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How to install joists on the floor under plywood. How to level the floor in a house with plywood along the joists - instructions with photos and videos

How to install joists on the floor under plywood. How to level the floor in a house with plywood along the joists - instructions with photos and videos

All photos from the article

Installing a plywood floor using joists is currently recognized as the most convenient, fastest and inexpensive type of rough or finishing coating in a house. The unique characteristics of the materials allow the entire range of activities to be completed relatively quickly and efficiently, even by a person who has only general basic skills in working with wood.

Today we will talk about the main points of this process.

Preparation of tools and material

Any construction work begins with careful preparation. The more carefully you pay attention to this process, the easier and faster the main work will be completed, and most importantly, at the finish you will receive a high-quality coating.

A few words about the instrument

Fortunately, for such work you do not need highly specialized and expensive tools.

As a rule, a standard set that almost every good owner has is enough:

Most construction and installation work cannot be done without an electric drill; in this case, it is better to get a hammer drill;

Naturally, you will need a hammer and a screwdriver, or at least a set of screwdrivers;
Since we are talking about working with wood, we cannot do without a hacksaw. Of course, plywood can also be cut with a hand saw for wood, but believe me, sawing with your own hands is quite difficult and time-consuming, so it’s better to immediately take a jigsaw;

In addition, if you are going to make a finished plywood floor using joists, then for finishing you will need a normal sanding machine;
You will need to draw the horizon, so in addition to the usual building level, you should also take a liquid level, working on the principle of communicating vessels.

Important: experienced builders strongly do not recommend cutting plywood sheets or wooden beams with a grinder. This tool is not intended for working with wood; the risk of injury is too great.

Preparation of lag

Theoretically, the sheets can also be fixed to a structure made of a metal corner or I-beams, but this is much more expensive and more problematic to install, so we recommend using exclusively wooden beams.

Before installation, the beam must be treated with an antiseptic and water-repellent compound; in a budget option, it is enough to cover it with several layers of used machine oil.

The cross-section of timber for floor joists under plywood is selected depending on the thickness of the insulation in the subfloor. If insulation is not planned, then a 50x50 mm block will be enough for the screed. For underfloor heating or concrete insulation, 100x50 mm timber is sufficient.

When it comes to installing floors on the first floor, the thickness of the insulation there can reach up to 250 mm, and accordingly the timber should be no less. The width of the horizontal plane on which the flooring will be attached is taken from 50 mm.

Plywood selection

The question of which plywood to use for floor joists is far from idle; the modern market provides a fairly wide choice and the price is not a guarantee of quality. After all, many expensive types of material are, in principle, prohibited from being laid in residential premises.

The first thing you should pay attention to is the grade of the sheet.

It consists of a letter abbreviation and displays the type of adhesive used in the production of plywood.

A finished or subfloor made of plywood on joists must not only be durable and reliable, but also safe. At the moment, the most popular material for residential premises is considered to be sheets of the FC brand. It has an optimal price-quality ratio and is even approved for use in children's rooms. The adhesive used here is urea-formaldehyde resin. But it has one flaw: this coating is not moisture resistant;

Flooring made from FC sheets is perfect for a living room, bedroom or storage room. Waterproof plywood is needed in the kitchen, hall and bathrooms. And here you can choose. There is an option to lay “FKA” sheet; it is based on an albumen-formaldehyde composition. You can take yacht plywood under the FB brand; it is more expensive, but can withstand even prolonged exposure to sea water.

Advice: what you definitely shouldn’t do is buy “FSF” sheets. They contain some phenolic compounds. And phenol, as you know, is considered a toxic carcinogen. The only place where such sheets are suitable is the lower cladding of the subfloor in a wooden house, the layer that is mounted immediately above the ground.

Next, you should decide what thickness of plywood for the floor joists is suitable in your case. It is faster and easier to make rough flooring from a sheet with a thickness of 20 mm or more. Its stability and strength are quite sufficient for a single-layer coating. In addition to high strength, single-layer flooring conducts heat much better, which is important when installing heated floors under laminate or tiles.

If you are installing a deck in a wooden house, then the approach should be slightly different. Such houses are prone to shrinkage and seasonal deformation, so it would be appropriate to make a floating, two-layer coating from sheets of 10 - 12 mm. The total thickness of the plywood on the joist floor will remain the same, but such flooring is no longer afraid of deformation of the base.

Advice: if you plan to finish the floor from plywood, then it makes sense to immediately buy sanded sheets. So after installation you will only need to sand the joints and fastening points. In the marking it looks like “Ш1” or “Ш2”, which means the sheet is sanded on one or both sides.

As for grade, it is now divided into 5 positions:

Extra or E class comes with no flaws at all;
The first grade has minor cracks, but no knots. These two grades are used for finishing;
The second and third grades are perfect for rough flooring; there will be a certain number of knots and small cracks in the top veneer, which in our case is not so important;
The fourth grade is considered technical; it has no restrictions on defects, although you can take it for a subfloor, but you should carefully examine each sheet, especially if the product came from friendly China.

Tip: there is deciduous and. Theoretically, any material can be used for a subfloor, but coniferous material, although considered less durable, is better suited in this case, since it is more water resistant and, most importantly, costs less.

