Plywood or OSB (OSB): what to choose? Characteristics of plywood Elite grade E

05.05.2018

For quality arrangement In 80% of cases, logs are used for subfloors. With the help of beams you can not only make a strong wooden sheathing, but also level the rough base. What should be the height and width of the wooden beams? The article will examine the relationship between the main parameters of the lag, as well as the ability to withstand static loads on the floor.

Basic requirements for floors

The construction of logs for arranging a subfloor must have very high strength. Only in this case does it not deform under the influence of static and dynamic loads created by the finishing coating (laminate, ceramic tiles, solid boards, parquet), furniture, equipment and people. The size of the floor beams is determined by the intensity of the load per m 2 of floor, which is created during its operation.

The calculation is performed in accordance with the following defining parameters:

  1. When settling in wooden frame for attic floors, the floor must withstand a weight of 105 kg/m2;
  2. When finishing rough foundations on interfloor and basement floors, wooden floors should not deform even with a load of 210 kg/m2.

Based on the nuances described above, a calculation is made, according to which the main dimensions of the lags are accurately determined:

  • section;
  • length;
  • thickness;
  • width.

It is very important that the necessary parameters are observed, otherwise, due to the large static load, the wooden sheathing and floor board will begin to sag. This is fraught with complete destruction of both the rough and final coating.

Features of the materials used

Purely theoretically, logs can be made from almost any material:

  • metal;
  • plastic;
  • tree;
  • compound.

But the rather high price of most of the above building materials makes them uncompetitive in comparison with wood. That is why, as a rule, a thick board or timber is used to assemble a wooden frame. But this material also has one significant drawback - hygroscopicity.

Therefore, when choosing beams for flooring, it is advisable to choose only the type of wood that is less susceptible to rotting and deformation. Which wood should you choose? Larch would be the best option, but it is quite expensive. A more affordable alternative would be pine or spruce. At the same time, resin pockets and minor defects on the timber do not in any way affect its technical performance.

But do not forget that the material must be durable and resistant to deformation. Based on this, it follows that you cannot save on the strength of the lags. The moisture content of the wood should not exceed 20%, otherwise, during the drying of the wooden frame, the logs will bend, which will affect the horizontalness of the laid finishing coating.

Lag section

Calculation of the optimal cross-section (thickness) of the joists for the subfloor is carried out taking into account the following parameters:

  • The width of the span between adjacent support points.

    • Important! To assemble a wooden frame, logs with rectangular cross-section. In this case, the larger side of the beam should be located vertically. Thus, the floors acquire greater rigidity, which reduces the possibility of deformation to a minimum.

    To understand what the cross-section of a beam should be for different spans, consider the typical dimensions of beams for flooring in residential premises:

    In other words, the calculation of the optimal section is determined by the following expression: the height of the beam should exceed the width by approximately 1.5 times. However, there are some nuances here that are worth knowing about. The greater thickness of the board inevitably affects its price. To reduce the cost of purchasing logs with a large cross-section, in the process of arranging a wooden frame under the beams, you can make supports from concrete or bricks. If the supports are placed at intervals of approximately 1 m, the thickness of the beam can be reduced by half.

    In some cases, the thickness of the joists is determined by the type of material from which they are made. Very often, when arranging the floor of the second floor of a high-rise building, beams are used as reinforced concrete floors. Optimal thickness metal elements determined by its bending strength.

    Linear dimensions of beams

    Length and width are the main parameters that must be taken into account when choosing beams for arranging a wooden frame. How to make a competent parametric calculation?

    1. Definition of width. As already noted, logs with a rectangular cross-section are chosen for the subfloor. During installation, they are laid on edge to give the structure greater rigidity. In this case, the formal width of the beam should be 2 times less than the height;
    2. Determination of length. The length depends on the area of ​​the base itself. However, it is advisable to select the size of the logs taking into account the technological gaps - the distance from the beam to the wall should be approximately 3 cm. The gaps are made in order to avoid significant deformations of the wooden frame during thermal expansion of the material.

    Determining the step size for laying joists

    Calculating the optimal pitch for wooden beams is quite difficult to determine. If there is a directly proportional relationship between the cross-section of the beam and the size of the span, then with the interval of laying beams the situation is different. A simplified version of the calculation should be as follows: the larger the step between the logs, the thicker the board that is laid on the wooden sheathing. Why is this so?

    The explanation of this rule is not difficult to understand: the thicker the board, the less it will be subject to deformation. However, it should be taken into account that the interval between the layout of the beams does not depend in any way on the material from which they are made. Indeed, in this case we are talking about the ability of the board to withstand static and dynamic loads.

    One of important issues In the construction of a house is laying the floor. Current trends in interior design bring us back to using natural materials. Wood is the most environmentally friendly and practical of them. This coating adds not only comfort and aesthetics. It is durable, highly durable, and retains heat well.

    This floor is ideal for both a summer house and country house, and for a city apartment. Renew paint or varnish coating maybe once every 4-5 years. The tree will serve you for many decades. However, it is necessary to seriously approach the issue of preparing the base for its installation. Among the many methods, laying on logs is considered the most proven.

    What are lags for?

    Floor joists are floors made of wood, metal, plastic or reinforced concrete. As a rule, they have the form of beams that are laid across the future finishing surface. This is a kind of lathing that serves as the base of the floor.

    Most often they are made of wood in the form of bars of certain parameters. It is more accessible, cheaper and is not inferior in quality to other materials. This method of installation is used to securely secure the floor to avoid sagging under heavy furniture, so that it does not vibrate or creak. According to statistics, it is used in 90% of cases.

