How thick should the floor joist be? How to calculate the distance between floor joists. Technology for self-production of logs and selection of wood

Thanks to environmental cleanliness, aesthetics, naturalness, warmth and comfort in the home, wood floors have not lost popularity to this day. When choosing them, many questions arise - what should be the distance between the floor joists in wooden house, what material to choose, how to install correctly, etc. This article will answer all your questions.

Choosing timber for logs

1. Select material from coniferous wood, the price of which is low - spruce, pine or fir. If the room is damp, purchase larch slats. It is more expensive, but it almost does not rot from exposure to moisture.
2. To save money, you can purchase grade 2/3 lumber with a moisture content of 18/20%.
3. The beams must have a rectangular cross-section. At the same time, their height should be 1.5/2 times greater than their width. Having such a cross-section, the logs will operate optimally, withstanding high loads.
4. The dimensions of the beam must be selected based on the span, that is, the distance between the beams of the lower frame. The thickness of the insulation used is also important.

Below are the sections of the logs (with a step between them of 0.7 m) for different spans.

1. When the span width is of an intermediate value, you need to choose the closest option, taking into account the safety margin.
2. When purchasing timber, inspect it for defects. Before calculating floor joists, take into account their margin of 10/15%.

Note! To protect wood from harmful insects, mold and fungi, it must be soaked with an antiseptic. The underside of the beams must be treated twice, allowing the first layer to dry for 4/5 hours.

How to determine the pitch between joists

This value depends directly on the thickness of the floor covering.

Table you can use

When thick boards with good strength are used for flooring, logs can be installed relatively rarely. If the finishing coating is thin, the timber must be positioned frequently. Below is a table of distances between floor joists based on the thickness of the boards.

To more accurately determine the step between the lags, you will need to carry out calculations.

Calculation example

1. Let the length of the room be 11 m.
2. The width of the beam will be 0.15 m.
3. We will choose floorboards with a thickness of 25 mm (0.025 m) for flooring. Therefore, the gaps between the logs should be from 40 to 50 cm. Let’s average these figures to 45 centimeters, that is, 0.45 meters.
4. Let's denote the number of lags as x.
5. The width of all our logs will be equal to 0.15∙x.
6. The first beams will be installed at a distance of 30 mm (0.03 m) from the walls. Based on this, the step between the lags will be: x-1. The distance between all lags will be equal to 0.45∙(x-1).

To find out the distance between the floor joists, we create the equation:

length of the room = width of the beam + gap between all the joists + distance from the walls.

1. We substitute the values: 11=0.15∙x+0.45∙(x-1)+0.06.
2. We solve the equation:

11=0.15∙x+0.45∙x-0.45+0.06;

11=0.6∙x-0.39;

1. The number of lags must be an integer; based on this, we round the value to 19.
2. The sum of all the gaps between the logs will be equal to 11-0.06-19∙0.15=8.09 meters.
3. We divide this figure by the number of distances - 8.0919-1=0.4494.
4. The result obtained: the exact distance between the floor joists should be 44.94 centimeters.

Frame installation

Floors with joists can be installed both on the floors of the house and on the ground base.

Installing joists on wooden floors

1. The logs must be fixed to the strapping beams. It should be taken into account that they are unlikely to have an absolutely even level. Therefore, it is best to attach the timber to the sidewalls of the beams.
2. IN in this case Determine the horizontalness of the lag using a control strip; pads do not need to be used.
3. Fix the logs with screws with a diameter of 6 mm. They should be 2/2.5 times longer than the width of the beam.
4. To prevent the lumber from cracking, drill holes in the joists and beams. In this case, use a drill that will have a diameter 2.5 mm smaller than the size of the screw.
5. When the beams are located far from each other, you need to install double logs. First, lay the first row of joists on the beams, and on top of them, with smaller steps, another one.

Laying timber on the ground

1. First, level and compact the soil with your own hands. This work can be done using big log. Nail a board to it from below and, moving the tamper along the ground with a partner, compact it. The board should be at least 5 cm thick and slightly larger than the cross-section of the log.
2. Next, mark the support pillars for the joists. When the supports for the frame are the beams of the lower frame, marks can be left directly on the beams. If the support is a grillage covered with roofing felt, place marks on the waterproofing material.
3. The distance from the initial logs to the walls should be 3/20 cm.