When repairing floors, many questions always arise. This is not surprising if you have such nuances, because the floor is a part of the house that is used almost around the clock. There are many options for making this part of the home comfortable, but you need to dwell in detail on how to build a plywood floor along the joists.

The process of laying a plywood floor at the stage of fastening to the joists.

This type of coating is perfect if you need to do insulation, but it is impossible to fill a cement-sand screed, and even if there are large uneven areas.

The bars that form the sheathing when installed are called lags. With their help, the surface in the room is leveled, and they also serve as a basis for attaching sheets. They can be made of metal or concrete, but the use of plywood requires the use of wooden blocks.

The construction of the floor will not be practical enough without lathing, since it gives the necessary rigidity to the sheets. Of course, there is a way to lay plywood without lathing, but this type of fastening can only be used if the room has a flat base. Without this, leveling the floor with plywood without joists will not be done well.

Laying joists on the street. First, they build a frame and connect the sections together.

For logs, timber with a cross section of 50×100 mm is usually used. The rectangular shape is necessary so that the sheets can be joined on the wide side. In other words, if you don't have a support pad, attaching the sheet will be difficult.

Also, before the logs are installed, they must be treated with antifungal and fireproofing agents.

Pros and cons of choosing plywood

To the question: why is this particular material chosen to make an even coating indoors? The answer can only be given if you know its characteristics. The first positive quality is durability.

Compared to chipboard and USB boards, plywood will last much longer. The reason for this is the technology of its manufacture. Unlike other types of wood boards, plywood is glued with veneer, which gives it strength. Three types of adhesives are used for gluing veneer, two of them are moisture resistant, so plywood can withstand moisture for a long time without destruction or rotting.

When using this design, additional communications can be installed underneath it without resorting to cutting niches in the walls.

Plywood is stronger than other floor coverings and will last much longer

The negative nuance is that this material is the most expensive of the entire group of wood boards. But, the opinions of experts always agree on one thing: it is better to do it once and for a long time than to redo it due to the use of low-quality materials.

What plywood to use for floor joists

In order to make a plywood floor using joists with your own hands, you need to know what type of plywood to choose. If you consider that water leakage is possible in places where heating radiators are installed, you should purchase a moisture-resistant type. Second and third grade worksheets are perfect. It is also necessary to take into account the size of the sheets. Size 1525x1525 mm or 2500x1250 mm would be the ideal solution. These dimensions are chosen in order to cut the sheet into four parts and use them for installation. If the work is carried out in an apartment located in a multi-storey building, it will be problematic to lift large sheets.

Types of plywood

Today the industry produces 5 types of plywood, which are characterized by class.

The first class is sheets that are sanded on both sides and have no flaws. They are used in the furniture industry;
The second and third classes are sheets that are polished on one side, while the second remains untouched. This plywood is multi-purpose;
The fourth and fifth grades are not sanded plywood. It is used for rough work.

The sheet's class can be identified by its seal, which is installed by the manufacturer.

Dimensions of unsanded birch plywood for flooring

Plywood is also divided into three types based on water resistance. This factor depends on the type of glue used.

Sheet thickness

The thickness of the plywood for the floor along the joists is also taken into account in the calculations. Thin sheets will sag, which will lead to destruction, and thick sheets will not be very comfortable to work with. But there is a way out of this situation, and moreover, it will play into our hands. The minimum thickness of floor sheets should be 20 mm. For a more durable coating and ease of installation, sheets with a thickness of 10 - 12 mm are used, which are laid in two stands. This creates a seamless coating.

With this technology, the plywood floor will be durable and reliable.

Step by step guide

At the initial stage of work, it is necessary to dismantle the old coating, if any. If laying a plywood floor on joists is carried out on a screed, then all cracks and potholes on it must be repaired. Then the entire perimeter of the surface to be sewn needs to be primed. After preparing the base, it is necessary to lay a waterproofing film. To do this, you need to spread it over the entire surface with a slight overlap on the walls.

The next step is to install the logs. Initially, the lags must be fastened around the perimeter of the room. To do this, a joist level is marked on the wall. If you have a laser level, then there is no need for marking. With this device, alignment can be carried out at the installation site. All our logs will be installed on substrates made of pieces of plywood or wooden blocks or boards. The substrates are installed along the line of placement of each log at a distance of 50 - 60 cm from each other. After installation at the level of one log, the substrate is fixed to the floor using dowels. You also need to remember that when installing substrates, under each of them you need to adjust a piece of old linoleum or roofing felt.

Preparing lags for further laying of plywood

It is important to note that the logs that are installed around the perimeter should not be in contact with the wall, that is, they are installed at a distance of 20 - 30 mm from each other. This placement is necessary for ventilation. After installing the logs around the perimeter, the remaining parts of the sheathing are installed. The distance between the floor joists under the plywood in our case is 70 cm. This distance was obtained by dividing the sheet in half. If sheets of other sizes are used, the distance between the logs will be different. For different cases it is 40 – 70 cm.

After installing the sheathing, insulation is laid between the joists. This can be polystyrene foam, mineral wool or expanded clay. As practice shows, the best option for the floor is mineral wool. It is not recommended to use polystyrene foam indoors due to harmful fumes, and expanded clay is less effective. Insulation mats should be cut 1 cm larger than the sheathing cells. When laying, such a mat will be tightly inserted between the sheathing bars.

