Thanks to adjustable joists, you can create a perfectly flat floor. Adjustable joists make it possible to do without such labor-intensive processes as concrete screed or self-leveling flooring. Moreover, even these technologies do not always give the result in the form of a perfectly flat floor. Covering on joists, which can be adjusted using stand-bolts, has many advantages and is optimal for finishing the floor.

Advantages of the method: adjustable floors on joists

Such a floor consists of logs, that is, beams and flooring made of plywood sheets and boards. The only drawback is that it is difficult to purchase ready-made adjustable joists - they will have to be built from purchased materials. But this is not difficult. After all, they are a beam drilled at equal distances with inserted bushings and supports made of polymer materials. Instead of plastic bushings and supports, you can install metal studs.

Adjustable joists make it possible to raise or lower the floor at any time

A properly executed design has the following advantages:

The floor can be raised up to 15 cm or more;
The process is quite simple and fast - 1-2 days;
Adjustable joists allow you to avoid the costly and time-consuming “wet” screeding process;
With this method it is achieved high efficiency alignment;
The ability to use technology in houses with weak wooden floors;
Besides flat surface The floor's thermal insulation and sound absorption are improved;
The underground space can be used for various communications.

It is of great importance that you do not need to use dirty technologies, and you can carry out the installation with your own hands.

How to Make Adjustable Plywood Floors

Plywood is a board pressed from several layers wood material- veneer, not wood chips. Therefore, it is quite durable, despite its low weight. Plywood floors are environmentally friendly, easy to use and easy to carry out work. This material can be used to make both rough and finished floors.

Adjustable plywood floors can be installed even on uneven surfaces

Installing an adjustable plywood floor has its advantages:

Cost-effective investment and speed of the process;
High thermal insulation qualities;
If a moisture-resistant material is selected, resistance to humidity;
Low abrasion, long service life.

When the ground has significant flaws, it makes sense to build a deck on legs using wooden beams.

First, the base is prepared, debris and dirt are removed. The surface is lined with any waterproofing material– film or rolled roofing felt. Logs made of wooden beams are installed taking into account zero level– its line must pass in exact accordance with the surface of the joist.

The timber is laid against opposite walls - the position is controlled using planks and then checked with a level. Threads are stretched between the lags, playing the role of beacons, intermediate beams are laid at intervals of 40 mm.

Plywood panels are adjusted and placed on supports. For fastening, a bolt or self-tapping screw with its full immersion into the material.

It should be borne in mind that to lay the entire system you will need a plywood sheet 2 cm thick. At the end, the surface is polished.

Design on adjustable joists you can do it yourself. Installation will consist of installing beams and attaching to them the primary, rough flooring under the base. The flooring is made from various materials, which, however, must have qualities such as moisture resistance and strength.

Before laying adjustable floors on joists, it is recommended to watch a training video

Usually a special, moisture-resistant type of plywood, DNT board or plasterboard is used:

If plywood is chosen, a finishing coating of parquet, laminate or linoleum can be made on top.
DSP or plasterboard with moisture resistance is more suitable for tiles.
If finishing coat assumes wood, it is better to use planed boards with grooves and tenons for ease and reliability of installation.

Lag technology allows you to significantly raise the floor level. This aspect is especially important when the house has poor sound insulation or it is necessary to install engineering Communication. However, in addition to logs, you can use slabs. They are best used to quickly level the floor or lay a thermal insulation layer. The slabs allow you to raise the floor only 3 cm.

To avoid squeaking in the future, there should be no dust or debris left on the floors, so it makes sense to use a vacuum cleaner for cleaning. Each stand must be installed firmly and not wobble, and all wooden and adjusting elements are securely fixed and attached to each other.

At independent work all basic principles should be adhered to technological rules and take into account the characteristics of each room.

Fastener Selection: Adjustable Floor Anchor

Adjustable floors can be built on metal studs or a special brass anchor can be used.

This method is especially suitable for those on a limited budget, because bolts can make work more convenient and simpler, but they are quite expensive.