    The main advantages of the log:

    • noise absorption;
    • floor ventilation;
    • increase in thermal conductivity;
    • the ability to use empty space for various utilities;
    • floor leveling;
    • increasing the strength of the coating to several tons per square meter;
    • ease of installation and replacement;
    • low cost.


    The material for logs is most often pine, spruce or fir. Larch is more expensive, so it is not so popular. Since they serve as a base for the floorboard, grades 2 or 3 are quite suitable. They may not be as neat as grade 1. The presence of knots and smudges of resin will not affect the reliability of the structure.

    As a rule, wood is stored under certain conditions. The humidity of the material ready for use should be about 15-20%, but no more. Before starting work, the wood must be treated with special impregnations.

    They are harmless to human health and often require simple dilution with water in certain proportions. This prevents the appearance of fungus and mold on the tree, protects against bugs and rodents. The procedure is quite simple, but requires reapplication after 3 or 5 hours.

    Floor joists do a lot useful functions. It is worth keeping in mind that incorrect installation can lead to dire consequences in the future. The shape of the beam must be rectangular.

    They best withstand heavy loads in a ratio where the height is one and a half or two times greater than the width. The beam is always placed only on the edge. The table shows the size of the lag section for certain spans. The step between them in this case is 70 cm:

    The size of the section depends on the strength of the material used and the expected load on the floor. For residential premises it is established that it does not exceed 300 kg per m2. These values ​​are recognized by experts. However, they can be made thicker depending on the situation. For example, it is necessary to increase the space for thick insulation. Or an increased load on the coating is expected. How stronger material, the smaller its size can be. This applies, for example, to iron.

    The length of the logs must correspond to the length (width) of the room minus 2.5-3 cm. This margin is necessary to maintain the strength of the structure in case of fluctuations in temperature and humidity. It is recommended to use long logs. It’s good if their size matches the length of the room.

    If it is necessary to join them, then the joints should be shifted relative to the neighboring ones by about half a meter, or better yet, by a meter. A support is made at the splice site. It is usually done in column form. Splicing occurs using galvanized plates, but more often - half-tree.

    Be sure to take into account the distance between the floor joists. Professionals call it a “step.” It is determined depending on the parameters of the floorboards. The thicker the floor covering, the larger the pitch can be. Accordingly, the thinner it is, the smaller the step we take.

    A pattern can be deduced from the table. If the thickness of the board increases by 0.5 cm, then the step increases by 10 cm. For a more durable coating (for example, plywood and OSB), calculations may be different.

    Since these materials are more resistant to deflection, the pitch increases. With a thickness of 18 mm, the pitch will be up to 40 cm. With 25 mm, it will be up to 60 cm. We attach each sheet to three different lags. Be sure to fasten the center and edges, going halfway up the joist.

    The logs are laid on wood, soil and concrete. First you need to know what tools are required for this. So, in addition to the bars themselves, you must have a level, a jigsaw or hand saw. We stock up on screws, screws, anchors and nails. Be sure to have a hammer drill with you (when laying on concrete), usually an axe, a screwdriver or drill, a hammer and a nail puller.

    If the joist is attached to wooden floors it is necessary to fasten them to the sides of the beams. This is done based on the fact that beams are usually not level. In addition, this method helps not to raise the floor, saving precious centimeters in rooms with low ceilings.


    If the height allows, then, as an option, the timber is laid on top across the beams. We secure them with 6 mm screws, having previously drilled a hole 2.5 mm smaller in diameter. This will prevent the wood from splitting. The length of the screw should be 2.5 times longer than the width of the joist.

    When laying logs on the ground, it is necessary to clean and compact it in advance. Next, measurements are taken to install the pillars. They will serve as a support. The distance from the wall to the first log should be from three to twenty centimeters. Holes 10 cm deep are dug along the intended distance, filled with sand and filled with water for greater strength. This will be the foundation for the pillars.

    It is recommended to make its size at least 40 by 40 cm. Then polyethylene is laid, and a column of two or three bricks secured with cement is erected on top of it. Then they are covered with roofing felt, and timber is laid on top. The logs are attached with galvanized corners to the walls or to the crown of the log house.

    Joists are often laid on a concrete base. Waterproofing in this case is extremely necessary, otherwise the floor will constantly become damp. Regular plastic film is quite suitable here. However, experts are increasingly beginning to use foil insulation - this is foamed polyethylene with a layer of foil, which is laid towards the living space, reducing heat loss.

    The beam is attached to the concrete using anchors. Insulation is laid between the joists, but not under them. Concrete screed, as a rule, eliminates the hassle of leveling joists before laying floorboards.

    Make sure the wood is dried and treated with antiseptic or bitumen. This will significantly extend the service life of the structure. When the humidity is more than 20%, the tree can become warped, compromising the integrity of the structure. Boards brought from the warehouse must lie in room temperature several days. This is especially true during the winter season. It is not recommended to lay the floor when the air humidity is less than 60%.

    You should not saw or plan boards in the room where the floor is being installed. Sawdust can cause rot.

    Don't forget to use waterproofing. For sound insulation, as a rule, fiberboard, rubber, polyethylene foam, slag or sand are used. The heat in the house will remain longer if you fill the voids under the floor with mineral wool, expanded clay, expanded polystyrene or isospan.


    Use the rule after installation. Lay it across the beams, remove gaps, leveling the height. This is easy to do with the help of special modern adjustable fasteners that appeared on construction market. The floor is laid only after all leveling procedures.

    The smaller the pitch, the longer the floor will last. However, the main indicator of durability is the material of the coating and base. The most durable wood is larch.

