What to put under the joists on a concrete floor?

Residential property owners are sometimes faced with the need to replace outdated flooring. This kind of problem cannot be solved immediately. It is associated with a significant waste of financial resources and the issue of selecting the type of ceiling.

There are several types of foundation: screed

, reinforced concrete floor slabs or floors on wooden blocks, which are distinguished by their raw material base, installation method, and properties.
To install: a screed
or a transverse beam - which is better and more convenient, you need to consider any option separately, find out its advantages and only then make a selection.

Base floor diagram

Attaching joists to a concrete floor: section answers to readers' questions

Hello again and thank you very much for your detailed answer regarding puttying cracks in concrete. I have done this work, now I am starting to insulate the floor. And again I had a question: is it necessary to attach the joists to the concrete floor or can I just assemble the lattice and fasten it with rough flooring? In my case it's plywood.

If necessary, how is this done correctly, and what fasteners are best to use?

Hello, Ivan. We are glad that we helped you, we will try to help you again.

Let's see what consequences can result from a reluctance to follow technology when installing a floor along joists on a concrete base.

Methods for installing joists on a concrete floor

Installation work consists of laying wooden beams on prefabricated or monolithic reinforced concrete foundations.

An important condition for high-quality performance of work is the correct choice of fasteners and compliance with the technological scheme for placing logs on the base surface:

The beam should be installed across the line of light from the windows, parallel to the window or doorway. It is necessary to leave a gap of 25-30 mm wide between the walls and the profile.
If sound insulation is needed, then the substrate under the logs is laid in a continuous strip along the entire length, without breaks.
Mounting holes and seams between prefabricated elements must be filled with cement-sand mortar of a grade not lower than M150.
The joists must touch the surface of the floor slabs without gaps. It is recommended to fill the voids between the timber and the base with fine sand or fill them with polyurethane foam.
The minimum length of the bars to be joined must be ≥ 2 m. Short profiles should be joined together with their ends facing each other anywhere in the room with the seams in parallel joists offset by 0.5 m.
In the doorways of adjacent rooms, it is necessary to place a widened beam protruding beyond the partition by 50 mm on both sides. This is done so that the finishing coating in different rooms rests on the same base.
The horizontal level of laying profiles is checked with a two-meter rack tool.
Before installing the finishing flooring, the space under the floor is cleared of wood chips, shavings and debris.

Self-tapping screws

Through holes are drilled in the joists 0.5-1.5 mm smaller than the diameter of the screw. Holes for plugs are drilled in the floor slab using a hammer drill. Then a nylon dowel is inserted into the concrete floor and the profile is laid. Check the alignment of the holes and screw in the screw. The horizontal level of the logs is adjusted using fasteners and substrates, loosening or tightening the connection.

Fastening with anchors

Anchors provide a stronger connection than dowels or screws. The principle of installing devices is the same as for self-tapping screws, but instead of a nylon dowel, a metal spacer sleeve is inserted into the base. The optimal fastener diameter is 6-10 mm, length is 50-150 mm. Due to the high connection density, one anchor is enough per 1 m of timber.

Fastening the log to a metal corner

The profile is attached on either side to the base of the floor using a dowel or anchor. The lag is placed in the cavity of the corner and screwed in place. The distance between the fasteners depends on the length of the room and should be 35-50 mm.

The same procedure can be done using metal perforated brackets. In this case, the beam will be covered on both sides by the shelves of the device.

Adjustable joists

Adjustable fasteners for the subfloor can be of 4 types:

plastic supports (posts);
studs with nut and washer;
polymer bolt-stand;
threaded bushings.

The most convenient are factory-made designs with through threaded couplings, which can be of the following sizes:

0.45 x 0.45 x 2.0 m;
0.45 x 0.70 x 2.0 m;
0.45 x 120 x 2.0 m.

They are supplied with threaded posts for adjusting the profile rise level and dowels for attaching post bolts to the base.

Before installing the structure, plastic post bolts are screwed into the holes in the profile, on which the logs will rest.
The bars must be placed parallel to each other in increments of 350-375 mm.
Then holes are drilled in the concrete base for installation of vertical connections. A dowel-nail is placed in this place through the stand.
Using a special key, turning the mounting post left and right, adjust the horizontal level of the log.
Drive the dowel-nail all the way, check the reliability of the connection and move on to the next profile.

Attaching joists to concrete pillars

Under the logs installed on concrete pillars, 1-2 layers of waterproofing material (roofing material, etc.) are laid, the edges of which should extend beyond the boundaries of the base by 30-40 mm. A fiberboard substrate is placed on top of the insulation in one layer. The profiles are fastened using dowels or self-tapping screws.