Adjustable floor anchors may vary in diameter and length

Drive-in anchors and studs are more affordable and work well for installing an adjustable floor. For one adjustment link you will need an anchor - a collet, a metal pin, as well as two large nuts and washers.

The diameter of the studs must be at least 8 mm:

In this case, timber measuring 45x45 mm is used for the logs. It must be well dried and pre-treated with an antiseptic.
Bars the right size placed so that the gap at the walls is at least 5 cm, the intervals between them should be up to 40 cm.
Marks are made on the beams for placing the studs - the first is located 10 cm from the end of the log.
After the holes for the studs and nuts are made, the fasteners are installed. A recess is also drilled in the floor for mounting the anchor. This is done through a block and there is no need to mark the floor.
The anchors are inserted into the holes and the stud is screwed on. For reliability, two nuts are screwed onto the stud. This way it can rotate freely. The anchor is also secured with a nut.
After this, nuts, washers and the block itself are put on the studs.

Alignment adjustments begin with the outer studs.

Floor with adjustable joists (video)

Of course, making fasteners using a standard set of elements such as a wedge anchor is much easier, but under certain circumstances, studs and drive-in anchors can completely replace them. These fasteners are sold at any building materials store, and purchasing them is not difficult. And if the structure is made according to all the rules, such a floor can last a very long time.

An adjustable plywood floor can be raised to heights of 3-5 cm or 15-19 cm, depending on the designs of adjustable supports used. If you need to raise the floor to a small height of 3-5 cm, and it is impossible or impossible to arrange a floor screed according to the permitted load, an adjustable floor is made from plywood with plastic racks. To lift to a height of up to 19 cm, steel studs with supporting washers are used to support the plywood.

The design of the adjustable plywood floor does not allow for the use wooden logs, and the adjustable bushings screw directly into the plywood (plastic bushings) or go through the plywood (metal support pins).

Adjustable floor construction made of plywood with plastic studs

An adjustable plywood floor on plastic studs can be raised to a height of 3 to 5 cm. This is enough to lay water supply utilities, low-current and power electrical wiring under the floor.

For an adjustable plywood floor, moisture-resistant plywood with a thickness of 12 mm is used. Plywood is laid in two layers with offset. The first layer of plywood is directly adjustable in height using bushings, the second layer strengthens the floor structure.

The floor level is adjusted using a plastic post bolt and a bushing inserted into a hole in the plywood. 13 holes are made on a sheet of plywood measuring 1525x1525.

When calculating the finished floor level, the following are taken into account:

5 mm support washer;
2 layers of plywood 12mm each;
Total 24.5mm.

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Adjustable plywood floor construction on metal studs

A metal pin can be used to support the plywood sheets.

At the base of the floor, the stud is secured with an anchor dowel.
The plywood is supported by a large metal washer, the height of which is adjusted with a special nut.
The plywood is secured on top, also with a washer and nut.
A gap of 5 mm is left between the sheets of plywood of the first layer.
The second layer of plywood is laid offset and attached to the first layer with self-tapping screws.
A 5 mm gap is left between the wall and the second layer of plywood for ventilation.

We make an adjustable floor on joists instead of a concrete screed

Concrete screed, due to its structure, does not allow the formation of a surface that would be sufficiently smooth, and now, more and more often, mixtures such as “Betonite” or technology are used instead. A good alternative to all these “wet”, and therefore labor-intensive and dirty technologies, is a floor with adjustable joists.

These structures have special adjustable supports for the logs in the form of plastic post bolts. Moreover, the adjustable logs can be raised or lowered along the threads of these post bolts and thus easily adjusted to the level, which guarantees a perfectly level base for the finishing floors, and therefore no creaking floors.

Advantages of an adjustable floor on joists

Compared to leveling with concrete screed, adjustable joists offer the following advantages:

wet and dirty technical processes are excluded;
provided wide range floor lift levels from 5 to 15 cm and higher without any additional material and labor costs;
obtaining cost savings when raising the floor over 7 cm;
speed of the installation process (100 m2 in two days);
guarantee high precision alignment;
increased heat and sound insulation;
placement of all types of communications in the underground space, which makes it easier to access them during repair or replacement;
the lightness of the design, making it indispensable in houses where a large load on the floors is technologically unacceptable.

