Wooden construction materials, combining high strength, environmental friendliness and ease of installation, are widely used in modern low-rise construction for the construction of roofs, ceilings and a load-bearing floor frame. A correctly calculated distance between the floor joists and the interfloor beams is the key to the strength and durability of not only an individual structural element, but also the entire structure as a whole.
What are floor logs?
Floor joists, made of a wooden beam of a certain, precisely calculated section, are power elements that perceive static loads from furniture, equipment installed on the floor and dynamic loads that arise when people move inside the premises. Floors on wooden logs have some features that make it possible to level out minor flaws in building structures:
- Uniform distribution of the load on the underlying building structures;
- Increasing the overall strength of the floor or slab;
- Improvement of soundproofing properties with the formation of an additional heat-insulating layer;
- The possibility of laying engineering communications with a relatively high maintainability;
- Low complexity of installation, providing a flat surface for the installation of floors from sheet or roll materials and flooring from natural wood of valuable species.
Logs are made mainly of coniferous wood, the resinous nature of which provides protection from moisture and a long service life. Hardwoods with high moisture resistance or larch products with a high content of natural resins are used for the device of logs in premises that are difficult from the point of view of operation.
Why is it necessary to calculate the distance between the lags?
Like any other construction materials, wooden products have certain indicators of strength, durability, service life and, of course, prices. When arranging wooden floors on logs or interfloor beams, you can also use thick logs laid at a close distance from each other, having obtained the highest structural strength and spending a rather significant amount. But the use of the required number of lags or beams with a cross-section corresponding to the expected load will allow obtaining the necessary structural strength at much lower costs.
In a panel house, when the logs are laid on the surface of a reinforced concrete floor slab, their cross-section is chosen as the minimum necessary for fastening a floorboard or chipboard. Another thing is the use of wooden structures in a frame structure, when the logs perform the function not only of the basis for the future floor, but also serve as a structural element of the frame associated with wall supports.
Basic calculation criteria
- The thickness of the floorboard or board materials OSB, chipboard;
- Number of support points or distance between walls;
Even having such minimal data, it is possible to correctly calculate the required section of a wooden beam for the manufacture of logs and the maximum step between the logs.
Bar section
The section of a wooden beam for a lag device is selected depending on the distance between the supports and the required floor loading capacity. When calculating the required section of the lag, you should take the maximum load on the floor not more than 300 kg per m 2.
As a lag, a square or rectangular bar is used, the wider side of which is located vertically. Thus, the maximum rigidity of the log is obtained with the minimum consumption of wood, which reduces the overhead for flooring. In construction practice, the ratio of the width of the log to its height is equal to 1.5-2, which is optimal in terms of strength and cost. When using a standard edged board with a thickness of 5 cm as a log, its height with a gap between the supports of 2 m should be from 10 to 15 cm.The standard dimensions of the log, depending on the span, are presented in the table:
Sometimes it is difficult for an individual developer to find a standard timber suitable for making a log of the required section. The way out of this situation is quite simple. To ensure the required floor load capacity, several standard 5-6 cm thick boards can be installed side by side, increasing the height of the resulting timber by 1-2 cm relative to the standard one. Such a "puff pie", even in the absence of fastening the boards to each other, completely replaces a full-bodied timber of the required dimensions. Similar results can be achieved by placing the boards at equal intervals along the entire length of the supporting surface of the foundation.
The only thing that should be taken into account is that in a frame house such a method of load distribution is quite difficult to apply due to the binding of the lag to the racks of wall structures, openings and the distribution of insulation. In a frame house, floor logs are used as interfloor beams, therefore, the minimum required section must be increased taking into account the load from the ceiling structures and insulation.
Step between lags
In the manufacture of wooden floors, it is clearly traced how the distance between the lags, called the step from the thickness, and the type of materials used depends. The thicker the board used as a flooring, the greater the distance between the joists. The table below shows more clearly which step should be chosen when using different thicknesses of the board.