Installation process

It’s worth clarifying right away that using floor joists is only advisable in apartments with high ceilings. This floor installation technology “steals” the height of the premises quite significantly. So, the installation of the logs occurs according to the following scheme:

It is recommended to level the screed or concrete base. Otherwise, the elements will not be in the same horizontal plane. Accordingly, they will need to be leveled by placing plates. This can lead to the floors in the apartment creaking.
You need to lay a layer of waterproofing on the base, or treat the concrete with a special mastic. In the first case, the use of soft materials should be avoided. Over time, they will sag, and the floor will no longer be reliable and solid. For a waterproofing layer, roofing felt or polyethylene film is perfect.
The logs are treated with an antiseptic compound and cut according to the size of the room.
The installation process begins with installing joists at two opposite walls. These elements are leveled using a building level and immediately fixed to the concrete floor. Then a string is stretched between the installed joists. It will serve as a guide for the installation of other elements.

The remaining logs are laid. The distance between the elements directly depends on the thickness of the future floor covering.
Insulation is poured between the joists. For this, ecowool or rolled materials can be used. In the second case, you need to mount the material as tightly as possible without leaving gaps between the layers.
A layer of vapor barrier is laid down. This is a necessary condition for protecting the insulation from external influences. The vapor barrier can be attached using a stapler; the joints must be taped.
You can lay a layer of plywood. This will serve as the basis for installing the flooring.

Application area

It’s not enough to know how to level a floor without a screed. The design features of each individual type influence the scope of application in everyday life.

Server rooms and transformer stations.
Leveling the floor without a screed allows you to place utilities, pipes, wiring, etc. inside (under the floor).
For further finishing leveling. It takes minimal time, and the result will be interesting to everyone.
New houses require attention from new residents. First of all, this concerns the floors. They are not always brought to average levels. Consequently, they have to be leveled, and most often without pouring the solution.
Installation of multi-level floors.
Reconstruction of old buildings.
Raising the floor level without additional load.

That is, the scope of application is very wide. In addition to houses and apartments, they are becoming popular in educational institutions, conference rooms, industrial premises, etc.

Installing a floor on the ground

Installing floors on joists is not as difficult as it might seem at first glance. They have a simple design; they can be made for an apartment, private house, or country cottage. Unlike concrete pouring, the weight of such a structure is less, but the floor is in no way inferior in strength.

To install logs, you need to follow fairly simple instructions:

Scheme of a wooden floor on joists on the ground

First, the soil base is inspected, after which the soil is thoroughly compacted with a vibrator. If there is no such equipment, then the work can be done with a piece of large diameter log.
A layer of crushed stone is then poured onto the ground; it should be approximately 5 cm. This layer will serve as the base.
After this, it is necessary to construct the formwork for each support separately. A preliminary diagram of the location of supports is drawn up in accordance with the size of the room and the conditions of construction of the entire structure. If the formwork is ready, then pouring can be done.
Next you need to build brick supports. In this case, a layer of waterproofing must be provided between the supports themselves and the base. This will reliably protect the structure from moisture. Another layer of waterproofing should be done over the brick support and a soundproofing gasket should be installed.
Next, floor joists are installed. The boards are pre-cut into pieces of the required size, and then their surface is treated with an antiseptic and fire retardant. This will protect them from damage by insects, from mold, and make them more protected from fires.
The logs are fixed to the supports with special dowels, which ensure reliability and stability. After this, you can lay a special cranial block, make a primary plank flooring, you can use ordinary boards for it. After rolling, you can lay out another layer of waterproofing material.
A heat insulator must be installed between the joists. Various materials can be used in this capacity. Manufacturers offer a wide variety of insulation materials suitable specifically for floors on joists. In this case, you can take expanded clay, other bulk materials, foam boards, mineral wool boards.
During insulation, it is necessary to ensure that no air layers or cavities remain, as this will negatively affect the condition of the thermal insulation and heat loss will be observed.
After this, it is necessary to level the floor joists. The upper horizontal level is determined. All excess is cut off, and the horizontalness of the coating is checked with a building level.
The finished floor is mounted from sheets of plywood or chipboard; any floor finishing materials can be laid on them. During installation, you will have to ensure that there is a temperature gap of 2 mm between the slabs, and 10 mm between the slabs and the wall. For strength, plywood can be laid in 2 layers, the total thickness of the sheathing is from 12 mm to 20 mm, it all depends on the requirements for the floor. It is necessary to leave a small ventilation gap between the sheathing and the insulation.
After the floor covering is completed, it is necessary to once again check the horizontalness of the floor, and then sand the surface. To avoid damaging the sander, the heads of the screws should be sunk into the wood during fastening. The last step is laying the flooring. The process depends entirely on what material was chosen for the job.

