with the strength. Hardness of wood is really low, and from the position of woodworking it is nice: the wood is easy sawn, woodworked with an axe and a plane.
According to the volume it contains only 1/3 of the solid matter, and 2/3 account for air pores. That is why wood is a good heat insulator. So, according to its heat insulation properties, a wall made from a 15 cm wooden beam or a wooden wall 20-22cm complies with a brick-laid wall 2,5 brick (or 64 cm) thick. In our opinion, it is sin to apply any special warmth-keeping lagging similar to foam plastic or a rock-wool in a log-house. And if you adhere to electric power supply, a wooden house has a lot of “narrow” places, from where heat escapes in greater volumes than through the walls. You can and need to encase for warmth-keeping floor and ceiling, to provide a double glazing (without traditional slots) and make a vestibule (as spacemen name it, the so-called “sluice chamber”) at the entrance to the house. Good acoustics is the specific property of wood. Let’s remember that the best sound columns are still made from wood. In music instruments wood is the basic sound material – this concerns violin and piano. Ostap Bender told: “Veneer is the best sound conductor”. Actually, a house made from wood is rather resonant, sound easy spreads all over the house. For softening this effect soft furniture is placed, curtains, carpets, etc. hung. Then this house will not be “louder” the stone one.
As everything being non-ordinary, wood requires more attentive attitude. Wood gives a lot of problems when dried or getting wet. This material is in especially complicated relations with water. Getting wet wood swells, warps and when drying it shrinks and becomes cracked. In this case it may extract moisture directly from air. One may watch the similar process when sugar is getting wet, this property is known as hygroscopic property.
On the average humidity the fresh-cut timber of softwood (pine, fir-tree, etc.) account for 80-100% and less depends upon the season. It is interesting that humidity of a trunk is not equal in the cross section: it is maximum according to external rings and 30-35% in the core.
When seasoning humidity of the logs cut becomes reduced. The process of drying should be slow, the final stage thereof is especially important, when humidity exceeds the limit of 25-30%. This level is named the point of grain saturation. The matter is that the wood grains generally contain cellulose and other polysaccharides. These substances are hygroscopic owing to the specific structure of their molecular chains. They are capable of adsorbing (pull up and hold) water molecules directly from air in quantity subject to humidity and temperature.
Humidity adsorbing from cellulose molecules draws them apart, which causes wood expansion (swelling). Structure and shape of molecules and the structure of wood grains themselves is such that swelling and respectively drying-up differ according to the value in different directions. The least one is along the trunk (longitudinal direction) – not less than 1%. Increasingly greater drying-up is in transverse direction. In this case in radial direction (being perpendicular to the growth rings) – up to 3-4%, and in tangent direction (tangentially to the growth rings) – a little bit higher 4-6%. This causes warping.
Swelling and drying-up of wood occurs at change of its humidity from 0% till the point of grain saturation (25-30%). Humidity increase higher this point does not cause swelling, as humidity starts filling cells and vessels; and wood becomes heavier.
Because of hygroscopic properties of the wood its humidity is always higher 0 %. Subject to air temperature wood humidity in a residential room, which is named the roomy-dry is 8-12%.
Wood exposed to air for a long term but without any contact with water is named aero-dry and its humidity is 12-18%.
All these complicated considerations are required to clarify that the reason of wood drying-up, swelling, warping and cracking is in different humidity of wood in different parts of its volume. That is why the temperature and humidity mode of the premises, wherein the valuable and sensitive to deformation wooden articles are placed (antique furniture, music instruments) should be maximum. To a certain extend water-repelling impregnation and water-proof finishing can protect the wood from humidity fluctuation. By the way, canvas of art pieces is also subject to drying-up deformation and swelling, as the canvas mainly consists of cellulose grains. One more important conclusion: construction timber (logs, beams, boards) require be slowly dried, “held” as note specialists till acquiring the balanced humidity complying with the air parameters. In this case you’ll succeed in avoiding deformation and cracking.
Hygroscopic properties of the wood bring not only troubles but serve as a damper softening humid mode of the premises: the wood absorbs excess humidity and moisturizes the excessive dry air, so, it “breathes”.
The key thesis of opponents to this building material including for erecting cottages is: wooden structures are short-lived – they burn, rot, are stricken by insects. Even if this does not occur, wood will gradually grow old and crack. They are absolutely right. The most ancient monument survived up to now, but in duly repaired condition is the church of St. Lazar Mouromsky on Kizhi isle in Karelia built in the second half of XIV century that is, this church is more than 500 years old and Preobrazhensky cathedral built in this isle known all over the world is not even 300 years old. At the same time stone-built churches in Armenia and Georgia have stayed for more than 1000 years.
Wood is an organic material that has absorbed the solar energy. So, it is natural that it easy oxidizes secreting the absorbed solar energy. Oxidation – is not only burning, it is exposed to microorganisms, fungus and insects for feeding. Besides that direct and sufficiently fast demolition, wood gradually becomes old under the action of atmosphere factors: solar radiation, moisturizing and drying-up, periodical freezing in damp condition. In this case its structure fails both on the molecular and macro levels, it changes the colour, cracks and goes to pieces.
