Wood is one of the most expensive building materials in the estimate, and, therefore, mistakes made when purchasing it will be very expensive. If you have entrusted the construction of the roof to an experienced specialist, then it makes sense that he is the one who is engaged in the selection and purchase of wood.
If you have to personally evaluate the quality of wood and make a purchase, then you need to know how to choose it in order to avoid many misunderstandings.
Wood can be purchased in three main ways:
wood in cubic meters,
cut to size wood
finished truss structures.
Let’s take a closer look at each procurement method.
Wood in cubic meters. This purchase method is the easiest. By contacting a warehouse, a mill or a specialized company, you can purchase wood, indicating the required volume (cubic meters) of slats, beams, boards. In this case, wood processing is carried out directly at the construction site. The carpenter will cut, process and assemble the necessary elements for the construction of the roof from the purchased material.
With this method of procurement, it is difficult to control the quality and moisture content of the wood. When processing wood at a construction site, it is difficult to guarantee the high quality of the treated surface (cutting, grinding, impregnating), moreover, a lot of waste remains. Please note that when buying wood in cubic meters, it is necessary to purchase 10% more than indicated in the project, since the margin for pruning and various waste must be taken into account.
Wood after pruning. In many woodworking plants and companies, you can buy cut-to-size and prepared wood. In this case, at the construction site, the carpenter performs only the connection of wooden elements, which greatly reduces labor intensity, increases the speed of work and reduces the amount of waste. At the time of ordering timber, in order to order the required quantity and the required length, you must have on hand a specification of the structural elements of the roof, indicating the exact dimensions and quantity of all its elements.
This specification is very rarely attached to a house project, so ask your contractor or designer to put it together for you. Never forget that the purchase of wood for roofing is a very important and responsible step. Even if the purchased tree will be knocked down, cut or assembled from it directly at the construction site, it must still be properly dried (moisture level 15 – 20%), have a smooth and even surface, treated with special fire-fighting, insecticidal, fungicidal and by other means. The purchase and use of unprepared or poorly prepared wood can lead to a decrease in its strength, reliability, durability, as well as various irreparable consequences, up to the complete destruction of the roof structure.
Finished roof structures. Not so long ago, some companies began to offer ready-made roof structures for private developers. Mounting these truss trusses on the walls has become much faster and easier than knocking down a structure from individual elements. It is now possible to assemble the roof structure in just 1 to 3 days without the need for a carpenter.
These truss structures are much better, since the fitting and trimming of various elements is carried out using special electrical equipment in production (in the industrial workshop).
In this case, you do not overpay money for unnecessary waste, but you will have to spend a lot for convenience and quality. When ordering a finished roof truss structure, the manufacturer will first send a specialist to the construction site to measure and clarify the roof structure according to the design documentation. Before choosing a manufacturer for the truss structure of your house, find out more about it, about the projects it has completed, about its production facilities and the equipment used.
It would be nice if the selected lumber company, in addition to rafters, would supply wood to various flooring and window manufacturers. Find out if the company has drying kilns, impregnation devices, modern saws, etc. All these factors affect the quality of the wood they offer.
After choosing the method of purchasing wood and the direct supplier, you need to decide on the right time to order it. So the right decision would be to supply wood to the facility just before the start of the installation of the roof. You can order it earlier, but at the same time agree on the time of its delivery. Due to the fact that the wood will be delivered to the construction site at the last moment, you will not expose it to adverse weather conditions or look for a special covered room with optimal humidity for its storage. Do not forget about the delivery time, which, depending on the chosen method of purchasing wood, will vary from 2 days to several weeks.
So, depending on the degree of preparation of wood will be:
for the purchase of wood in cubic meters and cutting it directly at the construction site – 2-7 days, but do not forget that wood processing before installation will also take some time,
when purchasing processed and cut to size wood – less than a working week,
when ordering a finished truss system – about 1.5-2 weeks, since time is needed not only for delivery, but also for individual design and manufacture.
When choosing wood for the construction of a roof truss system, in addition to the aspects discussed above, a number of questions may arise related to the choice of section size, wood species, wood type, humidity, use of impregnation, etc. What kind of wood should be for the roof? ? The answers to these questions should, first of all, contain a correctly drawn up project of the house.
It should detail the following points:
type of wood of the roof truss system,
section, length and dimensions of all structural elements of the roof,
ways of connecting its elements,
the estimated amount of wood needed to build a roof (usually in terms of volume). The size of the section of wooden elements. Depending on the section and size, wooden elements can be called a beam, beam, rail or board.
For the construction of a roof frame, any of them may be needed, but tetrahedral bars and boards are most often used. Tetrahedral bars generally have a width of 10 to 20 cm and a thickness of 5 to 20 cm. Basically, they have a rectangular or square section. Tetrahedral beams are used as posts, rafters (including supporting ones) or Mauerlats.
Boards. As a rule, the board has a width of 10 to 20 cm and a thickness in the range of 2 to 5 cm. In most cases, the boards are used as fastening elements of the roof structure (ridge or wind boards). The entire roof frame can also be made from them. The frame of the boards is mainly constructed in buildings with a non-residential attic or in the construction of frame houses.
The type of tree. Coniferous trees are usually used as wood material for arranging the roof: spruce, pine, larch. This wood is light and soft in processing, has a small number of knots, and also has high strength.