After installing the insulation, the next step is to install a vapor barrier. It needs to be secured to the joists using a stapler.

Tools for work

To perform all the work efficiently, you will need a tool such as:

Level;
Roulette;
Jigsaw;
Miter saw;
Hammer;
Screwdriver.

As can be seen from the list, all work generally requires hand-held power tools.

Sizing adjustment

In most cases, when it comes to installing flooring, the problem that arises is the unevenness of the walls. This nuance does not allow installing parts of the coating exactly along the joists. To do this, you will need to trim each part along a line parallel to the wall.

We fasten the plywood sheet so that there is a small gap at the wall

Marking and cutting are not carried out in a complicated manner. The sheet is placed against the wall so that the second edge lies strictly perpendicular to the joist. You will also need a rail that is aligned parallel to the wall. A cutting line is drawn along it. In this way, trimming is done around the entire perimeter. When adjusting the dimensions, it should be taken into account that there must be a gap between the wall and the covering.

Installation of the first layer

If it was initially decided that the structure would be laid in two layers, upon completion of all work with insulation and sheathing, you can begin laying the first layer - this is a subfloor made of plywood on joists. In order to do the installation correctly, you must first lay out the cut parts along the entire row.

They are attached to the joists using self-tapping screws. There should be a gap of 3 - 4 mm between the sheets. This gap must be sealed with sealant. This technological gap is required for expansion. The installation of the first row is carried out in this sequence.

It is worth noting that moisture-resistant plywood for the floor must be used for the first layer. To drill holes you need to use a tool such as a comfirmat. This attachment fits onto the drill and makes a hole for the screw heads. The screw head, when screwed in, will be recessed into the slab.

Second layer

When installing the second layer of flooring, all work is repeated, as when installing the rough one. An important point is that the sheets must be screwed together with mixed joints. For greater strength, the layers need to be glued together. This is done using construction glue. Installation of sheets must be carried out with the clean side. Thanks to this, upon completion of all work, a wooden covering is formed.

Renovating an apartment or a country house inevitably accompanies the lives of most people. And one of the most common problems that have to be solved in this regard is cold or insufficiently level floors. There are several ways out of this situation, one of them is to make plywood floors along the joists. Whether this will be done with your own hands or with the help of specialists, each property owner decides at his own discretion.

What are lags?

Logs are special wooden or polymer bars or sections of metal profiles laid on a concrete base, on top of which the base for the floor is laid. Metal is much easier to work with and is more durable than wood. But there is one significant drawback - metal, unlike wood, is critical to changes in ambient temperature, which can lead to the floor warping. In addition, they will cost less.

It is necessary to take into account that the most suitable species for making logs are coniferous species, especially larch. The parts must be of the correct geometric shape, smooth and without bends along the entire length.

Selection of base material

In order to level the floor with plywood along the joists with your own hands, you need to choose the right material, since not every type of material is suitable for this. There are the following types of floor leveling sheets:

Plywood is a multilayer material, the number of layers starts from three.
is an excellent material for leveling wooden floors for subsequent laying of tiles. It is made from shavings and Portland cement with the addition of chemical ingredients.
Oriented strand board (OSB) is a multilayer material in which the chips are glued together with resins with the addition of synthetic wax. Eco-friendly, but bends easier than plywood and is a little more expensive.
(chipboard) has the lowest strength and environmental friendliness.
Fiberboard (Fiberboard) is a material made by hot pressing of wood fiber, very flexible and fragile.

Based on the listed properties of the materials, we can conclude that a do-it-yourself plywood floor on joists in a private house is best made from OSB, DSP or plywood.

About the material

Plywood is the most acceptable option. It consists of veneer sheets glued together in a special way: each new layer has fibers located perpendicular to the fibers of the previous one, which significantly increases rigidity. Plywood varies in characteristics of moisture resistance, durability and environmental friendliness, which depend on what binder material was used in production:

The FK brand is made using urea glue, is poorly resistant to moisture, and swells quickly. But it is safe for humans and can be used in rooms with low humidity.
The FSF brand contains phenol-formaldehyde glue, is moisture resistant, but not environmentally friendly due to phenolic emissions.
FB brand is bakelized plywood, resistant to moisture and aggressive environments.
FOF is a laminated (layer-pressed) material called laminate. Used as a decorative floor finish.

To make a plywood floor along joists with your own hands in a country house or in an apartment, plywood of the FK and FSF brands made of birch with a thickness of ten to fifteen millimeters is best suited.

Advantages of plywood flooring on joists

The installation of such a floor has a number of undeniable advantages:

strengthening soundproofing characteristics;
increase in thermal insulation qualities;
high-quality quick insulation of the floor by laying heat-insulating material between the joists;
ensuring uniform distribution of pressure on the base;
the presence of empty space between the logs makes it possible to locate various communications in it;
quick leveling of floor surfaces;
good strength characteristics of the coating;
possibility of easy replacement of damaged parts;
Even a beginner without special skills can handle the job;
installing a plywood floor on joists does not require specialized heavy equipment or tools.

Preparation for installation

Mandatory measures before laying floors should be:

inspection of the base;
thorough cleaning of large irregularities;
covering cracks and cracks;
floor waterproofing.