    The installation of beams is usually carried out along the window, i.e. across the room. The floor boards are then placed along the length of the room, i.e. from the window. However, this is just a recommendation and a matter of taste.

    The floor is laid from the corner, placing the boards perpendicular to the joists. The distance from the walls should be about 1 cm. This is left in case the wood deforms depending on temperature and humidity environment. This distance is covered by the baseboard. If the boards lie close to the wall, the floor may swell.


    A board is attached to each beam. Holes for screws should be drilled in advance to avoid delamination.

    The most common option for the space between the joists is from 50 to 56 cm. As a rule, it does not exceed a distance of 69 cm.

    Removing joists and wooden floors is quite simple. It is necessary to remove all the furniture from the room, remove the baseboards, and open the boards or sheets of chipboard. After inspection, the old boards are replaced with new ones. The logs themselves can be partially replaced. Simply cut out a piece of rotten wood and install a new one.

    Don't forget to use a protective impregnation on new boards. Check the ends of the beams for rot, and inspect the base insulation, if any. Repairing the floor can be a reason to insulate your home.

    Joists are deservedly the simplest and most popular way to create a reliable foundation for our floor. If desired, anyone can take up this interesting business and step to achieve your goal step by step. The most pleasant reward for your hard work will be a warm and cozy atmosphere for many years to come.

    When building a house, a private developer rarely has to choose the type of flooring. From reinforced concrete products, metal or plastic I-beams and wooden joists, the choice, as a rule, remains with the latter. But the developer will be faced with questions: what timber to use for the floor joists, how to choose the right type of wood, cross-section and how to calculate the optimal amount of material.

    Why are there lags?

    Laying floor joists
    Of course, affordability is an important argument when choosing joists for flooring or between floors, but not the only one and not the most important one. Using this option allows, in case of independent work, to perform all operations manually, without the use of special equipment. Even though this method of flooring is inferior in durability to many other options, it has undeniable functional advantages, some of which are determined by the properties of wood, and others by design features. Among these advantages are the following:

    • ensuring uniform load distribution from the house to the foundation, despite the fact that there is no significant increase in the weight of the entire building;
    • the ability to install a reliable thermal insulation layer, for which you can use a wide range of insulation materials: starting from expanded clay and sawdust and ending with products from mineral wool or expanded polystyrene;
    • routing optimization utility networks for home life support, which can be neatly placed in the underground space;
    • possibility of adjusting the floor level;
    • quick installation, which is not particularly difficult even for a novice builder and can be completed in a very short time.

    Of course, this is not the entire list of advantages of this type of overlap. It should also be noted that a properly installed floor on joists does not require special leveling and the process of installing a rough foundation, and therefore installation flooring doesn't present any difficulty.

    Logs: basic material requirements

    In principle, logs, which are wooden beams, can be laid on any base, including directly on the ground. The cross-sectional dimensions of the logs may vary, but, as a rule, the aspect ratio should be from 1:1.5 to 1:2. What cross-section to choose logs with is determined design features ceiling, as well as load: load-bearing and dynamic.

    For work, it is most convenient to purchase finished goods, but it is quite possible to make them yourself using suitable wood. There are no special requirements for it, except that it must be natural humidity, ideally - 18-20%. The most popular type of wood for their manufacture is pine., although spruce and fir are also successful. Larch is used less often, due to its more high price. But in case there is a problem high humidity or high level groundwater- this is the most optimal choice, but not without alternative: logs made of aspen can cope with this task perfectly. There are no high requirements for the quality of the wood itself, and for the manufacture of logs, material of the 2nd or even 3rd grade is mainly used.

    Floor joists made of pine

    In private housing construction (during the construction country house, for example), sometimes logs are even made from ordinary boards, having previously fastened them with self-tapping screws and with the obligatory subsequent installation of them “on edge”. In some cases, you may encounter the problem that the standard length is not enough for the overlap device. Then the method of merging two elements together is used. The most reliable option is a half-tree joining, forming something like lock connection, but let’s say “butt” - alternative way docking. In this case, it is necessary to install a support (a brick column, for example) or a column (if we are talking about an interfloor ceiling) in front of the logs.

    How to correctly calculate the cross section of the lag

    In order to determine which section of timber is suitable for the installation of floor joists, the following data must be taken into account:

    • maximum operating load value. For example, when building a residential building, you need to focus on the value of 300 kg/m2;
    • span length between supports, which can serve as cross beams, timber frame, support posts or other structural elements, on which the logs will rest with their ends;
    • material thickness used for finishing flooring;
    • required clearance for device natural ventilation, which is usually from 2 to 5 cm.

    Considering the fact that logs are essentially beams that work in bending, they are installed with support on a narrower edge. Due to this it is ensured maximum rigidity even with a small section of timber. For example, for 3-meter spans a beam with a section of 80x150 mm or 100x180 mm is suitable, for 4-5 meter spans - 100x180 mm and 150x200 mm, and for 6-meter spans you will need material with dimensions of 180x220 mm.

    Floor joists fastened together

    Sometimes it is permissible to install floor joists in a house made of timber with a cross-section smaller than necessary. In this case, you can save on the wood itself, but you will have to spend money on purchasing red brick and installing special supports for the logs. As a rule, such “savings” are fully justified in the case of erecting a floor covering in conditions higher level groundwater, that is, when laying it on the ground is out of the question. Posts will not only help protect the tree from negative impact humid environment, but at the same time they will also reduce the load on the beam due to the reduction in span. In this case, you can use timber with a smaller cross-section.