Sort. All coniferous wood, according to the generally accepted classification, is divided into 5 grades (from 0 “Extra” to 4). The grade of wood, first of all, depends on the presence of various defects in its structure, such as blue, rot, stains, cracks, knots. Purchased wood should not have a large number of defects, as they affect its strength. Roof structure elements, such as puffs, are made exclusively from grade 1 wood; racks and rafter legs – from wood of 1 and 2 grades; struts and various non-bearing structural elements – from grade 3 wood.
Adhesive bar. In some cases, glued wooden beams are used instead of solid wood. The use of this timber is determined by its resistance to deformation and high strength, but at the same time, its cost is usually 2-3 times higher than a solid wooden array. So, for example, glued laminated timber made from grade 3 wood has the same strength characteristics as solid wood grade 1. Basically, glued timber is used as a truss structure in the construction of roofs with increased resistance to deformations and loads, in the construction of frame houses, and also in cases where long and strong elements are needed, which cannot be made from solid wood.
Humidity. When choosing wood for the roof structure, pay special attention to its moisture content.
So, it is recommended to use wood of the following moisture content for roof structural elements:
no more than 15% – for roof elements that will be additionally sheathed on the inside (for example, clad with plasterboard boards),
no more than 20% – for open roof elements (roof over an open balcony, terrace, canopy rafters, etc.).
Please note that the strength of wood with a moisture content of 30% is almost 1.5 times lower than wood with a moisture content of 15-20%. Among other things, products made from damp wood can easily “lead”. Wet wood can be dried at home using the natural drying method. To do this, it must be laid out on a flat surface in a dry and warm place and kept for a year. Since this method requires a lot of time, the drying of wood on an industrial scale is carried out forcibly in special closed drying chambers at high temperatures.
During the drying process, the wood retains its shape and is sterilized, mold spores, fungi, and insect larvae die inside it. When purchasing wood, ask the seller to measure the moisture content of the offered wood in your presence. Impregnation. The wood purchased for the rafter system must be impregnated (treated with a special impregnation).
The most common method of wood impregnation in vacuum. In addition, wood impregnated by immersion in a bath is sold. You can also process wood yourself by applying impregnation to the surface with a brush, sprayer, or by immersing wooden parts directly into a container with impregnation. The type and method of impregnation (fire-retardant, moisture-proof, biological), as well as the specific brand of impregnation, should be indicated in the project documentation for your house.
If you are buying wood that has already been processed, then you must ask the seller for a confirmation document about the method and method of impregnation, the brand and name of the product used. The quality of the impregnation can be easily checked by making a cross cut, which will visually show how deeply the impregnation has penetrated into the wood.
When performing impregnation on your own, you must strictly adhere to the recommendations indicated by the manufacturer of the impregnation on the package. Please note that wood planed on four sides, compared to unplaned wood, is more resistant to fire (the flame slides along the smooth, even surface of the wood without burning it) and to pests (it is more difficult for insects to penetrate through a smooth treated surface).
Transportation. When buying wood, it is necessary, if possible, to look for a supplier located not very far from the construction site, since you will have to pay extra for delivery. In addition, in case of a shortage of material, it can be quickly and easily purchased. The cost of delivery can also be affected by the capacity and carrying capacity of the vehicle. Pay attention to the fact that during transportation all wood is reliably protected from direct sunlight and precipitation.
The ideal option is transportation, in which the finished parts of the roof truss structure will be placed in the car body in the position and sequence in which the installation will be carried out.
Warehousing. When warehousing at a construction site, a flat, dry place must be chosen. It is strictly forbidden to lay wood directly on the ground. First, transverse wooden beams are laid out on the surface of the earth at a distance of no more than 1.5 meters from each other, and only wooden elements of the roof structure (beam, boards) are laid out on them. When laying boards or beams, each row must be shifted with planks. In some cases, a row of wood is laid across the previous one. If the installation of the roof will be carried out from the finished elements of the roof structure, it is recommended to build it directly from the car body, without shifting or storing them.
One of the main questions of the developer is: “How much can timber for a roof cost?”
Of course, there is no unequivocal answer to this question, since everything depends on the design of the roof, its area and the complexity of manufacturing, the type of elements, etc.
Below we present the notional value related to timber volume units, which will differ significantly depending on the method of timber procurement. So, when buying wood in cubic meters, the price depends both on the length of the elements, grade and species, and on the degree of processing. Wood from a tree of valuable species can cost 2-3 times more than ordinary wood.
The average price for an unedged 6-meter board is approximately 700 UAH/m3. When purchasing a board planed on four sides and dried in a chamber, depending on the length and section, you will have to pay about 900 UAH / m3.
If you order elements processed and already cut into the required size, then their cost can be approximately 1200 UAH/m3. If you order a finished roof truss structure, its cost will be calculated individually, depending on the design features of the roof.
Approximately 1 m2 of such a roof area can cost from 150 UAH. If we assume that the roof area is 200 m2, then even the cheapest version of such a roof structure will cost the owner at least 30,000 UAH.
To this amount, it is also necessary to add the cost of installation work, which usually ranges from 30 to 40% of the cost of the structure. If you purchase wood that has not been impregnated, then you must additionally take into account the cost of this treatment, which can be about 6 UAH/m2.
When purchasing wood for the construction of a roof, it is necessary to strictly comply with the requirements of project documentation, since not only the strength of the roof, but the durability of the entire building depends on the quality and reliability of the truss structure.