Whatever moisture resistance coefficient plywood or any identical material has, it has a certain hygroscopicity, which leads to the absorption of a certain amount of moisture. Therefore, the main stage of preparation is waterproofing. It is usually done with thick plastic film (in the simplest case) or a special coating. The concrete floor is completely covered with material, with a slight overlap on the walls. And so that after the film speaks for it. Parts of the waterproofing at the joints are secured with construction tape.

To install floors on plywood joists, galvanized hardware is used for fastening, with a length exceeding three times the thickness of the sheets being fixed.

Which is better: two thin layers or one thick one?

Plywood is a composite material. The layers in it are arranged crosswise with fibers to achieve sufficient rigidity and strength. Based on this, it becomes clear that in order to improve such characteristics, it does not matter at all how many layers are laid - two ten-millimeter layers instead of one twenty-millimeter layer or a greater number. And there won’t be a particularly big gain in price.

But when leveling very crooked floors, the number of layers plays a significant role here. When laying one layer, the unevenness will, of course, be smoothed out, but differences will remain at the joints of the plywood sheets. This is where a correctly laid second layer will help - the joints of the slabs of each of them will coincide with the center of the slabs of the other layer.

Conclusion: to insulate a flat base, you can install plywood floors along joists with your own hands in one layer with sheets twenty millimeters thick. When leveling a crooked base, two ten-millimeter layers with plywood slabs laid in a checkerboard pattern are better suited.

Do-it-yourself plywood floors on joists: joists and sheathing

The sequence of steps in this stage is as follows:

To perform the installation, use dried, flat beams with a cross-section of 10 x 5 cm and a length of at least two meters. In addition, they must be kept indoors for two weeks.
Waterproofing is laid on the prepared base, and the beams are treated with an antiseptic.
When installing the logs, an indentation of 25 mm is made from each of the walls.
To neutralize unevenness, use MDF or fiberboard substrates with a side of a square of 20 cm, and linoleum pieces to suppress noise. In places where there are substrates, the logs are attached to the cement base with anchor bolts. When laying, leave a distance of 40 cm between the joists.
When all the logs are installed, they move on to installing the sheathing. Its strips are also installed on substrates and secured to the floor and joists with self-tapping screws at a distance of no more than half a meter. It is important that the size of the sheathing matches the parameters of the plywood sheets.
The resulting cavities in the sheathing are filled with insulation and sound insulation.

Sizing, fastening

In order to properly install plywood floors on joists with your own hands (photos of the actions are presented in the article), you need to cut the plywood into sheets of the required size, optimally 1250 x 2500 mm. For convenience, they can be numbered.

To eliminate the possibility of squeaking during further use, strips of glassine are stapled to the joists before laying the plywood.

The sheets are laid across the joists, secured with screws at a distance of 15 cm. At the joints, the screws are placed in a checkerboard pattern at a distance of 10 mm from the edge of the sheet.

During installation, a gap of about a third of a millimeter is left between the sheets, which is then filled with sealant or elastic mastic and glued with moisture-resistant glue.

Laying begins from the window, the heads of the hardware are completely recessed into the plywood into the drilled holes. If communications are planned, cutouts are made for them.

Do-it-yourself plywood floors on joists: installation of layers

This stage is performed in the following sequence:

Laying the first layer begins from the window with a distance of about half a centimeter from the wall. You can use plywood of the third or fourth grade, since the presence of knots and appearance do not play a noticeable role due to further finishing, and the cost of such material is much cheaper.
Intermediate logs can be an addition to plywood. This is necessary to reduce the size of the cells in order to ensure a good connection between the sheets and the frame. To do this, the logs are connected with crossbars made from scraps, screwing them with steel corners. The size of the cells should be a multiple of the plywood sheets so that their edges always lie on the joists.
The second layer of sheets is mounted offset from the first. The layers are fastened together with self-tapping screws and glued together with PVA or special glue for plywood.
Seal the seams between the sheets.
After laying the last slab, the surface is sanded with sandpaper manually or using a sanding machine.

Using the same principle, you can install a plywood floor along joists with your own hands on the 2nd floor of a private house.

To successfully complete the work, you must pay attention to the following:

It is not recommended to lay tiles on plywood: they may fall off due to the expansion of the wood layer.
Uneven surfaces on the screed can be sprinkled with sand, and cracks and holes in the corners can be foamed.
To check the humidity in the room, you need to cover the base with plastic wrap for a day. If perspiration appears underneath, waterproofing is a must.
It is important to follow all installation rules when installing a plywood floor on joists with your own hands. In a wooden house on the ground floor above the ground, this is especially true - if the technology is not followed, the entire coating will have to be removed to correct errors.
To ensure good sound insulation, the logs are not fixed rigidly, but are installed on felt or rubber pads to dampen noise.
Before starting the installation of the logs, find the zero level and then level the remaining beams along it.
The insulation must be cut strictly to the size of the cells so that its edges do not bend during installation.
After laying the insulation, a vapor barrier membrane can be attached to the joists with a stapler.
For installation, it is better to use not ordinary hardened black self-tapping screws, but yellow wood screws with a powerful mounting hole.
The sheets must be laid so that not cross-shaped, but T-shaped joints are formed.

Conclusion

When properly installed, a plywood floor can last more than twenty years. Just remember that this material is suitable for installation in dry and warm rooms.