    In order to correctly calculate the cross-section of the material, you should contact specialists who, based on the data provided on the expected loads, as well as the type of wood and its moisture content, will produce necessary calculations for optimal results. As a last resort, you can use online calculators located on specialized websites.

    Pitch and amount of material

    The logs are laid parallel to each other with a certain pitch (distance) between them. This value depends on:

    • planned load;
    • lag beam sections;
    • type and thickness of flooring material: if thin sheet material, then the step must be reduced, and if boards 30 mm thick are used, then, on the contrary, it can be increased.

    In turn, the number of logs and, accordingly, the amount of material for their manufacture will depend on the step size. Therefore, when calculating the step, you should start from the length or width of the room, depending on the direction in which the logs will be laid. Next, the cross-section of the timber that will be used for this is taken into account, and it is also taken into account that the outermost logs are installed at a distance of 20-30 cm from the wall. That is, it is necessary to solve the usual arithmetic equation:

    the pitch is equal to the length of the room divided by the sum of the width of the beam and the distance from the walls

    Accordingly, to find out the number of required units of material for this you need to:

    Divide the length of the room by the sum of the width of all the joists, the step size and the distance from the walls.

    Features of the device for overlapping joists

    As a rule, the timber used for making logs does not have any special treatment and therefore must be protected. In addition to the necessary waterproofing work, treatment with antiseptics and fire retardants should be carried out.

    Before you begin installing the logs, you should decide in what way and with what fastening elements this work will be performed. Traditionally, for a long time there was no alternative to nails, but the use of a system using metal corners with zinc coating for corrosion protection. Self-tapping screws are used to secure them. In the case of installing the ceiling along joists on a concrete base or grillage, dowels should be used, but first perform waterproofing, for which various mastics or roofing felt are successfully used.

    Attaching joists to a concrete base

    When installing joists, the direction of their laying is always taken into account. This is especially important when installing floorboards, since they must be located along the line sunbeam. Therefore, the logs must be installed perpendicular to it. But in hallways, kitchens, terraces, that is, in those rooms where traffic in the house is the most intense, aesthetics can sometimes be sacrificed for the sake of practicality and reliability. In this case, the logs should be located perpendicular to the direction of movement.

    One of the most difficult and important points when laying the lag is horizontal leveling process. Special lifting and adjustment devices, initially tested on plastic joists, come to the rescue. The mechanism itself is quite simple and consists of plates with a rod equipped with a threaded nut-bolt connection, with the help of which the log height is adjusted. Such a system also turns out to be very useful during operation, for example, during shrinkage manifestations, which are indicated by the “musicality” of the floor in the form of a creaking sound.

    And finally, when starting to install floor joists, you should know that despite the rather simple and uncomplicated installation system, this process is quite labor-intensive and responsible. In addition, the amount of work can vary greatly depending on what will act as a support or base for the logs. The most difficult option is to install the logs on the ground, and the most simple types can be considered work on a concrete base or work related to the installation of interfloor ceilings.

    Floor beams or ceiling joists are the supporting structure of the house, therefore, before you begin to independently install floor joists in a log house or bathhouse, we strongly recommend that you take special care approach the choice of material And calculate correctly floor construction.

    For the manufacture of floor joists, it is best to use dry, first-grade material impregnated with a fire-bioprotective composition.

    Beams are most often embedded:


    How to ensure the strength of floors and convenient installation

    Having previously marked the places where the beams will be inserted, cuts are made in the log and tight beams are inserted into them at a distance of about 600 mm from each other. This distance between the beams provides the necessary strength of the floors. Most types of insulation are produced with a width of exactly 600 mm, which ensures convenient installation of heat and noise insulation. With this method of installing logs, there is no need to attach them additionally to the wall.

    Floor joists can also be mounted after the frame has been assembled, securing them to the wall using special brackets and screws. The construction market now hasa huge variety of fastening devices. But more correct and reliable installation method - first!

    Issues arising during the construction process

    During construction log house, log bathhouse Questions naturally arise: What section should I embed the floor beams (floor, ceiling)? What load can they withstand? wooden joists(beams)? Which maximum length beams is possible for what section of board, beam, log?

    Based on the table below, it is easy to calculate the cross-section of the log, depending on its length. The data is given for standard spans with a width of 2 to 6 meters, with a frequency of lags every 600 mm (distance between lags 600 mm) Design load 300 kg per 1 sq. meter. The table shows the breaking loads for these logs in kg per square meter.

    Simply put, the numbers on a colored background are the load in kilograms per 1 m2, at which the ceiling will simply break. But in order to prevent the floor from “springing”, there is also an indicator of the bending of the beam. Blue background - the floor will not “spring”, yellow - the maximum permissible, and red background the floor will sag under a load of 300 kg more than the permissible norm.

    Table for calculating the destructive load (kg/m2) on the joists (beams) of the floors of a log house.

    log length m 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0
    log section mm
    Board 100x50 733 587 489 419 367 326 293 267 244
    Board 150x50 1650 1320 1100 943 825 733 660 600 500
    Board 200x50 2933 2347 1956 1676 1467 1304 1173 1067 978
    Beam 200x100 5867 4693 3911 3352 2933 2607 2347 2133 1956
    Beam 200x200 11733 9387 7822 6705 5867 5215 4693 4267 3911
    Log 200 6912 5529 4608 3949 3456 3072 2765 2513 2304
    Log 220 9199 7359 6133 5257 4600 4089 3680 3345 3066

    Blue are highlighted in the table values ​​with safety margin

    Yellow the values ​​are highlighted in the table maximum permissible by beam deflection for these conditions

    In red values ​​are highlighted unacceptable for deflection(more than twice the permissible norm) of beams for these conditions.