Before installing the support posts, you need to make a foundation for them. It can be poured separately under each support or placed under a row of posts.

The dimensions of the foundation for the column are minimum 0.4×0.4 m, height 0.2 m, 5 cm of which should protrude from the soil.

The instructions for arranging the foundation are as follows.

1. Set aside 0.2 m from the log axis marked on the strapping beams in both directions.
2. Pull the string between the marks.
3. Perform a similar operation in a plane perpendicular to the joists to mark the corners of the posts located at the intersection points of the cords.
4. Drive stakes into the corners. Next, remove the cords.
5. When the foundation is laid under a row of supports, only the edges of the row are marked with cords.
6. In the marked areas, remove upper layer soil. Compact them, pour in crushed stone and compact it.
7. Assemble the foundation formwork, which has a height of 0.1 m.
8. To waterproof concrete, place polyethylene film in the holes. If the soil is clay, then you don’t have to do this.
9. Reinforce the foundation with a frame welded from rebar, 0.8 cm in diameter. It should be laid slightly below the center of the future concrete layer.
10. Next, fill in the solution. Its composition should be the same as for the foundation of the house.
11. Allow the concrete to set for 2/3 days.
12. After this, lay the waterproofing. For this purpose, cut pieces of roofing felt according to the size of the supports, in other words, 40x40 cm. You can also make overlaps of 1 centimeter. Lay the insulation directly on the mortar; there is no need to coat it with bitumen.
13. Now you can start laying bricks. Two rows of them in height are enough, the top one should be oriented perpendicular to the length of the beam. To fasten the material, use sand-cement mortar, brick use grades not lower than m-100.
14. Lay waterproofing along the bricks.
15. Place soundproofing pads on top of it. To prevent them from moving, secure them.

First, lay the lighthouse logs, the first from the walls. Secure them at intervals of 2 meters from each other.

Note! Check that the material is laid horizontally relative to the ground, as well as to each other. If the logs lie unevenly, the protruding areas can be removed with a plane, and pads can be installed under the sagging parts. It should be taken into account what maximum deviation is permissible - it should be one millimeter per 1 meter of timber.

Conclusion

The strength and reliability of the structure of all floors depends on the pitch of the joists, their cross-section and the wood used. Therefore, you need to take the choice of these parameters seriously. In the video presented in this article you will find Additional information on this topic.

When I determined the distance between the columns for the logs, I was guided by some article from the Internet. The same article recommended taking into account the option of laying insulation between the joists. After all, with a floorboard thickness of 35 mm and the expected width of the carpet mineral wool 60 cm (120/2). The distance between the lags was chosen to be 58 cm (2 cm for cotton wool compression). Considering that the log itself has a width of 7.5 cm, the distance between the axes or centers of the columns was 65.5 cm. In older paper publications, these distances are slightly different and I have not seen a clear calculation anywhere.

In preparation from skinny concrete brick columns are laid out with a pitch (along the axes) of 0.7...0.9 m and with a distance between rows of 100...120 cm. Two layers of roofing felt or roofing felt and an antiseptic wooden lining 3 cm thick are laid on top of the columns (Fig. 7.24). The logs are supported on them, and a plank floor is laid on top of the logs.

Rice. 7.24. Cold floor with warm underground
1 - base; 2 - waterproofing made of two layers of roofing material; 3 - lower trim;
4 - top harness; 5 - external cladding tongue and groove boards;
6 - non-ferrous metal plate with holes; 7-outer wall made of boards;
8 - plaster; 9- plinth; 10 - plank floor; 11 -lag; 12 - brick column;
13 - antiseptic wooden lining; 14 - underground

HA. Stern. Carpentry work. Stroyizdat 1992

Under the logs resting on brick pillars, to ensure waterproofing, you need to place scraps of roofing material, which also protects the wood from mold.

Plank floors laid directly on the beams if their pitch is relatively small. If the beams are sparsely spaced, logs are additionally laid on them with the required spacing, and a plank floor is already laid on them. The logs are placed at a distance between the axes of 800-850 mm for boards with a thickness of 35-40 mm. With thicker boards, the lag pitch can be increased to 1 m, with thinner ones - reduced to 500-600 mm. The humidity of the boards should not be higher than 12%.