As in major other vivid organisms it is impossible to prevent from ageing but possible to retard premature ageing (for example, from fungus destruction) or from instant “death”, for example, fire. To prevent wood from decay, that is, from being inhabited and feeding environment for microorganisms and fungus, it is required to create the conditions being intolerable for these creatures. Fungus does not reproduce at the moisture less than 15-18%, the lack of oxygen and minus temperature available is ruinous for them too. Everything is simple here: keep wood dry and everything will be O.K. There is one more way – impregnation with substances being poisonous for fungus and microbes. Modern chemistry offers a great range of antiseptics. Usually they are applied in complex remedies composition (such as “Pinotex”, “Dufatex”) for working and toning wood. Wood impregnation with tar products, for instance creosote, is rather efficient. But this treatment is possible only for wooden structures installed outside the house: sleepers, fence columns, etc. This is simply explained: tar has a strong specific odour, and this is half the work, in large doses contact with a tar is harmful for a human being.
Opponent of the wood does not calm down: “You have forgotten about the main drawback – combustibility”. In this case he presents a list of fires that destructed the whole quarters in the past and sometimes the entire city as the strongest argument. Fires broken in Moscow and London, when the entire city was almost burnt are well known. The matter is not only and not so much in the fact that structures were made from wood, as in the fact that houses were standing close to each other, and there were no any fire-fighting means. None the less the phrase “wood easily burns” became almost the axiom. But try to set on fire a log, beam board – you will hardly be a success. The statistics tells that more than in 70% of cases the basic reason of fire is oversight: non-extinguished cigarette stub, a spark when welding, electric power short circuit. Initially curtain, dry grass, greasy cloth, etc. catches fire and then fire spreads on furniture: wood and plastic is in sufficient quantities in a modern house. Fire is equally fearful in a wooden and in a stone-made house. Let us remember fire on Ostankino TV tower and total destruction (from fire!) of two New York skyscrapers on 11 September. They were made from a steel framework. Recently steel constructions of the third traffic ring in Moscow suffered from fire.
It is reasonable to prevent wood (especially its front surface) applying a special coating or impregnation from inflammation. As a rule they are inserted in the components of the wood working means. Such kind of treatment can exclude it from the above mentioned 70% of the reasons of easy ignition. Do you remember the basic thesis of wood opponents: wood does not provide the required long-living of a building. How long a cottage or a log-house need to serve? Perhaps, we should not mix the Kremlin or Windosor castle with a summer cottage. A countryside house (summer cottage) is not erected for centuries. 100-200 years is a sufficient term for a countryside private house and it will stand, for sure this period, provided due operation.
What do we have as a result?
Wood – is a universal building material. It simultaneously and quite successfully performs the functions of a construction, heat insulation, splendid finishing and even roofing material. Wood is rather technological: easy woodworked, it is easy to construct articles and timber blanks from it, which serve for assembling a house in the easiest manner.
And, finally, timber – is one of the most ecologically pure materials:
- does not require costs of energy and raw material resources for its “production” and, moreover, releases an oxygen in the atmosphere of Earth;
- it is pleasant for an eye and creates a “healthy” atmosphere in a house during operation;
- it is easy utilized, if necessary.
Applying wood in construction it is possible to use one of the parts thereof (for instance, to finish the interior with a natural battening) or to use it simply utilitarian as a construction material (rafter, beams) or as a heat insulation material, ideal material from the sanitary and hygiene position. But a real devotee of wood will erect the whole house from this material including roofing (it may be done from chips, shingles, deal). Earlier a wooden house was build by a team of carpenters during a couple of months. Now it is the time of advanced technologies and a wooden house-building is not an exclusion.
Modern building industry treats wood carefully and skillfully. It is used the wood that earlier was not considered to be timber. Instead of different-sized there are offered the cylindered logs selected according to the size and diameter. Production of logs by gluing boards and slips with further turning is in the latest fashion. In the process of gluing wood is impregnated with antiseptics and fire retarders. Such glued elements in many respects are deprived of the main blemishes of wood (disposition to warping, drying-up, cracking, rotting and inflammation).
Companies produce not only “logs” and versatile parts, a customer receives as if a wooden constructor, applied for fast and simple assembling of a house under a design.
Hugh quality of wood as a building material is confirmed that wood is returned in the urban multi-storey construction. So, in England it is admitted by law to erect 5-storey wooden houses in cities. The new building of the Embassy of Great Britain in Moscow serves a model, whereon there are used wooden glued beams of ceiling.
Wood remains the most ancient and ever-green material and we apply to it with gratitude and real esteem.
K.Popov, professor, the chair of building materials of the MSCU after A.Tolstyh,
tech.sc. candidate. Magazine “Novij Dom”