    Note: additional rigidity can also be given to the beam by splicing two or more boards in thickness.

    Logs are lathing elements for flooring. They are necessary for the final floor structure to be of high quality: smooth and strong. Strengthening and leveling the floor surface without joists is very problematic. An unreinforced covering will sag under the influence of heavy furniture, and the floor itself will creak and vibrate when walked on it. Floor joists are almost always installed. How is their size selected and installation done?

    Why is laying joists so important?

    The main function of the log is to create a flat surface for the following work. But sheathing under the deck also serves other purposes. They promote complete ventilation of the underside of the flooring, which prevents the boards from rotting.

    .

    This timber base feature has great value in those rooms where the floor is laid on the ground and dampness due to groundwater creates serious problems even with a high subfloor.

    With the help of joists, a space is formed between the flooring itself and the base of the floor - a kind of buffer that helps improve the soundproofing qualities of the floor. The same space is used for laying a layer of insulation, and, if necessary, utilities.

    Installing floor joists allows you to obtain a durable floor even with an uneven base due to support points placed at a certain pitch.

    Lathing materials

    As a base for the flooring, you can use any materials that meet the requirements of strength, evenness and low deformation coefficient under load. These technical characteristics correspond to products made of metal, plastic, reinforced concrete, wood and compounds produced on the basis of synthetic resins. What kind of joists are best to use for the floor? Comparing the cost of all the above materials allows us to identify the favorite - wood. In practice, ordinary wooden beams are used for logs.

    The material for timber is usually coniferous wood. The timber used for floor joists is made from spruce, pine, and fir. But larch is recognized as the best option, since its wood is not only highly durable, but also resistant to rotting.

    Spruce and pine are more popular only due to their low cost.

    When choosing a material, you can ignore the presence of resin pockets and other minor defects and buy grade 2 or 3 lumber - the functionality of the timber base will not suffer from this.

    Beam made from Siberian larch.

    When choosing logs, you can save on material by replacing larch with spruce, but saving on the moisture content of the beams is not recommended in any case. The moisture content of the timber should not be more than 20%; at higher humidity values, the material will be deformed during the drying process, which will lead to problems with the finished floor.

    If you have chosen spruce or pine as the material for the sheathing, then you should take care of waterproofing the beams when laying them. The logs can be laid on different floors, depending on the characteristics of the base they will differ and waterproofing works. If the bars are mounted on reinforced concrete slabs floors, you first need to lay a layer of foamed polyethylene. In the case when the logs are attached to brick columns, polyethylene is laid between the soil and the column itself, as well as between the column and the beam. For the layer between brick and wood, roofing felt is suitable instead of polyethylene.

    Foamed polypropylene.

    Floor joists, regardless of the type of wood, are recommended to be treated with an antiseptic before installation. Such precautions are most relevant in wooden private houses, where woodworms can become a big problem for the owner of the house, as they pose a threat to the durability of the entire structure.

    Determining the dimensions

    The reliability of the entire floor structure depends on how correctly the size of the joist is selected. Before purchasing beams, you should calculate their required length and thickness.

    There are usually no problems with the length of the lag: depending on the direction of installation, it should be equal to the length or width of the room where the floor is being made. The best option is the length of the timber 2.5-3 cm less than this distance. This ratio of two values, when the length of the log is slightly less than the length of the room, allows you to avoid deformation of the structure due to temperature changes.

    The length of the beam should be 2-3 cm shorter than the width of the room.

    It is advisable to make floor joists from whole lumber, but this is only possible when the size of the timber matches the parameters of the room. If the length of the bar is not enough, then splicing two elements is used. The work is carried out in half a tree, sometimes using galvanized overlays.

    It is not difficult to splice two bars, but in order for the structure to be strong, two rules must be strictly followed:

    • There must be some kind of support under the splice area, the best option there will be a support column;
    • If two adjacent logs are spliced, then their splice points should be offset relative to each other.

    Failure to comply with these requirements entails the risk of low floor rigidity at the junction of the timber.

    Methods for splicing lags.

    Adjacent floor joists should be spliced ​​with an offset of one meter. This parameter affects the size of the original bars, which should also be taken into account when purchasing them.

    If everything is quite simple with the length of the beam, then determining the parameters of the lag section is more difficult. What is it? The cross-section of the log is its thickness, which depends both on the material of the beam and on the design characteristics of the future floor.

    The cross-section of the joists for the flooring is calculated based on the maximum possible load on the floor and the size of the spans between the support points of the beams. The generally accepted maximum load value is 300 kg/m2 - this parameter is applicable to residential premises.

    When determining the size of the joists based on this load level, the length of the span between adjacent beams is taken into account. How are the distance between floor joists and their thickness related? For this purpose, there is a special table of sizes used by specialists. In the most common cases, the correspondence looks like this: with a span length of 2 m, a beam of 110x60 mm is used, with a span length of 3 m - 150x80 mm, with a span length of 4 m - 180x100 mm. The larger the span, the thicker the timber from which the logs are made should be.

    The cross-section of the timber is usually rectangular. In order for the logs to withstand pressure, the rectangular beam is laid “on edge”. This feature of installing the base for the future floor ensures the maximum level of timber rigidity with a minimum volume of lumber.

    The thickness of the joists used for flooring may be greater than the specified parameters. Installing logs from timber of greater thickness is not prohibited, and sometimes it is simply necessary.