The following design options for adjustable joists are possible.

Installation of the floor on adjustable joists (video)

The main stages of installing an adjustable floor on joists

Preparatory work

The room in which it is planned to install adjustable joists is measured. Based on the measurements, the amount of timber for the logs with a margin for cutting, bolts for installation and dowel-nails for attaching them to concrete are calculated.
The level of the floor slab is checked and the final floor level is set taking into account the height of the flooring (plywood, OSB) and the height of the finishing coating.
In the logs with the required pitch, through holes are drilled with a feather drill, then, if you do not have threaded bushings, threads are cut into the holes with a tap. If you purchased ready-made plastic bushings, they are inserted into smooth holes and fastened to the joists with self-tapping screws.
The stand-up bolts are screwed into the holes of the joists using a hex key - the outer screws in each joist are screwed in completely, and the middle ones - to a small depth.

Important! If the surface of the floor slab under the post bolt is very uneven, it should be leveled with a chisel. The post bolts must be securely fastened to the concrete. Minimum distance there should be 10 mm between the floor slab and the joists.

Installation of logs

First, logs are installed along the perimeter of the room with a distance of 10-70 mm from the walls, the distance between the wall and the ends of the logs is 10-30 mm. When choosing the pitch between the logs, you should take into account the dimensions of the flooring sheets (slabs). The edges of the flooring slabs should rest on the joists and end near their central axes. The standard step size between the logs is 400-600 mm, however, to strengthen the structure, this step can be reduced to 300 mm. It is allowed to install cut-off joists supported by two stand-up bolts.
The outermost bolts in each lag are installed first. They are screwed into the joist to the required depth, controlling the preliminary position of the joist by level, after which all other stand-up bolts are lowered to the level of the slab.
After this, a thin drill is inserted into all the holes of the post-bolts and holes are marked in the concrete for the dowel-nails.
The lag is removed and the planned holes are drilled in the concrete. The joist is reinstalled, a dowel-nail is inserted into each bolt-post, which is lowered down the cone-shaped hole and falls exactly into the hole drilled in the concrete.
Next, lightly recess the dowel-nails in the 2 outer bolts-racks using a hammer. The log is set to the required height by rotating the two outer bolts with a hexagon, controlling the process by level.
The outer dowel-nails are finally driven into the concrete. Then screw the remaining stud bolts into the joists until they rest on the slab, recess and hammer the dowel nails into each stud bolt.

Using a chisel and a hammer, cut off the protruding ends of the bolts from the upper plane of the log. Check the rigidity of the fastening of the post bolts to the floor slab by pressing on each joist and trying to tear it off (lateral loosening is prohibited).

If any post bolt is not sufficiently fastened to the floor slab, it is unscrewed. Remove the dowel-nail and increase the depth of the hole in the concrete. The holes are cleared of dust and the post bolt is reattached.

If the required rigidity of fastening to the base is not achieved, then use other fasteners. For example, in the form of RDK - a nylon expansion dowel with a screw. The screws in the RDK dowels are tightened using a long bit with a screwdriver or drill. The screw must not be loosened or turned in the dowel thread.

Installation of the floor on adjustable joists (video)

Adjustable logs on metal studs

Let's consider how you can arrange adjustable logs from materials that can be purchased at any building materials store.

Regular steel studs can be used as adjustable supports for joists. The design of such adjustable lags on heels is as follows.

A typical dry planed timber with a cross section of 50x50 mm is used for the logs. Its adjustable support contains an M 6 pin, two nuts, two washers and an anchor sleeve.
IN concrete slab a hole is drilled into the ceiling, an anchor sleeve is driven into it against a spacer, into which a pin is screwed.
The lower (under the jog) nut with a washer is screwed onto the stud. A hole is drilled in the joist with a hammer on top.
The lag is put on the stud, so that the nut and washer are on its lower side. By rotating this nut you can adjust the position of the joist. The second nut (top) is necessary to fix the log at the set level.