As a rough floor covering in modern construction, slab structural materials are often used instead of boards, which accordingly changes the calculation method. Particle board (particle board), cement particle board (CBPB), oriented strand board (OSB) and gypsum fiber boards (GVP) are successfully used as a basis for a coating of roll materials or ceramic tiles, arranged on wooden logs. In some cases, chipboard can be additionally coated with cement or gypsum-based materials. Considering the greater bending rigidity of the chipboard and the lower strength than the board, you should choose a step between the lags of no more than 40 cm, and when using a thicker chipboard (20-22 mm), increase the step between the lags to a maximum of 60 cm.
When calculating the step between the lags for a particular room, you can use the averaged tabular values, and if the distance between the last lags is less, then the strength of the floor in this place will only increase.
Consequences of calculation errors
What happens if you choose the wrong section of the lag and the step between them? When installing floors on a concrete base, the most important parameter will be the step between the lags, on which the behavior of the topcoat depends. A chipboard plate, fixed on logs installed with a larger than allowed gap, can sag or break, ceramic tiles can crack, and the board can bend. In any case, the floors will require rework.
More unpleasant consequences come from errors in calculating the required amount of lags used as interfloor floors. If a larger number of lags or a larger section of them must be used than indicated in erroneous calculations, the strength of the entire structure is significantly reduced, which can lead to irreversible deformations and complete destruction of floors.
Calculation methods
To calculate the dimensions of the timber and the number of elements required for the installation of a wooden floor on logs with rough coatings from a board or chipboard, you can:
- Contact a design organization, which at a professional level will calculate how many elements should be covered from a board or chipboard, and what size of timber should be used during construction;
- Use special averaged tables on your own, choosing which value is closer to the required one, leaning upwards, if there is no exact coincidence of real and tabular sizes;
- Use computer programs and online calculators, into which a sufficiently large number of parameters are entered, and the program will accurately determine the required dimensions of the timber and the distance through which it must be installed.
All parameters must be specified in mm
X- Floor width.
Y- Floor length.
S1- The width of the log.
S2- The thickness of the log.
S3- Distance between lags.
O1- The width of the floorboards.
O2- The thickness of the floorboards.
O3- The width of the sub-floor board.
O4- Board thickness.
R- The distance between the boards.
Using the online calculator, you can calculate:
- The volume of lag materials;
- Calculation of the lag for the floor: length, width and the required amount;
- Total floor area or square;
- Number of rows and volume of flooring;
- Number of sheets of wood, laminate or parquet;
- The volume between the lags for insulation;
- The amount of material for the sub-floor.
Useful information
Wooden flooring is made in three tiers, as shown in the picture above. At the bottom are the supporting logs, on which the roughing boards will be laid, and on top of the finishing floorboards. Below we describe in detail the installation technology.
DIY wooden floor
As a rule, these works are carried out after the end of the heating season. Since at this time, the boards will not absorb excess moisture. The weather should be dry and sunny. It is best to use an unplaned board for rough flooring. While for the final finishing layer, milled and dried boards with a longitudinal groove for ventilation are used. Boards with a curved edge for groove connections. As a rule, each such board is pre-treated with a decorative and protective compound.
During the installation process, you must follow the requirements:
- All logs must have good stability;
- Logs are laid strictly horizontally (except when the slope is provided for by the project);
- Provide ventilation under the floor;
- The moisture content of the wood should not be more than 12%.
We mark and prepare the floor surface
First of all, we mark the room, and mark the places that need to be planned in order to achieve a uniform level (taking into account the thickness of the seams and the height of the brick). For backfilling incompressible soil, fine gravel or sand is used, with a layer thickness of up to 5 centimeters.
After that, we tamp the entire surface. In those places where the logs will be located, we fill in crushed stone and also tamp it into the ground.
Installation lag
As a lag, you can use a wooden beam with a size of 50x100 mm. According to your results of the program, we carry out the installation of the timber on the already rammed surface.
If you plan to increase this distance between the lags, then in this case you should use a larger section of the bar.
If the base of the subfloor has a concrete floor or slabs, then the logs are installed directly on the concrete. In this case, you can use a smaller cross-section of the bar, since the bending load is almost completely eliminated. The rough flooring will act as a retainer for the second tier, and therefore a 50x50 section is sufficient.
The distance between the lags will depend on the thickness of the material to be coated. For example, 60 centimeters for a milling board, 40 centimeters for OSB or plywood.
When the logs are installed, we proceed to waterproofing the space under them with roofing material or other modern material.