A wooden floor must have a zero slope, so beams and joists must be constantly checked using a level or level along and across the room. The pitch of the columns depends on the thickness of the logs - with a thickness of 40 mm - up to 900, with 50 - up to 1100, with 60 - 1200-1300 mm. The pitch of the posts in the transverse direction depends on the thickness of the floorboard.

Construction of a house from foundation to roof

The maximum distance between rows is selected from the cross section of the log. I used the Calculator to calculate the load-bearing capacity of single-span wooden beams" → (download). For a 150x75 log, it turned out to be more than 2.5 meters, but the width of the entire room is 6.2 meters. Hence the distance along the rows is about 2 meters

In general, of course, longer distances can be taken, but then there is a greater likelihood of all kinds of deflections and creaks occurring. Much depends on what will subsequently stand on this floor, whether the future residents will put some kind of piano or a tub with a palm tree and whether the floor will become curved or creaky.

A wooden floor in a house is always beautiful, aesthetically pleasing, environmentally friendly and healthy for all household members. However, laying the floorboard must be done correctly, otherwise the floor may soon fail, namely:

• Change the geometry of the flooring;
• To dry out or rot;
• Make the room cold and uncomfortable.

Floor joists: dimensions, installation

Logs are long bars of a certain cross-section and made of various materials. In construction, you can use a support made of metal, plastic, reinforced concrete or a compound containing synthetic resin. However, most often craftsmen use wood logs due to their reasonable cost and fairly good technical characteristics.

Wooden floor joists can be made from various coniferous species wood or more moisture-resistant larch. The latter is considered the most durable and durable material for making timber.

Important: grade 2 or 3 timber can be used as a floor joist. This will not affect the quality of the wood floor lathing in any way. But you need to pay attention to the moisture content of the board Special attention. Since material with a moisture content above 20% is at risk of shrinking and drying out during its service life. Is it necessary to talk about what will happen to the floor then?

What are they needed for?

Laying wooden beams as lathing under the future floor allows you to strengthen the entire floor structure as a whole. In addition, noise and heat insulation materials are placed in the distance between the joists, which greatly improves the characteristics of the floor.

Properly installed beams and the distance between them ensure sufficient ventilation of the underground space of the house, which means that the wood will not rot over time. Especially if the building is located on a plot with high location groundwater. How to install logs correctly and calculate optimal distance between the beams of the sheathing, we consider below.

Calculations of log installation parameters

First you need to choose the right lag section. Since they are the ones who will be load-bearing structure, which will be subject to subsequent load. Thus, it is worth making sure in advance that the finished floor can withstand both the weight of the furniture in the house and the weight of all household members. Therefore, the fastening of floor boards must be done exclusively correctly.

The cross-section of the wooden beam should be larger, the wider the span of the room for laying the floor. Thus, it has the most common relationship among craftsmen between the thickness of the lag and the width of the span (that is, the distance from wall to wall along which the lag beam will be laid):

• For 2 m, a beam with a section of 110x60 mm will be sufficient;
• For 3 m - 150x80 mm;
• For 4 m - 180x100 mm;
• For 5 m - 200x150 mm;
• For 6 m - 220x180 mm.

Thus, we see that the longer the lag is, the larger its cross-section should be. This will strengthen the entire floor structure made of wooden planks.

As for the length of the logs, it is best to order here solid beams in such a way that when laying them at the ends they recede from the wall by 3-5 mm. This approach to laying the lathing will prevent possible deformation of the floor during its operation.

If it is not possible to obtain solid logs of the same length, then when laying the beams they resort to splicing them. To do this, it is necessary to install a brick (cement) pedestal or other type of support under the splice points. In this case, the place of splicing should be strictly at the fulcrum point, and the edges of both beams should overlap each other by at least half a meter. If necessary, you can use galvanized strips to fasten and splice the joists.

Important: logs must be attached exclusively to the waterproofing layer. This way you can further protect the boards from rotting. And in the distances between the beams you can lay thermal insulation material. And for your information: it is not prohibited to use logs of larger cross-section. This will only strengthen specifications finished floor.

What should the lag pitch be?