As you can see, modern construction industry offers ever new alternatives to traditional construction technologies. Adjustable is a prime example of such an alternative, making it easier and cheaper to install and repair floors.

The new technology involves the use of wooden logs or slabs (sheets of moisture-resistant plywood), which are supported by stand-up bolts screwed into them, usually made of high-strength plastic. By rotating the bolts around their axis, the height of the joists or sheets changes, which allows you to accurately level the subfloor. After leveling the substructure, the bolt is firmly fixed to the base with a dowel-nail. Moreover, the base can be either concrete (monolithic, hollow, base with a screed) or wooden (beam). Sheets of moisture-resistant plywood are usually laid on top of the logs, and any type of floor covering is fixed on them - parquet, parquet boards, laminate, linoleum, carpet, etc. In order to save money solid boards sometimes they are mounted directly on the joists.

Adjustable joists

Possibility of leveling from 5 cm or more (at no additional cost)
No risk of flooding neighbors
Pleasantly warm floor
High sound insulation (necessary for home theaters)
Reduced costs for communications (all types of communications, including electricity, can be placed under the floor)
No dirty or wet work

Adjustable plates

Mechanical leveling method (without the risk of squeaking or shrinkage)
Cheaper than concrete
No dirty processes
Opportunity step-by-step assembly(if the apartment has furniture)
Cuts off completely impact noises that will disturb your neighbors
Assembly speed (from 20 m2 per day!)

Advantages of the system

Such adjustable structures have a number of advantages. First of all, they have advantages over concrete leveling. They are cheaper than a concrete screed if it is necessary to level a surface with a difference in height of more than 3-5 cm. In addition, they allow you to save money when installing a base for plank floor coverings (parquet, parquet boards, laminate), because concrete preparation in this case, it will include not only a screed, but also a self-leveling mixture (do not forget also about the need to create a plywood flooring on top of the screed, on which the plank floor will be laid).

In total, the costs of such preparation will be higher than the costs of installing an adjustable structure. No less important point: the concrete screed acquires the necessary strength within 28 days. While the installation of adjustable joists usually takes less than a week, since one worker installs an average of 20-25 m2 of adjustable joists or slabs per day. Moreover, according to VSN 9-94 “Instructions for installing floors in residential and public buildings", the moisture content of the screed should not exceed 5% to avoid deformation of the wooden floor. Note that European standards require drying the screed to 3-4%. It is a mistake to assume that it dries to this level in 28 days: this process takes longer than the curing process and usually takes several months. There is no direct contact in the design of adjustable supports wooden elements with the base of the floor, and therefore, you can lay logs on top of the concrete floor, and then you can lay plywood and parquet without waiting completely dry concrete. In the case of a ceiling with high humidity, you can lay a plastic film over it, thereby cutting off water vapor, and then immediately begin installing the joists or slabs. Finally, the adjustable design allows air to move under the floor and thereby remove excess water vapor that can lead to warping and rotting of the wood. The supply and exhaust of air is carried out due to the gaps between the floor and the wall of the room (on top it is closed with a plinth, but there is also a gap between it and the floor). The standard size of this gap is 10 mm. If you need to increase the ventilation of the space under the subfloor, you can install decorative grilles in the floor in opposite corners of the room for additional air supply and exhaust. Let us add that in regulated systems it is recommended to use only moisture-resistant plywood (grades no lower?) and logs made from chamber-dried timber with a humidity of no more than 12%.