Draft layer
When the logs are laid, we begin to install the second level, namely the "draft boards". To do this, all end joints should be performed directly in the middle of the lags. To fix the boards, we use wood screws of the required size. You can either press the roughing boards together or nail them at a short distance. In our case, this interval is determined by the value R.
Nails should be driven towards each other at a slight angle for a firm fix
If you are laying with milling boards, it is not enough to press them together with your hand. For this, special stops and wedges or tightening devices are used.
To fix the finishing board, we use nails or wood screws.
The heads of the fasteners should not be higher than the surface of the board. To do this, you need to go deeper by 2 millimeters. The indentations can be treated with a special putty before painting the floor.
If you are using screws instead of nails, you will need to drill holes and countersink each indentation afterwards.
In the process of laying, a gap of 10-15 millimeters must be left between the wall and the end of the log or the extreme boards, which will subsequently be closed with a plinth. This gap will act as a compensator during thermal expansion or moisture swelling.
The flooring is ready and can now be covered with wood stain or protective varnish.
A wooden house and a bathhouse are the dream of many townspeople. Each of those who had to build a log house with their own hands, knows perfectly well the purpose of logs and beams. These are the supporting structures of the building, therefore, the material for them, as well as their number, must be selected very carefully. Floor logs are recommended to be made of dry first-class material, treated with antiseptic and fire retardants. The most common way to install them is on beams cut into the walls during construction.
Calculations of the lag for the floor are done, taking into account the basic parameters, the lags should be 1.5-2 times higher than the height of the flooring, otherwise the nails will not be able to firmly hold the floor boards.
They are installed taking into account the fact that insulation material is usually placed between them. It can be expanded clay, polystyrene, but most often mineral wool is used, pressed into slabs 50-60 cm wide. Logs are mounted at the same distance from each other. A wooden floor is laid on them, which, if properly installed, will last for several decades. Logs are made of bars, beams, boards. They serve to redistribute loads from the floor, and are also a fixture that unites all units and parts into an integral system.
Benefits of using lag
The floor on the logs has a certain degree of functionality. In the space between them, you can lay pipes, wires, thermal insulation materials.
The bars are relatively inexpensive. Installing them is available to everyone.
These floor supports are capable of withstanding a load of 5 tons per square meter.
Figure 1. Scheme of fastening wooden beams.
When repairing a floor, it is often enough to repair a log. There is no need to re-layer the floor.The design is lightweight. The load on the floor is much less than with a cement screed.
The space filled with mineral wool will keep the house warm and protect it from unnecessary noise.
The bars allow you to bring the floor plane to any height.
The structures put in place do not require additional work. You can install the flooring immediately.
Disadvantages of the floor on the logs:
- The room loses several centimeters of height.
- High labor intensity. It is required to carefully mark and align all structural elements.
Calculation of some lag parameters
The calculation of the lag for the floor is made taking into account the basic parameters. The lags for the floor should be 1.5-2 times higher than the height of the flooring, otherwise the nail will not be able to firmly hold the floor boards. If the thickness of the floorboard is 50 mm, then the height of the planks should be about 100 mm. If the subfloor is made of plywood or other sheet material with a thickness of 20 mm, the beams can be significantly lower, 30-40 mm.
The material for the manufacture of wooden logs should be chosen from conifers. The moisture content of the workpieces should not exceed 20%. The cross-section of the bars is selected rectangular. They can be cut from a board 50-60 mm thick. Finished products are laid across the light coming from the windows. The laying step is from 40 to 70 cm. Knowing the laying step and the size of the room, it is easy to calculate the required number of elements. Before installation, all wooden elements are treated twice with an antiseptic compound. The antiseptic can be replaced with regular hot bitumen.
Figure 2. Adjusting sleeves. They are used to level floors on joists.
In practice, very often the height of the lag is chosen taking into account the thickness of the insulation layer. As insulation for the floor, mineral wool is usually used, produced by slabs, the thickness of which is 50 mm. The joists for the floor should be of the same height. If it is decided to lay the thermal insulation in a double layer, then the bars are needed with a height of 100 mm. The distance between them depends on the thickness of the subfloor material. The thinner the rough flooring, the more often logs are installed. With a thickness of plywood that can be used as a backing for finishing flooring, 12 mm, the gap between the bars is 30 cm.