    Sometimes increasing the cross-sectional dimensions of the timber is necessary to lay a thick layer of insulation.

    When choosing joists for a new floor, you should also take into account that if you are going to install the floor in non-residential premises, then the load on the structure can exceed 300 kg/m2. This parameter will have to be calculated by calculation, and then, based on the data obtained, logs with suitable section parameters will have to be selected.

    The size of a metal beam may be smaller than a wooden one.

    If instead wooden beam If you decide to use beams made of metal or reinforced concrete, their thickness may be less. This is explained by the fact that they have a higher resistance to deflection compared to wood.

    How to determine the step?

    The size of the joists is determined by the size of the span between them, which in turn depends on the thickness of the board used to lay the wooden floor. Here you should be guided the following rule: The thicker the flooring, the larger the step you can take. There is a completely logical explanation for this, because the thicker the board, the less susceptible it is to sagging under the influence of gravity.

    The ratios are as follows: with a board thickness of 2 cm, you can take steps up to 30 cm, with a thickness of 2.5 cm - up to 40 cm, with a thickness of 3 cm - up to 50 cm. In order to calculate the possible span length with a larger board thickness, you can use the formula: increasing the thickness of the flooring board by 0.5 cm increases the possible length of the joist step by 10 cm.

    If plywood or OSB is used instead of flooring boards, then the calculations are slightly modified. These materials are more rigid in bending, so their thickness is smaller. With a material thickness of 1.5-1.8 cm, you can plan a lag pitch within 40 cm, with a thickness of 2.2-2.4 cm - within 60 cm.

    When using plywood or OSB, sheets of material must be attached to the joists in three places. Floor joists should be positioned so that the fastenings are at the edges of the sheet and in the middle. In this case, the edge of the sheet is not laid across the entire width of the beam, but only up to half.

    Laying joists on the base

    Wooden logs can be attached to any base, the main thing is to follow the installation rules. To carry out the work of laying sheathing from logs, you will need the beams themselves, a jigsaw, a level, a screwdriver and fasteners. A jigsaw can be replaced with a hand saw.

    Attaching the joists to concrete floor implies the use various designs, which are divided into simple and adjustable. Adjustable elements have screws in their design, with which you can align the logs.

    Special anchors or screws are usually used as fastening. Theoretically, it is possible not to secure the joist bars at all, but then there is a risk of destruction of the floor structure due to the joist moving to the side.

    In addition to the tools listed, additional devices may be required. Do-it-yourself installation of floor joists on concrete or soil requires additional fixation using a hand hammer drill.

    Adjustable logs.

    Laying the logs on the ground is done as follows. First, the support pillars are installed. To do this, dig holes about 10 cm deep, fill them with sand and spill them with water for good shrinkage. A plastic film is laid on the sand, on top of which a brick column is erected on the mortar. Its length and width are usually equal to the edge of the brick. The finished columns are covered with roofing felt. Timber is laid on them without fixation, then the logs are hemmed to the walls with galvanized corners.


    How to lay logs for the future floor, if the basis is wooden beams? The order of work depends on how the timber is laid on the beams: across them or along them. If the beam is placed across the beams, then the logs are attached to the beams with ordinary self-tapping screws of suitable length.

    In this case, it is important not only to treat the logs with an antiseptic, but also to drill holes, otherwise the risk of the beam splitting will be very high.

    If you decide to attach the beams along the beams, then to compensate for the difference in their height, the logs can be attached not only on top, but also hemmed on the sides. Having completed all the work correctly, you will be able to level the floor with the least loss of room height.

    Attaching the joists to the concrete floor is done as follows. If you are carrying out floor installation work on the ground floor of a building, then the ceiling should be waterproofed with polyethylene film. You can use foamed polyethylene with a foil layer. This material will not only waterproof the wood, but also reduce heat loss during further use of the room.

    The timber is laid out in accordance with the previously determined lag pitch and set to the level. To level the base for flooring, pads made of plywood and the bars themselves are used. After this, the logs are fixed to the floor. The best option is the use of anchors mounted under a screwdriver. There is an alternative way of laying timber on a concrete floor using stands. The stands are attached to the floor slab, and the logs themselves are attached to them with self-tapping screws.

    When preparing to install the floor, it is important to correctly calculate the length and cross-section of the joists, and also think about what distance will need to be laid between the floor joists. If all the parameters are determined correctly, then by using high-quality timber and responsibly carrying out all the work on its installation, your floor will be smooth and beautiful, and will not sag under the weight of furniture or creak when walking.

    Plywood is considered popular for a reason building material. It has aesthetic characteristics, and after processing it becomes durable, elastic and resistant to moisture. This makes it possible to significantly expand the scope of its application. When it comes to the ability of this material to resist deformation, then in this case the quality of the product is determined by two main criteria - the tensile strength of plywood, as well as the bending strength of plywood.

    Of course, determining the strength characteristics of plywood sheets is a whole process in which it is worth considering many nuances. This takes into account the type of wood, the condition of the raw materials, moisture content, processing technology and other criteria:

    • impact strength - the ability to absorb work upon impact without any destruction;
    • wear resistance - the degree of destruction of a material upon regular exposure to its surface. Experience has shown that wet wood wears out much faster than dry wood;
    • ability to hold metal fastenings- an important property. The fact is that installing a fastening element can trigger deformation processes. So, if the material is not strong enough, then when driving a nail or screwing in a self-tapping screw, there is a risk that the plywood sheet will crack;
    • deformability - the appearance of deformations is inevitable when exposed to loads.