This question is very important when installing floor boards. And professionally calculating the distance between the laid subfloor beams is not at all difficult. It (distance) directly depends on the thickness of the floorboard. That is, the thicker the floorboard, the wider the step between the joists can be made. Below is the optimal relationship between the pitch of the timber and the thickness of the floor board used.

• With a board thickness of 20 mm, the step between wooden supports will be 30 cm;
• With a floorboard thickness of 24mm, the distance between the beams is 40 cm;
• Board thickness 30 mm - pitch 50 cm;
• Thickness 35 mm - pitch 60 cm;
• Board thickness 40 mm - distance between logs 70 cm;
• Board 45 mm - distance between beams 80 cm;
• Board 50 mm - pitch 100 cm.

How to install logs?

If you undertake to lay the sheathing and floor boards yourself, then prepare in advance. Namely, in addition to beams and floor boards, prepare necessary tool and adjustable support elements. They are the best option, since they allow you to install logs on a cement base with perfect evenness.

Do not forget to additionally secure the beams against the walls during installation using a hammer drill and galvanized corners. If the logs will be laid on wooden beams, then they must first be treated with an antiseptic, and the holes for fasteners must be drilled in advance. This simple action will prevent the timber from splitting when connecting it to the beam using a dowel.

Attaching the floor board

So, all you have to do is attach the floor board to the joists. Here you need to follow some recommendations and then your wooden floor will be reliable, strong and stable under maximum load.

1. Boards are attached to wooden beams using nails, the length of which is twice the width of the board.
2. Before you start laying the boards, you need to prepare holes for fasteners by drilling. It is important to make the holes 1-2 mm smaller than the thickness of the nail. This will prevent the floorboard from splitting.
3. Ideally, the length of the boards will clearly fit into the parameters of your room and you will not have to splice the floorboards. But if, nevertheless, it was not possible to find a board of the required length, then the two boards need to be joined directly on one of the floors. This will prevent the floorboard from bending over time.
4. It is necessary to attach floor boards to all joists.
5. Ready flooring must be treated with a special varnish or drying oil.
6. We close the joints of the wall and the floor with a beautiful wooden baseboard or lath.

Important: the boards can be secured to the beams with self-tapping screws either at an angle of 45 degrees, or with subsequent treatment of the caps with a special sealant. And when laying floor boards, do not forget to leave 1 cm between the walls and the floor covering.

Owners of private housing continue to willingly choose multi-layer wooden structures, despite their not very long service life. After all, they are characterized by environmental friendliness, light weight and relatively low cost. But if, during the construction of walls, various types of wood successfully compete with artificial materials(brick, foam concrete, gas silicate blocks), then when arranging floors, the predominant material for floor joists is still wood. However, in the manufacture of multilayer structures made of wood, not only wooden joists, but also made of durable polymers.

• What are lags?
• Functions performed by lags
• Choosing material for logs
• Impregnation for wooden floor joists
• Section and dimensions of the logs
• Step between joists

What are lags?

This term refers to transverse or longitudinal beams, laid on the base of the room. Boards are already fixed on them, forming a horizontal, flat floor surface.

Joists can be used regardless of what material the floor base is made of:

• concrete slab;
• floor beams;
• even ordinary soil.

All options use approximately the same design, the differences are only in the methods of attaching the logs.

Functions performed by lags

• Create a flat horizontal surface for the floor.
• Distributes the load on the foundation more evenly.
• Leave an air gap between the base of the floor and its finishing coat. This space is usually used for laying communications, and sometimes even for storing certain items.
• Most often, the space between the lags is filled with sound and heat-insulating material, making the room noticeably warmer and quieter.
• A rotted or cracked joist can be quickly replaced with a new one without affecting the base of the floor.

Choosing material for logs

When deciding which logs to choose, you need to remember what properties their material should have:

• evenness;
• strength;
• minimum deformation at rated load.

When deciding which joists to use for the floor, you need to keep in mind that they can be made from: various materials, the most traditional of which is wood, although the choice of floor joists can also be reinforced concrete, metal or plastic. Adjustable structures made from metal channels or reinforced concrete are also found, although not often. With the help of especially strong joists permissible load on the floor can be increased several times. Most often, such elements are used in the construction industrial buildings or public premises.