Another advantage of adjustable structures is that they increase the sound insulation of the room: the floor is not monolithic, but contains in its “pie” air gap, which dampens noise. In addition, plastic racks prevent the spread of noise. If it is necessary to significantly increase the sound or heat insulation of the floor (for example, in a home theater or basement), you can lay slabs of wood between the joists. mineral wool. The slabs are laid on metal plates fixed to the joists. The thickness of the insulating layer can be varied, but there is usually no contact between the slabs and the concrete floor (there is only air gap), so in case high humidity the ceiling insulation will remain dry. Next moment: height-adjustable structures allow you to lay under flooring engineering communications (pipes with a diameter of more than 50 mm) and any wiring. Moreover, engineering communications will follow the shortest path, so there will be fewer connecting nodes, which means that the reliability of the system will be higher and the cost of its installation will be lower. One of the problems that arise when using a wooden floor is creaking. Is there a possibility of it appearing in floors along adjustable joists or slabs? Experts say that with high-quality installation of the system there will be no squeaking. It can occur when the floor elements do not fit tightly together, for example, when bolts are screwed incorrectly or the layers of plywood laid on top of the joists are poorly glued. However, with qualified installation, all elements of the system are so rigidly fixed to the base and interconnected that even a slight drying out of the wood, according to experts, will not result in a creaking floor. However, knocking noises in the floor may occur if concrete base, on which the logs rest, is made with errors: for example, if the screed applied to the ceiling crumbles or cracks. Then it is recommended to remove the bad screed before installing the floor, and also select the correct dowel-nail model for attaching the bolt to the base. Let us add that the maximum permissible load for adjustable structures - at least 3 tons per 1 m2. Their estimated service life is at least 50 years.

Installation of the structure

If it is necessary to raise the floor to a height of 5 cm or more, install a structure of adjustable joists. If the required lifting height is from 3 to 5 cm, then a system of adjustable slabs (plywood) is used. Let's start with the first option. When installing the floor on concrete floor Most often, logs with a cross section of 45x45 mm and a length of 2 or 3 m are used. Their standard pitch is 30 cm between the axes of the bars. When laying the floor on a ceiling made of wooden beams Usually, logs with a larger cross-section are required, the size of which is selected taking into account the pitch of the beams (as a rule, logs with a cross-section of 45x70 mm are used). You can also vary the lag pitch. For each joist there are 5 stand-up bolts for which threaded holes are prepared at the factory. The length of the bolts is usually 100 or 150 mm: it is chosen depending on the height to which the floor needs to be raised. The installation of the structure begins with screws being screwed into the logs, then the logs are laid out on the base with the required spacing, and holes for the dowel-nails are marked. Moreover, a gap of about 10 mm is left between the logs and the walls. Next, the bars are moved to the side, holes are drilled to a shallow depth, the bars are returned to their place and the dowels are driven through the bolts using a hammer and a punch into the prepared holes. Then they begin to level the joists by rotating the bolts with hex keys (the bolts have a hex groove), using a level. Having completed the alignment, the dowels are driven all the way into the base, and the protruding part of the plastic bolt is cut off flush with a chisel. Then the plywood flooring is installed. According to the recommendations of system manufacturers, the thickness of the flooring should be at least 18 mm. However, some parquet companies recommend installing solid boards and flooring up to 30 mm thick under the parquet with a lag pitch of 30 cm. Usually, two layers of sheets are laid (overlapping the junction of the two lower ones with the top sheet) to ensure maximum rigidity of the structure. As a rule, layers of plywood are fastened using self-tapping screws, however, when laying parquet, parquet companies also recommend gluing upper layer to the bottom. The flooring is installed on top of the plywood.

In the case of floors on adjustable slabs and on joists without ready-made threaded holes, the installation technology is somewhat different. A hole is drilled in the plywood or joist into which a plastic sleeve with a threaded hole is inserted. The sleeve is secured to the joist or plywood with self-tapping screws. Then the post bolt is screwed into the bushing, after which the entire cycle of the work listed above is performed.
Let us add that there are other adjustable designs on the market. In particular, systems where metal stand-up bolts are used, and adjustment occurs using a nut screwed onto them with a support washer. There are also systems with U-shaped metal brackets, which “grab” the lag from the sides and are secured to it with self-tapping screws. The bracket provides whole line holes, and after alignment, screws are screwed into holes of suitable height.