    In general, plywood is a unique building material. Its secret lies in the technology of laying veneer. The latter is a thin layer of wood cut from a tree trunk. This is not the most durable raw material. To eliminate this drawback, it is laid so that the fibers are in mutually perpendicular directions. Usually the minimum number of such layers is 3, but maximum quantity in theory it can be unlimited, although in practice it is rarely more than 30.

    Strength of plywood of various grades and thicknesses

    However, the correct placement of fibers is not the most main secret the strength of this material. After all, plywood only partially consists of wood, and the rest is represented by an adhesive composition that is used to hold each layer together. Various substances are used for this:

    • urea-formaldehyde is a mixture of urea resins with a small amount of formaldehyde. Typically, this composition is used during the production of FC brand goods - an environmentally friendly and safe product. It has outstanding characteristics in terms of strength, but copes well with interior finishing work;
    • phenol-formaldehyde - the main danger here is a substance called phenol, which is toxic to humans. But it repels moisture well, so it is used for the production of FSF - a fairly durable and reliable building material;
    • Melamine formaldehyde is a safe substance used in the production of the FKM brand. The only drawback of the product is its high cost;
    • bakelite resins - make it possible to create high-strength products that no other wood can compare with. But if the level of flexibility is important to you, then through this processing it is actually completely lost.

    If you are interested in the strength of the material, then when studying the technical characteristics, pay attention to the density indicator. On average, this value ranges from 550-750 kg/m³. For comparison, the density of bakelite plywood is 1200 kg/m³.

    The thickness of the building material also matters. Of course, the strength of 10 mm plywood will be lower than that of sheets with a thickness of 12 mm. These features also need to be taken into account.

    How to calculate the strength of plywood yourself?

    It is necessary to take into account the strength of plywood when arranging the roof, construction load-bearing structure, during the manufacture of furniture (racks, cabinets, etc.) or laying flooring. This will help determine what load it can withstand and select suitable materials.

    Special online calculators will help you make the necessary calculations; you can also seek help from a specialist or calculate the strength of plywood yourself to make sure your choice is correct.

    To do this, use the formula for determining deflection plywood sheet, which looks like this:

    f = k1ql4/(Eh3), where:

    • k1 - calculated coefficient;
    • E - elastic modulus of wood;
    • h is the thickness of the plywood sheet;
    • l - length;
    • q is the value of the plane load.

    At first glance, the formula seems simple, but we advise you to be careful in your calculations and double-check the result obtained several times. You can find the calculation data on the Internet.

    So there is a cell with clear dimensions of 50x50 cm, which is planned to be covered with plywood with a thickness of h = 1 cm (actually, according to GOST 3916.1-96, the plywood thickness can be 0.9 cm, but to simplify further calculations we will assume that we have plywood with a thickness of 1 cm), a flat load of 300 kg/m2 (0.03 kg/cm2) will act on the plywood sheet. Ceramic tiles will be glued to the plywood, and therefore it is very desirable to know the deflection of the plywood sheet (calculation of plywood strength is not discussed in this article).

    Ratio h/l = 1/50, i.e. such a plate is thin. Since we technically cannot provide such fastening on supports so that the logs perceive the horizontal component of the support reaction that occurs in the membranes, then it makes no sense to consider a plywood sheet as a membrane, even if its deflection is quite large.

    As already noted, to determine the deflection of the plate, you can use the corresponding design coefficients. So for a square slab with hinged support along the contour, the calculated coefficient k 1 = 0.0443, and the formula for determining the deflection will have the following form

    f = k 1 ql 4 /(Eh 3)

    The formula does not seem to be complicated and we have almost all the data for the calculation, the only thing missing is the value of the elastic modulus of wood. But wood is an anisotropic material and the value of the elastic modulus for wood depends on the direction of action of normal stresses.

    Yes, if you believe regulatory documents, in particular SP 64.13330.2011, then the modulus of elasticity of wood along the fibers E = 100,000 kgf/cm 2, and across the fibers E 90 = 4000 kg/cm 2, i.e. 25 times less. However, for plywood, the values ​​of elastic moduli are taken not simply as for wood, but taking into account the direction of the fibers of the outer layers according to the following table:

    Table 475.1. Moduli of elasticity, shear and Poisson's ratios for plywood in the plane of the sheet

    It can be assumed that for further calculations it is enough to determine a certain average value of the elastic modulus of wood, especially since the plywood layers have a perpendicular orientation. However, such an assumption will not be correct.

    It is more correct to consider the ratio of elastic moduli as an aspect ratio, for example for birch plywood b/l = 90000/60000 = 1.5, then the calculated coefficient will be equal to k 1 = 0.0843, and the deflection will be:

    f = k 1 ql 4 /(Eh 3) = 0.0843 0.03 50 4 /(0.9 10 5 1 3) = 0.176 cm

    If we did not take into account the presence of support along the contour, but calculated the sheet as a simple beam with a width b = 50 cm, a length l = 50 cm and a height h = 1 cm under the action of a uniformly distributed load, then the deflection of such a beam would be (according to the calculated diagram 2.1 table 1):

    f = 5ql 4 /(384EI) = 5 0.03 50 50 4 /(384 0.9 10 5 4.167) = 0.326 cm

    where the moment of inertia I = bh 3 /12 = 50 1 3 /12 = 4.167 cm 4, 0.03 50 is the reduction of a plane load to a linear load acting across the entire width of the beam.

    Thus, supporting along the contour allows you to reduce the deflection by almost 2 times.

    For plates that have one or more rigid supports along the contour, the influence of additional supports creating the contour will be less.