The following can be used for joists:

• bars hewn from logs with minimum diameter 160 mm;
• logs with a diameter of 150 mm, which are simply trimmed;
• A board for floor joists can also be used if several such boards are stacked in a stack 200 mm high, pulled together and placed at the ends;
• rectangular wooden beam, the cross-section of which satisfies the design loads on the floor;
• The most convenient to use are ready-made adjustable logs.

Choosing wood for logs:

• Since when choosing which timber to use for floor joists, the quality of the wood plays a lesser role, most often preference is given to the cheapest pine or spruce. However, the use of these materials requires the preparation of appropriate floor waterproofing.
• Excellent durability and others performance characteristics have lags from larches for floors that are not afraid of exposure to water, but they immediately lead to a significant increase in the cost of this engineering solution.
• It is also moisture resistant aspen, which is why it is more expensive than spruce and pine.

In any case, when thinking about which wood is best to choose logs from, you should not spend extra money on lumber from the first and premium, since the second one will be quite enough. But at the same time, you should not go down to the third grade, which has a large number of knots, because the logs remain load-bearing elements, and if for them appearance does not matter, the strength should still remain high.

Therefore, one should not allow the presence of cracks, blue or rotten areas - such materials will not last the required time.

Also, great attention should be paid to the geometry of the beam so that it is not bent, twisted or otherwise deformed, since products made from it will be extremely difficult to level, especially if the log length is significant.

It is best if you can buy dried special technology lumber, after which they will have a residual moisture content of only 12%. But such material and at home, before it is installed, must be stored in dry conditions.

You should not use timber for floor joists with a residual moisture content above 15-18%, since after final drying they can lead, and this threatens general deformation of the entire floor structure, the appearance of unstable zones on it and the occurrence of an unpleasant creaking sound.

If the beam needs to be laid on a reinforced concrete base, then foamed polyethylene must be placed under it. If the logs rest on support pillars made of brick, then polyethylene should be laid between them, as well as between the soil and the pillar. In addition to polyethylene, you can waterproof wood from brick using roofing felt.

Impregnation for wooden floor joists

If lumber is used, it is strongly recommended that the floor joists be impregnated with various antiseptic compounds and fire retardants, which protects structural elements from being eaten by grinders and rodents, fungus and mold, and also for purposes fire safety. Many such compositions have been invented, some even have a double effect. They not only give the wood antiseptic properties, killing various biological living creatures, but also significantly increase its resistance to fire, since they contain fire retardants.

The composition must be diluted to the required concentration, although more often they are sold ready-to-use. The impregnation can be applied either by brush or by spraying it in the form of an aerosol, and small elements, such as underlays under floor joists, can simply be dipped into this solution. Antiseptic treatment requires spending approximately 100 ml of solution per square meter surfaces.

It is better to carry out this treatment twice - let the first layer absorb and dry, which will take about an hour at above-zero temperatures, and then repeat the treatment.

Before processing, beams must be thoroughly cleaned of dirt, traces of paint, lime, etc. There is no point in processing wet wood for the following reasons:

• the composition is much less absorbed into wet wood;
• After impregnation, the drying process of the material slows down significantly.

That is, wood with a humidity higher than 25% cannot be processed, although this humidity will no longer allow you to obtain an ideal result.

Section and dimensions of the logs

The reliability of the structure will depend not only on the choice of material, but also on how to choose floor joists, calculating them correctly. Even before purchasing a timber, you need to calculate its length and cross-section:

• The length of the floor joists must correspond to the dimensions of the room in which the floor will be installed, but at the same time be 20-30 mm less in order to prevent deformation from temperature changes.
• Beams are used for joists rectangular section with an aspect ratio of 1.5 x 2. If the floor rests on wooden floor beams, then the cross-section of the joist will depend on the length of the span between adjacent elements on which the joist will rest.

When insulating the floor

In case of floor insulation thermal insulation material must be left between the insulation and the finishing coating ventilation gap, having a thickness of at least 2 cm, and even better - 3-4 cm. Therefore, in this case, the timber must be taken taking into account this additive for the ventilation gap.

When installing joists on the ground

And if the logs rest directly on the ground, then you will need to additionally take into account the thickness of the knurling, which is laid on the cranial bars attached to the logs. It is best to buy timber whose cross-section has some margin.