It is also worth noting that plywood is suitable not only for arranging wall cladding and subfloors. Craftsmen use it to create unique decorative compositions in the interior. Using an old skill - artistic sawing, pictures are laid out from pieces of plywood and parquet is formed.

Dry prefabricated floor screed is most often made from plywood sheets. It is believed that this is an ideal base for any type of flooring, including linoleum, laminate, carpet and even ceramic tiles. A high-quality and durable plywood floor on joists requires attention to the nuances and compliance with the basic rules specified in SNiP.

Which plywood to choose

Plywood is a multi-layer wood-sheet material that is made by cross-gluing an odd number of layers of rotary-cut veneer. For production, birch raw materials or technical grade conifers are most often used, less often - oak, beech, linden and others.

Advantages of plywood:

high mechanical strength to any load;
relatively light weight;
low thermal conductivity coefficient;
acceptable level of humidity (8–12%), which allows the use of some types of plywood in damp and unheated rooms: kitchens, bathrooms, balconies, loggias, etc.;
use in combination with water- and infrared-type “warm floor” systems.

The disadvantage of sheet material is that the production uses adhesives that are unsafe for human health. As a rule, products are assigned an emission class of at least E1.

Plywood products are classified according to the following criteria:

Scope of application.

The areas of application of sheet material are limitless - from construction to electrical engineering. But to form a prefabricated screed or finished floor, it is recommended to use structural and construction varieties.

Brand.

This parameter is determined by the type of adhesive used. Let's consider three basic types:

FSF (plywood glued with phenol-formaldehyde resin glue). The product is considered moisture resistant and is used for finishing rooms with normal and high humidity levels.
FC (plywood glued using urea-formaldehyde glue). Refers to products with average moisture resistance, recommended for use in dry rooms.
FBA (plate on albumin - casein glue). Positioned as a material of limited moisture resistance.

Variety

According to GOST 3916.1–96, products differ in the number of permissible defects and defects of wood, as well as defects during processing. There are five degrees of quality:

E – extra or elite. The product is made of oak, alder, birch and other species, has a perfectly flat, smooth surface, without the slightest defects. Slight deviations in the structure of random wood are allowed.
I – pin and healthy light or dark knots are possible – no more than 3–5 pieces. for every square meter of surface. Cracks (except for closed cracks) and other types of defects are excluded.
II – healthy, partially fused, unfused and falling out knots with a diameter of up to 6 mm, wood inserts and open cracks up to 200 mm long and no more than 2 mm wide are allowed.
III – there are: a) wormholes and holes from fallen knots with a diameter of up to 6 mm in an amount of no more than 10 pieces. per 1 m² of area; b) diverging cracks with a length of 300–600 mm and a width of up to 5 mm (subject to sealing with putties or sealants); c) dents and scallops.
IV – surface with all kinds of defects: from fused and fallen knots without limiting the number to defects along the edges up to 5 mm deep.

For subfloors on joists, as a rule, sheet material of grade 1–4 quality is used. Please note: Plywood is usually double marked, such as 1/2 or 2/2. Matches the grade of each side. That is, a product of class 1/3 is characterized by the fact that one surface is assigned category 1, and the second - 3.

Nature of processing.

Sanded and unsanded plywood.

Plywood boards can be sanded or unsanded. Marked:

Ш1 – processed only on one side.
Ш2 – polished on both sides.
NS – unpolished.

Laying the floor along the joists is done using slabs of any type. But common sense dictates that it is better to use products that are polished on at least one side. This will allow you to create the most even and smooth floor for installation of linoleum, laminate, etc.

Dimensions.

The length of plywood sheets can reach 6 m, width 3 m, and thickness starts from 3 mm. For roughing and finishing work on horizontal bases, the following material is used:

1525x1525 is the most commonly used size for floor joists. The amount of waste is small and convenient to transport.
1210x2440 – for leveling bases in multi-storey buildings of standard series with elongated room shapes.
500x3000 - convenient in multi-storey or commercial new buildings, where the principle of studios or open plan is implemented.

The optimal thickness of plywood for floor joists depends on the type of prefabricated screed and the level of load. If you plan to install in two layers, then it is better to choose products with a cross-section of 8–12 mm, and for single-layer installation – 8–22 mm.

Joists and fasteners

According to SNiP 3.04.01–87 (SP 71.13330.2017) “Insulating and finishing coatings”, chamber-dried wooden beams with a humidity of 12–18%, without cracks, bark and traces of rot, are used to form the floor along the joists. In this case, the length of the abutting supports must be at least 2 m, thickness - from 40 mm, and width - 80–100 mm.

Although many experts recommend purchasing slats with an aspect ratio of 1:1.5 and 1:2, in practice, logs of 50x40, 50x50, 50x70 and more are most often used. Moreover, the height of the supporting elements depends on various parameters: the load level, the cross-section of the insulation used, the maximum floor height and even the personal preferences of the customer. There are no universal recommendations; components are selected in each case separately.

To equip a load-bearing frame in apartments and private houses, you need the most even, durable timber made from inexpensive species: pine, spruce. If finances allow, you can purchase products made from larch, aspen, and alder that are resistant to changes in humidity.

Do not forget that wooden structural elements are not highly bioresistant. Therefore, they must be treated with fungicidal and hydrophobic agents. This will significantly increase the service life of the entire floor structure.