Most often, the subfloor is made of a grooved board. Boards should be spruce, pine or fir. They are not suitable for a finished floor, since the wood is very soft, even traces of thin heels remain on it. It is imperative to lay a laminate or other topcoat on top. The thickness of the boards with a normal pitch of 50 cm is recommended at least 35 mm. In most cases, the calculation of the pitch of the bars is carried out taking into account the thickness of the floor material:
Figure 3. Fasteners. It is used for fastening wooden structures.
Board thickness (mm) - lag step (mm):
- 20 – 300;
- 24 – 400;
- 30 – 500;
- 35 – 600;
- 40 – 700;
- 45 – 800;
- 50 – 1000.
For the manufacture of these parts, not only wood is used, but also reinforced concrete, various polymers and metals. Reinforced concrete products are highly durable. They can be used when building a house outside the city. The rest of the materials can be used when repairing floors.
If the base of the floor is wooden beams, the joists can be installed by attaching them to the side using self-tapping screws (Fig. 1). The size of the fasteners should be 2.5 times the thickness of the bar with a diameter of 6 mm. The positive aspect of this method is that when adjusting the height of individual logs, no additional adjusting pads are required.
In construction, special wooden or plastic products are sometimes used that have holes into which small plastic adjusting bushings are inserted. They contribute to the rapid leveling of the surface formed by the lags. Such products are installed very quickly and do not require the use of pads (Fig. 2).
Figure 4. Floor mounting scheme on joists.
Before installation, wooden elements must be protected from various microorganisms and wood-boring pests by treating the material with a disinfectant, then a water-repellent compound.
In rooms with low ceilings, it is better to use other methods of floor installation. When performing the calculation, one must not forget that the bars reduce the size of the room in height by 10 cm or more.
Floorboards or subfloor sheets should be attached to each joist.
The ends of structural elements should not touch the walls of the building. There must be a gap of at least 5 cm between them.
Instead of a certain section of a wooden beam, you can use boards connected in pairs to each other and reaching the size of the desired beam in diameter. Somewhat larger sizes are not prohibited. The boards are installed on the edge.
The logs can be attached to the concrete base with special galvanized metal corners, which are fixed on the base using dowels and self-tapping screws. Instead of corners, U-shaped devices are often used (Fig. 3).
If necessary, the bars from which the logs are made are joined to each other to achieve the desired length. There must be a solid support under the joint. This support is often a brick pillar. Under its construction, you need to dig a hole about 10 cm deep. It is covered with sand and watered abundantly with water. Cover the sand pillow with a layer of polyethylene. A cement-sand mortar is placed on it and a column of red brick is laid out.
You can lay out the columns in rows and fix the logs on them (Fig. 4). The size of the columns is 25x25 cm. The calculation of the number of bricks is not difficult.
The construction of the floor on the joists allows you to immediately mount the rough and final flooring.
Lags can be made from various materials. Most often, a wooden block or board is used for their manufacture. And there are a lot of materials for finishing. Their choice depends only on the preferences of the owners and the contents of their wallet. A plan of rooms with precisely specified dimensions, made on paper, will help to calculate the materials for making logs for the floor. All calculations are best done before starting the basic installation work.
Before buying a floorboard, you need to calculate how many cubes of sawn timber are needed for a particular design. At the same time, an accurate calculation can be done using a conventional calculator, knowing the area of the room and the thickness of the board. Such skills will be useful to you not only in order to calculate the volume of lumber for flooring, but also if you decide to build a house, because wood products are used for the construction of various structures.
Since the price of all lumber on sale is charged per cubic meter, it is important to be able to calculate the need for this particular unit of measurement. This is how not only the number of boards is counted, but also other sawn timber, for example, timber, slats, etc. The thing is that products with the same section may differ in length. Therefore, after determining the volume, you can understand how many floorboards there will be in one cube.
It is important to know: when buying a board made of valuable wood, the products are sold per piece. The thing is that the price of such coatings is too high, and when calculating in cubes, there is a small error.