“Adjustable floors on joists or on plywood boards have obvious advantages above the concrete alignment, if we are not talking about abstract “ concrete screed", but about the base for parquet, parquet boards or laminate, which includes a layer of screed, a layer of self-leveling mixture and a layer of plywood. Adjustable structures are cheaper than such a base, especially when it is necessary to level a floor with large differences in height. In addition, a concrete screed gains strength within 28 days, while installation of an adjustable floor usually takes from 2-3 days to a week. In addition, utilities and wiring can be laid under the adjustable floor, and, if necessary, heat and sound insulation slabs. However, such a floor itself increases the sound insulation of the room due to the air “cushion” between the floor covering and the ceiling, as well as through the use of plastic bolts.

Technology comparison

Characteristics	Adjustable floor under the board	Adjustable floor for any finishing coating, including joists + plywood for parquet)	Raised floor	Rough concrete screed (primer, waterproofing, screed)	Finish concrete preparation for parquet coverings ( rough screed, leveling screed, FC plywood)	Dry screed KNAUF
Installation time 30 sq.m., day	1	1	1	21- 28	from 31	1
Cost of material with work per m2	from 1200 rub.	from 1350 rub.	from 1450 rub.	from 700 rub.	from 1200 rub.	from 1150 rub.
Difference of floor base*	Resp. SNiP	Resp. SNiP	Resp. SNiP	Resp. SNiP	Resp. SNiP	Resp. SNiP
less than 19	19-20	from 38	from 70	from 80	from 40
Increased sound-heat insulation	+	+	+	-	-	+
Possibility of placing utilities in underground space	+	+	+	-	-	+
Load-bearing capacity, kg per sq.m.	from 3000	from 3000	from 1000	from 3000	from 3000 kg	from 1000
Application area	All types of premises	All types of premises	Comm. wk.	All types of premises	All types of premises	All types of premises
Permissible floor lift height, cm	3-30	3-30	5-150	3-15	3-15	5-15
Application in damp areas	Dry rooms	Dry rooms	Dry rooms	Dry rooms	Dry rooms	Dry rooms
Prev. floor preparation	not required	not required	required	required	required	required
Types of floors for installation	Any	Any	Monolith. blocked	Monolith. blocked	Monolith. blocked	Monolith. blocked

Adjustable floor - subfloor in the form of joists or plywood flooring

As a rule, flooring in residential premises is laid on a concrete screed and joists. A relatively new option is subfloor construction in the form of logs or plywood flooring, the height of which can be adjusted using special rack blocks. This solution received a quite understandable name - adjustable floor.

Adjustable floor technology involves the use of wooden logs or slabs (sheets of 18 mm moisture-resistant plywood), which are supported by stand-up bolts screwed into them, usually made of high-strength plastic. Turning the bolts around an axis changes the height of the joists or sheets, which allows you to accurately level the subfloor. After leveling the structure, the bolt is rigidly fixed to the base with a dowel-nail. In this case, the base can be either concrete (monolithic, hollow, with a screed) or wooden (beam). Sheets of moisture-resistant plywood are usually laid on top of the logs and any type of floor covering is fixed on them - solid boards, parquet, parquet boards, laminate, linoleum, carpet, etc. In order to save money, massive boards are sometimes mounted directly on the logs.

Advantages of an adjustable floor system

Such adjustable structures have a number of advantages. First of all, they have advantages over concrete leveling.

They cost less than concrete screed when leveling a surface with a height difference of more than 3-5 cm.
There is no need to fuss with cement.
Installation of adjustable floors be produced much faster pouring concrete screed.

In addition, they allow you to save money and time when laying the base for plank floor coverings (parquet, parquet boards, laminate), because the concrete preparation in this case will include not only a screed, but also a self-leveling mixture.

Do not forget also about the need to create waterproofing (and often sound insulation) on top of the screed and a layer of plywood on which it will be laid wood covering. In total, the costs of such preparation will be higher than the costs of installing an adjustable structure.

Another important point: installation of adjustable joists usually takes less than a week, since one worker installs an average of 20-25 m² of adjustable joists or slabs per day. The situation is completely different with a base made of concrete screed: to carry out parquet work, its strength must be at least 150 kg/cm², and the screed acquires such strength within 28 days. However, this time period is not enough to start laying parquet or boards.