It would be useful to mention the support elements for the logs. Building codes do not recommend the use of wooden wedges and bosses due to the fact that the material easily changes shape with changes in humidity. When installing on a concrete or plank floor, mineral screed or point supports under the timber, it is better to lay strips of hardboard.

In practice, many craftsmen prefer to lay pieces of OSB, chipboard, MDF or moisture-resistant plywood on the floor. The minimum size of the lining should be 10x10 cm or 10x15 cm, the interval between them should be at least 30 cm.

Laying joists on glued plywood pads.

As an alternative, which is insensitive to moisture, you can use special support and fastening elements with an anti-corrosion coating, designed for the installation of adjustable floors.

Let's consider another important component of the floor structure - hardware. In addition to the joists, you will need fasteners to secure them to the base, as well as to attach sheets of plywood to the frame. These can be anchors, nails, universal or self-tapping screws, metal corners, etc.

The range of fasteners is huge. To fix the pads or the joists directly to the concrete base, dowels are most often used - threaded nails with a diameter of at least 6 mm or mechanical-type metal anchors. The former are cheaper, but the latter provide more reliable and durable fixation of the slats to the base.

An example of fixing joists to the floor with corners.

Anchor fasteners for concrete and brick are made of high-quality alloys - brass, stainless steel. It consists of a spacer or working sleeve (changes dimensions when forming a connection) and a non-spacer part - a rod. To mount the frame to the base, a hole is drilled in concrete with a diameter equal to the cross-section of the sleeve or 0.5 mm less than it. When hammered or screwed in, the mounting post pushes the sleeve inserted into the channel. And due to this, it is firmly fixed in concrete.

The dimensions of the hardware product depend on the dimensions of the supports. For the installation of underlay elements made of chipboard, plywood, OSB, as well as wooden logs, products of category M 6 are most often used – M 12, that is, with a rod or wedge diameter from 6 to 12 mm. The length is selected based on the thickness of the joists and/or support supports, taking into account the depth of insertion into the concrete of 5 cm or more. The approximate interval between fasteners is 30–60 cm.

To rigidly attach pads or joists to a wooden subfloor, you can use wood screws with rare threads or universal galvanized ones with a diameter of 4 mm or more. The distance between hardware is at least 30 cm, screwing depth is from 30 mm.
To attach plywood to joists, it is most convenient to use special self-tapping screws for gypsum fiber boards and chipboards or universal galvanized ones. The first ones differ from the standard ones by mixed screw threads and notches on the cone-shaped head, which provide countersinking. The length of the hardware should be 2–2.5 times the thickness of the coating, the diameter should be 3.5 mm or more.

It is not recommended to use black hardened wood screws for plywood on joists. Practice shows that with seasonal changes in geometric dimensions, this type of hardware breaks under load, and the structure “loses” its rigidity.

You can also use regular nails with a cylindrical shaft and a sharp end. The efficiency and speed of work will increase several times if you use fasteners not in bulk, but in a cassette designed for nailing. The product is often aimed at the base or supporting frame at a distance of 15–25 cm.

Step-by-step instruction

To install a prefabricated screed yourself, you will need:

Sheets of plywood of suitable thickness.
Wooden logs.
Lining material for leveling the base.
Antiseptic primer.
Hardware.
Soundproofing and/or thermal insulation with components.
Repair compounds for partial restoration of damaged foundations.
Waterproofing.
Damper tape.
Silicone sealant or elastic wood putty.
Tape measure, marking pencil, metal ruler or lath.
Drill/screwdriver or hammer/nail gun (nailer) with accessories.
Laser or water level.
Spatulas, brushes, rollers.
Construction vacuum cleaner.
Cutting tools with accessories for wood and plywood (circular saw, jigsaw, etc.).
Grinder machine.

The technology for installing prefabricated screeds is partially presented in SNiP 3.04.01–87 (SP 71.13330.2017) “Insulating and finishing coatings.” In accordance with the recommendations of these standards, installation is carried out in 4 stages.

Preparation

Any repair begins with cleaning the base from debris, dirt and dust. It is advisable to remove oil, bitumen and similar stains, traces of soot and soot from the surface.

No professional will begin work without partially repairing the damaged areas. Rotten, damaged elements of the wooden flooring must be replaced, and cracks and loose areas of the mineral base must be restored. To do this, you need to open up the cracks, remove dust and fill with repair compounds. If possible, it is better to clean off fragile sections, and smooth out the resulting pits using cement-sand, self-leveling and other quick-drying mixtures.

If necessary, the floor is waterproofed. It is needed if:

it is necessary to protect the structure from residual moisture of the concrete base;
there is a cold basement under the ceiling;
the floor on joists is installed in the bathroom and the room located on the floor below should be protected from possible leaks.

To create waterproofing, the entire available range of materials is used: films, membranes, rolled adhesive products, coating compounds, painting agents, and the like.

In some cases, soundproofing of the base is required. According to the rules, the acoustic layer is laid between the base floor and the screed. Therefore, sound-absorbing mats are laid under the logs. If sound-insulating mineral wool (stone or glass) is used, then it must be laid in the openings between the joists, and the support rails themselves must be fixed using point acoustic pads.

Laying logs on acoustic pads.

It is advisable at this stage to treat the timber, bosses and other wooden structural elements with antiseptic impregnations.