    For example, if a sheet of plywood is laid on 2 adjacent cells, and we consider it as a two-span beam with equal spans and three hinged supports, not taking into account the support along the contour, then the maximum deflection of such a beam will be (according to design diagram 2.1 of Table 2):

    f = ql 4 /(185EI) = 0.03 50 50 4 /(185 0.9 10 5 4.167) = 0.135 cm

    Thus, laying plywood sheets over at least 2 spans allows you to reduce the maximum deflection by almost 2 times, even without increasing the thickness of the plywood and without taking into account the support along the contour.

    If we take into account the support along the contour, then we have, as it were, a plate with rigid pinching on one side and hinged support on the other three. In this case, the aspect ratio is l/b = 0.667 and then the calculated coefficient will be equal to k 1 = 0.046, and the maximum deflection will be:

    f = k 1 ql 4 /(Eh 3) = 0.046 0.03 50 4 /(0.9 10 5 1 3) = 0.096 cm

    As you can see, the difference is not as significant as with hinged support along the contour, but in any case, an almost twofold reduction in deflection in the presence of rigid pinching on one of the sides can be very useful.

    Well, now I would like to say a few words about why the elastic moduli for plywood differ depending on the direction of the fibers, because plywood is such a tricky material in which the directions of the fibers in adjacent layers are perpendicular.

    Determination of the modulus of elasticity of a plywood sheet. Theoretical background

    If we assume that the modulus of elasticity of each individual layer of plywood depends only on the direction of the fibers and corresponds to the modulus of elasticity of wood, i.e. impregnation, pressing during manufacturing and the presence of glue do not affect the value of the elastic modulus, then you must first determine the moments of inertia for each of the sections under consideration.

    Plywood with a thickness of 10 mm usually has 7 layers of veneer. Accordingly, each layer of veneer will have a thickness of approximately t = 1.43 mm. In general, the given sections relative to perpendicular axes will look something like this:

    Figure 475.1. The given sections are for a plywood sheet with a thickness of 10 mm.

    Then, taking the width b = 1 and b" = 1/24, we get the following results:

    I z = t(2(3t) 2 + t(2t 2) + 4 t 3 /12 + 2t(2t 2)/24 + 3t 3 /(24 12) = t 3 (18 + 2 + 1/ 3 + 1/3 + 1/96) = 1985t 3 /96 = 20.67t 3

    I x = t(2(3t) 2 /24 + t(2t 2)/24 + 4 t 3 /(12 24) + 2t(2t 2) + 3t 3 /12 = t 3 (18/24 + 2/24 + 1/72 + 8 + 6/24) = 655t 3 /72 = 9.1t 3

    If the elastic moduli were the same in all directions, then the moment of inertia about any of the axes would be:

    I" x = t(2(3t) 2 + t(2t 2) + 4 t 3 /12 + 2t(2t 2) + 3t 3 /12 = t 3 (18 + 2 + 1/3 + 8 + 1 /4 =43 3 /12 = 28.58t ​​3

    Thus, if we do not take into account the presence of glue and other factors listed above, the ratio of elastic moduli would be 20.67/9.1 = 2.27, and when considering a plywood sheet as a beam, the elastic modulus along the fibers of the outer layers would be (20.67/28.58)10 5 = 72300 kgf /cm 2. As you can see, the technologies used in the manufacture of plywood make it possible to increase the calculated value of the elastic modulus, especially when the sheet bends across the fibers.

    Meanwhile, the ratio of the calculated resistances when bending along and across the fibers of the outer layers (which can also be considered as the ratio of moments of inertia) is much closer to what we determined and is approximately 2.3-2.4.

    Sometimes clients ask us: “Do you have OSB plywood for sale?” And then we politely explain that this is not a completely correct term. There are two different wood-based board materials: plywood and OSB board. Their characteristics are similar in some ways, but different in others, and our task is to choose suitable material depending on the requirements that are placed on it.

    Before answering the question “which is better: plywood or OSB?”, you need to decide on a large number of parameters that influence the choice of one or the other material.

    I would like to immediately note that there are four types OSB boards, which differ in their parameters, areas of application and cost. We will compare with plywood, which is most common in Russian market building materials.

    We will try to objectively evaluate and compare different indicators so that the buyer can choose the most suitable one from the two materials.

    Strength.

    Many companies selling OSB are a little disingenuous in their advertising, declaring that OSB boards have the same strength characteristics as plywood. To put it mildly, this is not entirely true. If we look at GOST 3916.1-96 for plywood, we will see that the tensile strength during static bending along the fibers of the outer layers of plywood must be no less than:

    Birch plywood FSF - 60 MPa (or N/mm2), birch plywood FK - 55 MPa, coniferous plywood FSF - 40 MPa, coniferous plywood FK - 35 MPa.

    The highest value of the bending strength of OSB along the fibers of the outer layer is 22 MPa.

    Thus, even coniferous plywood is superior to OSB-3 board in terms of strength.

    Moisture resistance.

    We will compare moisture resistance by such an indicator as swelling in thickness after immersion in water.

    Swelling in thickness when immersed in water.

    TDV TDV EN-317

    OSB-3 (Egger)

    FSF coniferous plywood (Perm plywood mill)

    within 24 hours (%)

    within 30 days (%)

    Price.

    The idea of ​​introducing OSB boards to the market was to find a cheaper and not much inferior alternative to construction plywood. In the USA, Canada and European countries, this idea is being implemented. The production of OSB boards has not yet been established in Russia, and imported products often cost more than plywood due to customs and logistics costs. Logically, having a lower cost, OSB should cost less than plywood, but in Russia this principle is still being violated.