Note that European standards require drying the screed to 3-4%. It is a mistake to assume that it dries to this level in 28 days: this process takes longer than the curing process and usually takes several months.

In the design of adjustable supports, there is no direct contact of wooden elements with the base of the floor, and, therefore, it is possible to lay logs on top of the concrete floor, and then plywood and parquet, without waiting for the concrete to completely dry. In case of overlapping with high humidity, lay on it plastic film, cutting off water vapor, after which the installation of logs or slabs immediately begins.

Finally, the adjustable floor design offers the possibility air movement under the floor and thereby removing excess water vapor, which can lead to warping and rotting of wood. The supply and exhaust of air is carried out due to the gaps between the floor and the wall of the room (there is also a gap between the baseboard fixed to the wall and the floor). The standard value of this gap is 10 mm. If you need to improve the ventilation of the space under the subfloor, you can install decorative grilles in the floor in opposite corners of the room for additional air supply and exhaust.

Another advantage of adjustable structures is that they improve sound insulation of the room: the floor is not monolithic, but contains an air layer in its “pie”. If necessary, increase the level of sound or heat insulation of the floor (for example, in a home theater or ground floor) you can lay mineral wool slabs between the joists. In addition, plastic racks dampen the noise.

Adjustable floor slabs are laid on metal plates fixed to joists. The thickness of the insulating layer can be varied, but there is usually no contact between the slabs and the concrete base (they are separated by an air gap), so that in case of increased humidity of the floor, the insulation will remain dry.

Next point: height-adjustable floors allow the installation of utility lines under the floor covering(pipes with a diameter of up to 100 mm) and any wiring. Moreover, communications will take the shortest path, so there will be fewer connecting nodes, therefore, the reliability of the system will increase, and the cost of its installation, on the contrary, will decrease.

Adjustable floors on joists or on plywood slabs have obvious advantages over concrete leveling if we're talking about not about an abstract “concrete screed”, but about the base for parquet, parquet boards or laminate, which includes layer, layer and layer. Adjustable structures are cheaper than such a base, especially when it is necessary to level a floor with large differences in height.

In addition, it gains strength within 28 days, while installation of an adjustable floor usually takes from 2-3 days to a week. In addition, utilities and wiring can be laid under the adjustable floor, and, if necessary, heat and sound insulation slabs. However, such a floor itself increases the sound insulation of the room due to air cushion between the floor covering and the ceiling, as well as through the use of plastic post bolts.

Problems and disadvantages of adjustable floors

One of the problems that arise when using a wooden floor is creak. Is there a possibility of it appearing in floors along adjustable joists or slabs? Experts say that with high-quality installation of the system there will be no squeaking. It can occur when the floor elements do not adhere tightly to each other, for example, when bolts are incorrectly fastened to the base or the gaps are incorrectly formed between the end joints of the joists and plywood. However, with qualified installation, all elements of the system are so rigidly fixed to the base and interconnected that even a slight drying of the wood, according to experts, will not result in a creaking floor.

However, There may be a knock on the floor, if the concrete base on which the logs rest is made with errors: for example, if the screed applied to the ceiling crumbles or cracks. Then it is recommended to remove the bad screed before installing the floor, and also select the correct dowel-nail model for attaching the bolt to the base.

Poor cleaning of dust when installing adjustable structures leads to dust particles getting into the gaps, which can lead to creaking in the floor.

Let us add that the maximum permissible pressure on adjustable structures can reach 3 tons per 1 m², which corresponds to a large safety margin for the floor. Their estimated service life is at least 50 years.

Another possible (not everyone even notices it) disadvantages of adjustable floors can be called a kind of hum when moving along them, especially if the shoes have high heels or the soles are very hard. This is especially evident if you jump on such a floor.

Installation of adjustable floors

If it is necessary to raise the floor by 50 mm or more, install adjustable joist design. And if the required lifting height is from 30 to 50 mm, use system of adjustable boards (plywood).