Formation of a power frame

The frame of logs can be formed in the form of longitudinally located beams or as a single or double sheathing. Of course, the second option creates more reliable support for the plywood.

SNiP 3.04.01–87 (SP 71.13330.2017) recommends laying slats across the light flow, and in corridors and other rooms with a certain direction of foot traffic - perpendicular to the movement. Of course, in the future the frame will not be visible under the coating, but the essence of the advice is different. The developers of the building code determined that if the frame is formed across the most intensive movement of people, then the loads will be distributed over the majority of the supports of the load-bearing frame, and not among 2–3 elements. Or even worse - between them.

First of all, the zero mark is identified, relative to which the supports are aligned. Next, the beacons are mounted under the joists or the required level is stamped on the wall with thread and dye. But the most convenient way to construct a reference line is a laser level with a plane builder.

If sound insulation is required, before installing the supporting frame, it is necessary to lay acoustic material on the base: slabs, membranes, rolled products.

Now you can begin installing the logs, observing all the necessary gaps:

Between the outer batten and the wall - at least 20 mm.
Between adjacent supports - from 30 cm, but not more than 50 cm. We remind you: the higher the load on the floor, the more frequent the logs should be.
Between the ends of one row – 0–0.5 cm.

For leveling, spacers made of chipboard, OSB, MDF, etc. are installed under the frame elements. After checking with a level, the bosses or backing boards are attached to the base dowel - with nails, screws or anchors.

Plywood linings.

Joists on wooden bosses.

To drill holes for hardware in underlay components, joists and plywood, you should purchase feather or special wood drills with a countersink.

Many craftsmen recommend laying damper layers on firmly fixed supports. Such a preventive measure will prevent the structure from starting to creak in the future.

The penultimate step is to fix the joists over the entire area of the room using suitable hardware. Please note that a wide strip should be laid in doorways, which will protrude beyond the partition by 50–100 mm on each side.

For maximum leveling accuracy, you can use fastening and supporting hardware designed for adjustable floors. Essentially, these are powerful anchors that are installed in the floor slab. The adjusting nuts are screwed onto the main bolts, then the beam is placed and secured with a lock nut. The excess anchor rod is cut off with a grinder or a metal saw.

Laying plywood boards

The most controversial issue is the thickness and number of layers of plywood. There is no single correct opinion. It is clear that the higher the expected load on the floor (weight of furniture, intensity of foot traffic, etc.), the greater the thickness of the slabs should be and the smaller the distance between the joists. This will avoid sagging of the structure and its damage.

What type of flooring is best - single or multi-layer? There is no clear answer to this question. Each type has its own advantages and disadvantages. But the total thickness of the plywood flooring must remain constant - at least 18 mm.

Installation of slabs begins with their preparation. You should cut them to the required sizes, make cuts for communications or enclosing structures of complex shapes. Then a preliminary arrangement is carried out. The first row is laid out from the far corner along a solid wall.

If necessary, plywood sheets are adjusted, drilling points for hardware are marked with a distance from the edge of 2–3 cm and an interval between fastenings of 15–30 cm. An expansion joint of 0.4–1 cm must be maintained between the plates, as well as between the plates and the walls.

After one row of plywood is drilled and the sawdust is removed with a vacuum cleaner, the sheets are fixed with suitable fasteners. Experienced craftsmen recommend starting to screw in hardware from the center of the slab, gradually moving diagonally to the edges, and then along the perimeter. This approach will straighten the plywood and avoid waves. Do not forget that the hardware must be “recessed” into the plywood by at least 0.2 centimeters.

The second and subsequent rows are laid in compliance with the rule that the seams are offset by at least 1/3 of the length. If plywood is installed in two layers, then the joint areas of the first layer should not coincide with the seams of the second.

Finishing the floor

After installation, professional craftsmen recommend “walking” the surface with a grinding machine with an abrasive attachment from 80 to 120 units to eliminate the slightest differences between the sheets. After this, the flooring is cleaned of dust and sawdust, and the seams are filled with sealant or elastic wood putty.

It is not advisable to use polyurethane foam for seams, as it begins to sag and crumble over time.

A plywood floor can be installed even without extensive work experience, sophisticated equipment or construction education. For clarity, we recommend watching videos from professionals.

Leveling the floor before finishing is done using various materials. Laying plywood on a load-bearing structure made of joists is one of the simplest techniques. Even a beginner can perform all technological operations without assistants and consultants, with his own hands. All the features of installing a plywood floor will be discussed in this article.

On a note! Not every plywood sheet is suitable as a subfloor. Not only the quality of further finishing, its durability, but also the microclimate in the room largely depends on the correct choice of product variety. And with lags it’s not so simple.

Selection of materials

Plywood

To install floors, it is advisable to purchase sheets (taking into account the cost) marked FC (up to 3 years of guaranteed operation) or FSF (increased water resistance - up to 5). Different types of wood are used in the production of veneer. Birch is considered the best for plywood.

When fastening veneer, adhesives are used, which differ in their chemical composition, and therefore in the degree of toxicity (depending on the type of product). Therefore, FC sheets are recommended mainly for installation in residential premises, and FSF (as less “environmentally friendly”) - in all others (although preferably only outside the building, for example, for arranging a continuous roof sheathing).