If the floor is laid over an earthen base, then you can save on expensive large-section timber. It can be replaced with thinner timber, laid over shorter spans, and supported on brick pillars dug into the ground. The distance between the pillars should be 120 cm, and they themselves are made of red brick, since silicate brick can only be used in cases where the aquifer is deeper than two meters.

Of course, reinforced concrete or metal floor joists will have a smaller cross-section, because they are much stronger than wood and bend less.

Step between joists

The distance between adjacent lags depends on the thickness of the top flooring: the thicker it is, the larger the step between the supports can be, since a thick flooring will sag less under load. To know the exact ratio, you can use a special table, which states that:

• for boards 20 mm thick, the required support spacing is 30 cm;
• for boards 25 mm – 40 cm;
• for boards 30 mm - 50 cm, etc.

Instead of a table, you can use the rule - increasing the thickness of the timber by 5 mm allows you to increase the pitch by 100 mm.

Floor joists for plywood, which is more bending resistant, are calculated slightly differently. In this case, plywood with a thickness of 15-18 mm can rest on logs spaced 40 cm from each other. The plywood is attached to the logs in several places at once. The logs are laid so that the plywood sheets are fixed on them at the corners and in the center. That is, the edge of the sheet should be located in the middle of the beam.

Which lags do you prefer: wooden or metal? What kind of wood? Tell us about it in the comments - your experience is important to us.

Step V frame house is the selected (often identical) distance between identical frame elements. What is important is that the step is counted not from the edge of the boards, but from the center one to the center another board (see picture below).

Step in a frame house.

Let's go from floor to roof. First of all, the step between them is determined based on floor loads and from length span log(span is the length of that part of the joist that hangs in the air and is not supported by supports). It is convenient to calculate the dimensions and pitch of the lag using a special calculator. For first floor bedrooms the load is 300 kg/m2, for second floor bedrooms 200 kg/m2. You usually know the span length from your project. Substitute different sizes log and get optimal result(so that the safety margin is 1.5-2 times).

After receiving various options lag step, it makes sense to choose the lag step that suits us (choose your option):
1. Under plywood/OSB-3 2500×1250
There are 2 options:
Or a pitch of 417 mm (joining at every 6 joists).
Or pitch 627 mm (joining at every 4 joists)

2. Under plywood/OSB-3 2440×1220
There are also 2 options here:
Or a pitch of 407 mm (joining at every 6 joists).
Or pitch 612 mm (joining at every 4 joists)

3. Under insulation
If the insulation width is 600 mm, choose a pitch of 625-630 mm (can be combined with plywood 2500x1250).
If the insulation width is 500 mm, choose a pitch of 525 mm.
If the length of the insulation is 1200x600, you can cut it crosswise into 3 parts of 400x600 each and choose a pitch of 430-440mm (combining it with 2500x1250 plywood, trimming it a little), inserting the insulation between the joists along the resulting short side. Or choose a pitch of 417 mm (combining with plywood 2500x1250), but then you will have to trim each roll of insulation by 1 cm.

In my house I chose a pitch of 417 mm. Pictures from the project:

Step of jumpers between floor joists.
I wrote about jumpers. I install joists at 417mm intervals and headers at 1.25m intervals so that all plywood/OSB-3 joints (measuring 2.5m by 1.25m) meet on both the joists and headers.

Exceptions are made only for special cases:
- if you have parquet with a thickness of at least 8 mm with its joints offset relative to the plywood joints.
- if you do concrete screed thicker than 4 mm.
- if it is laid on plywood batten, thickness of at least 20 mm.
- if the plywood is tongue-and-groove

Personally, I made a plywood floor for myself, a concrete screed, and insulated my house with ecowool. You can read more in my other posts.

If the project is yours frame house If done by a professional, he will calculate the required lag step in advance.

I advise you not to skimp on the project, and certainly not to try to build without a project - it is very difficult, time-consuming and, moreover, leads to a large amount of unnecessary wood and other materials lying around in the shed for years until the next hypothetical construction or repair.

Here is a small, but hopefully useful post. Now you know what the correct pitch of the lag will be in your home.
And if you don’t want to think about it, then you can contact me to select a team in your region. Click on the box on the right of the red screen and I will help you find a team. Or just write to me by email, you will find contacts on the website.