Adjustable joist system (adjustable floor on joists).

When installing a floor on a concrete floor, logs with a cross section of 45 x 45 mm and a length of 2 or 3 m are most often used. Their standard pitch is 300 mm between the axes of the bars. When laying a floor on a floor made of wooden beams, logs of a larger cross-section are usually required; its size is selected taking into account the pitch of the beams (as a rule, logs with a cross-section of 45 x 70 mm are used). You can also vary the lag pitch. For each lag there are 5 stand-up bolts with a diameter of 28 mm, for which threaded holes are prepared at the factory.

The length of the bolts is usually 100 or 150 mm: it is chosen depending on the height to which the floor needs to be raised. The installation of the structure begins with bolts being screwed into the logs, then the logs are laid out on the base with the required pitch and holes for dowel-nails are marked. Moreover, a gap of about 10 mm is left between the logs and the walls.

First, bolts are screwed into the logs, after which they are laid out on the base, marking and then drilling holes for dowel-nails

Alignment of the lags is carried out using a level and a hex wrench

Then they begin to level the joists by rotating the bolts with a hex wrench (the bolts have a hex groove), using a level.

The height of the plastic bolts is adjusted using a special hex key

Having completed the alignment, the dowels are driven all the way into the base, and the protruding part of the plastic bolt is cut off flush with a chisel.

After leveling the joists, the dowels are driven all the way into the base

Then the plywood flooring is installed. According to the recommendations of system manufacturers, the thickness of the flooring should be at least 18 mm. However, many experts recommend making flooring up to 30 mm thick with a lag pitch of 300 mm under parquet and solid boards.

As a rule, two layers of plywood sheets are laid (with the top sheet overlapping the junction of the two lower ones) to ensure maximum structural rigidity. As a rule, layers of plywood are fastened with self-tapping screws, but experts increasingly recommend that in addition to this, be sure to glue the top layer to the bottom. The flooring is installed on top of the plywood.

Let us add that there are other adjustable designs on the market. In particular, systems where metal stand-up bolts (anchors) are used, and adjustment occurs using a nut screwed onto them with a support washer.

There are also systems with U-shaped metal brackets that “clasp” the lag from the sides and are secured to it with self-tapping screws. The bracket is provided with a number of holes, and after alignment, the screws are screwed into holes of suitable height.

The reliability of the floor structure with adjustable joists is achieved due to the right choice section and pitch of the lag in combination with the thickness of the subfloor, as well as due to high-quality installation. In a standard situation, the pitch of a lag with a section of 45 x 45 mm should be 300 mm with a subfloor thickness of 30 mm (usually two layers of plywood with sheet thicknesses of 18 and 12 mm). Layers of plywood should be glued together to achieve maximum structural rigidity.

There is an exception: if you use parquet board fixed to the base with glue, it is enough to lay one layer of 18 mm plywood, since such a board and plywood have the same amount of thermal expansion, and the rigidity of the structure is beyond doubt. The cross-section and pitch of the joists change, as a rule, when the floor is laid on top of a floor made of wooden beams. The distance between the beams can be quite large (1 m or more), so you have to either increase the section of the logs, or install the logs with a smaller pitch and increase the thickness of the two-layer flooring - made of plywood or a combination of tongue-and-groove boards and plywood.

The price of components for adjustable floor structures starts from 400 rubles/m². Adjustable plywood floor installation kit

Adjustable slab system (adjustable plywood floor).

The technology for installing an adjustable plywood floor is somewhat different. A hole is drilled in the plywood into which a plastic sleeve with a diameter of 60 mm, having a threaded hole, is inserted. The sleeve is secured to the joist or plywood with self-tapping screws. Then the post bolt is screwed into the bushing, after which the entire cycle of the work listed above is performed.

Technology for constructing a system of adjustable slabs (plywood):

	1. Drilling holes in plywood and fixing plastic bushings with self-tapping screws;
	2. Screwing the post bolts into the bushings
	3. Fastening the stand-bolts with metal dowel-nails to the base