Since the cost of the material is determined, among other things, by its thickness, it is worth dwelling on this issue. The strength of the structure depends on this parameter of the rough coating, the interval between the lags and the number of layers. Therefore, you can combine. Still, in any case, it is not recommended to use anything thinner than 10 mm.

On a note! Most often, logs are installed at a distance of half a meter from each other, since this scheme simplifies working with insulation. For it, you should select plywood with a thickness of 15 mm, maximum 18 (this depends on the expected load on the floor). It is much more difficult to work with more massive samples.

Helpful Tips:

To reduce the cost of flooring, you should limit yourself to 3 or 4 grades of plywood. It costs much less, and the appearance of the sheets does not matter in this case, since they will be covered with finishing material.
A pre-drawn layout of the room will also help with this. Using it, it is easy to determine what dimensions of sheets are best to purchase. The most common (m) are 1.5 x 1.5 and 2.4 x 1.2. The less you have to cut, the more material will be used for its intended purpose. Consequently, the amount of waste will be reduced. Perhaps, given the complexity of the geometry of the room, it is advisable to purchase plywood with different linear parameters.

Lags

There are only 2 options - made of wood or metal profiles. The latter are easier to work with, and in terms of durability, they are preferable to wooden blanks. The arguments are significant, but they do not take into account one nuance - the temperature deformation of materials. For them, this coefficient should be approximately the same. From this point of view, in order to prevent warping of the floor and the formation of cracks, it is advisable to lay plywood (taking into account its structure) precisely on wooden logs.

The samples must have the correct geometry along the entire length (without bends), otherwise the process of leveling the floor will be significantly more complicated.

It is also important what kind of wood the workpiece is made from. Since the logs will not be in the most favorable conditions (certain dampness under the floor cannot be avoided), you should focus only on coniferous trees, and first of all, larch. Of all the breeds that are most resistant to moisture, it is the cheapest. It is worth recalling that it was not for nothing that in the old days it was used to lay the bottom row (crown) of a log house.

Fastening parts

Naturally, we can only talk about galvanized hardware. But with what parameters? There is a general rule. The length of the fastener must exceed the thickness of the sample being fixed by 2.5 - 3 times.

Operating procedure

Even if plywood is laid on existing joists, instead of dismantled floorboards, it is advisable to familiarize yourself with the full range of measures. Perhaps, taking into account this information, the idea will arise to redo something, improve it.

Waterproofing concrete

The author deliberately skips such activities as cleaning the base, inspecting it, eliminating defects in the form of cracks and crevices - these are the basics of repair.

No matter how moisture resistant plywood is, it is characterized by a certain hygroscopicity. Consequently, gradual absorption of moisture cannot be avoided. If a protective layer has not been installed before, then this should definitely be done. What to use is decided depending on the specifics of the room and the financial capabilities of the owner. Perhaps the cheapest option is P/E film (thick).

The entire concrete floor is covered with it, with small turns onto the wall so that the material protrudes somewhat above the subsequently laid plywood (depending on its thickness). These edges will then still be covered with baseboards. The joints of the canvases are sealed with tape (construction tape).

If the protective layer was not installed before, then you will have to think what is simpler and more economically feasible - dismantle the logs and do everything from scratch, or purchase special impregnations (penetrating waterproofing).

Laying lags

The distance between the slats is selected taking into account the requirements for the strength of the floor, the dimensions of the sheets, their thickness, the size of the insulation material and a number of other installation features. But first of all, you need to focus on plywood. It is fastened with a distance of approximately 10 mm from the hardware from the edge (so as not to destroy the edges). The joint lines of the fragments should be located on the longitudinal axis of the joists (if possible).

Each experienced craftsman has his own procedure for installing logs. But a number of features should be pointed out:

It is advisable to attach the logs not to concrete, but to pre-set stands (according to the diagram). Firstly, the gap will provide better air circulation under the flooring. Secondly, adjusting the log height will be greatly simplified.
Work should begin from the walls. The indentation is about 25 - 30 mm. After checking the horizontal position, the outermost logs are securely fixed, and all the other intermediate ones are aligned with them.

To orient the log relative to the horizontal plane, a level (construction level) is used, but its body is short. This means that large errors cannot be avoided. To minimize them, it is advisable to mount the device on a rail. As a rule, it is enough for it to be 1.5 - 2 m (it will be extremely inconvenient to work with a larger one).

Fastening plywood

The first row (from the window) is laid out, the fit of all fragments is checked and drilling points are marked (the distance of the sheets from the walls is about 2 mm).
They are removed and processed one by one - holes are made for fasteners, countersinking is performed (synonym - reaming). This is necessary in order to completely drown the caps.

On a note! You shouldn’t be too “zealous” when trying to drive the self-tapping screw deep into the plywood with a screwdriver or screwdriver. This will cause cracks to appear in the head area.

The edges of the sheets are processed (at an angle). After connecting the fragments, a groove is formed, which is filled with sealant. Pros - partial improvement in the quality of insulation, sound and waterproofing of the subfloor. If necessary, holes are cut for laying communication routes.
Final installation of sheets in place and their fixation. Depending on the size of the fragment - along the perimeter (required) and crosswise (or only in the center).

To reduce the risk of plywood loosening, it is advisable to lay strips of roofing felt on the joists (on top).

Floor treatment

It consists of grinding the joints and sealing all grooves and holes (above the fastener heads) with sealant.

After this, you can begin finishing.