When calculating, it is better to use a regular calculator. So you can get a more accurate result and take into account all the nuances of the future design of the house. Although if you need to find out how many cubes of a board, for example, 50 mm thick, will be needed for flooring, you can also use an online calculator. He will be able to perform such a simple calculation correctly. However, it is always helpful to be able to count the amount of lumber by hand.
When building a house or laying a floor, the calculation is carried out in the same order:
- First, you need to calculate the total volume of lumber in cubes. Knowing the moisture content of the wood, you can determine the weight of the entire material. This will help you decide which shipping method to use for your items.
Advice: when ordering a carrier, it is better to indicate an overweight (10-15% more). So you will not have problems with the cargo, because the moisture content of the wood declared by the manufacturer may be slightly more or less.
- Further, knowing the dimensions of the boards, you need to calculate the volume of one element. Then you can find out how many products will be in a cube. By multiplying this number by the number of cubes, you will get the total number of floorboards for your floor structure.
However, such a simple calculation is applicable for edged elements, because they are processed from all sides and when they are stored in a pile, there are practically no gaps left. To calculate how many cubes of unedged boards are needed for flooring, you will have to use a correction factor, because due to the untreated sides of the product, there will be too many gaps left when stacked in a stack.
Calculation example
Suppose that in a house you want to cover a room with a size of 5x6 m with a floorboard 50 mm thick.Calculation of the volume of lumber and the number of products is carried out in the following sequence:
- We find the area of the room: 6x5 = 30 m².
- Since we decided to use a board with a thickness of 50 mm or 0.05 m, the lag step can be made 1 meter.
- Knowing the thickness of the element and the area of the room, we get the volume of lumber: 30 m² x 0.05 m = 1.5 m³.
- Now using the calculator, you can calculate how many floorboards you need. For this, knowing the dimensions of the floorboard, we calculate its volume: 2m x 0.05 mx 0.13 m = 0.013 m³. Now we divide the total volume of lumber by the resulting number for an element with a thickness of 50 mm: 1.5: 0.013 = 115 boards.
Thus, using a regular calculator, you can calculate the need for other lumber for building a house: lining, timber, slats.
Edged boards are in greatest demand in the sawn timber market. Their distinctive feature is four-sided processing and removal of edges with tree bark. The high demand for this type of building materials is explained by their practicality, durability, environmental friendliness and ease of use.
The main areas of application of edged boards are construction and furniture production. In construction, this material can be used for laying floors, ceilings, walls and stairs. In furniture production, boards are used to create solid wood furniture.
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- Calculate the surface area to be covered (eg 10 * 10 = 100 m²);
- Calculate the area of one board (for example, with the parameters of the board 20cm * 5cm * 2000 cm, the area of one will be equal to 0.2m * 2m = 0.4m²);
- Divide the surface area by the area of one board (100 m² / 0.4 m² = 250 pieces).
To calculate the number of boards when buying in cubes, you must:
- Calculate the required number of boards (divide the surface area by the area of one board);
- Calculate the required cubic capacity by multiplying the parameters of the board by the required amount (for example, you need 20 pieces of boards with the parameter 20cm * 5cm * 2000cm, which means the required volume is 20 * 0.2 * 0.05 * 2 = 0.4 m³). In this case, all values must be converted from centimeters to meters.
Types of boards
There are several types of boards that differ in purpose and technical characteristics. Depending on the degree of humidity, there are:
- Raw - boards of natural moisture. It can be used in the construction of low-critical structures.
- Dry - industrially dried. Drying is carried out to avoid deformation of the board and to prevent rotting.
Depending on the quality of the boards, the material is distinguished:
- Selected grade - used in the automotive and shipbuilding industries;
- The first grade - in addition to shipbuilding and the automotive industry, is used in construction and furniture production;
- Second grade - used in the same areas as the material of the first grade;
- The third grade is the production of furniture and packaging products;
- The fourth grade is used for the production of containers and packaging.
By the type of cut, the boards are divided into:
- Radial - the saw cut passes in the middle of the trunk, at an angle of 90⁰, due to which the material has high strength and moisture resistance;
- Semi-radial - the cut passes at an angle of 45⁰, the material is of the middle price category;
- Tangential - the most economical type of sawing, boards of this type are more susceptible to moisture. Drying deformation is possible.