Attaching the joists to the concrete floor yourself. To fasten or not to fasten?

Opponents of fastening argue that such a procedure can destroy the screed; moreover, at the junction of the joists and the base, sound insulation is disrupted and so-called sound transmission bridges arise, and the neighbors below will definitely not like this. But supporters of rigid fixation cite examples from their practice when the deformation of wooden beams negated all efforts to repair the floor.

How is it really going? As for destroying the screed, doing this with a drill by drilling holes in the concrete will not work if the screed is strong enough. A solid foundation is one of the prerequisites, without which they cannot begin to repair the floor. The old screed, if it has already begun to fall apart, must be removed.

Removing old screed

Regarding the violation of sound insulation, the issue is controversial. Yes, indeed, rigid structures are capable of transmitting sound, but is everything so bad? A layer of insulation is placed in the cells between the joists, which has soundproofing properties.

A layer of insulation is placed in the cells between the joists

A shock-absorbing pad is placed under the joist supports, which also prevents the propagation of sound waves. The sound transmission bridge formed at the fastening site transmits vibrations into concrete, and this material is quite dense and does not conduct sound as well as, for example, wood. Therefore, the neighbors below are unlikely to notice the difference in noise levels before and after the renovation.

A floor on joists is a structure consisting of many elements: beams, fastening devices, rough flooring. All these parts, moving relative to each other, will emit a constant squeak, which is much worse and will no longer please the neighbors. One way to avoid unpleasant squeaking is to firmly attach the joists to the floor.

Floor on joists construction

Another argument in favor of fastening is fixing the lag. It is impossible to check the degree of drying of the wood by eye, so you have to trust the seller. Insufficiently dry beams can bend and twist after some time, and this will lead to shifts in the coating, so that the entire complex device will be skewed.

Those who are still wary can opt for a traditional floating floor, that is, a system in which the flooring does not have a rigid connection with the supporting structures. This guarantees excellent sound insulation, but requires well-dried logs that will definitely not fade over time.

Floor installation using adjustable joists

The rigidity of the floating floor is provided by beams securely fastened to each other, forming a lattice. Insulation is placed in its cells, and a rough flooring is attached on top, so that the entire structure will be pressed to the floor by its own weight. If everything is done correctly, then such a floor will not deform over time and will last a long time.

However, most often the joists are still attached to the floor: there are more positive aspects than possible disadvantages.

Work order

How to lay floor joists with your own hands

The main thing on which the success of the renovation will depend is quality materials. Coniferous wood with a moisture content of no more than 18% is suitable for logs. The purchased beams need to be brought home and allowed to lie in the room for several days so that the material gets used to the microclimate of the room. Those logs that began to bend in the heat should be discarded. By the way, all wooden elements of the future floor must be treated with an antiseptic so that they do not become moldy and insects do not infest them. Treatment with special compounds that reduce flammability will also be required.

Coniferous wood is suitable for logs

Installation, fastening and alignment of joists

Now that the joist system is completely ready, all that remains is to attach them to the floor. The actual fastening is carried out in three ways: dowels + self-tapping screws, anchor fastenings and galvanized corners with self-tapping screws. Which one to choose is a matter of budget and personal preferences of the developer, since each method has its own characteristics.

Video - How to lay joists

Fastening the joists with self-tapping screws

Perhaps the simplest and cheapest option that allows you to achieve excellent results. Through holes are drilled in the beams, and symmetrical ones are made through them at the base. A plastic dowel is inserted there and a self-tapping screw is screwed in. Step – 40-80 cm depending on the situation.

The length of the screw depends on the thickness of the timber and should allow it to go 5-6 cm into the base. By the way, some craftsmen recommend self-tapping screws with a neck, that is, those in which the thread does not reach the head. This will allow the joist to be better pulled to the floor.

Fastening joists with anchors

Anchors guarantee reliability and durability of fastening. Their main advantage in this case is that they not only hold the beam in place, but also attract it to the floor, giving the structure additional rigidity.

Essentially, an anchor is the same dowel, but more powerful. Its advantage is resistance to tearing, so it is used when installing heavy structures that create a high load on the fasteners. A floor laid on joists will most likely not have situations where its entire complex structure will be completely torn away from the concrete surface, so you can limit yourself to self-tapping screws, but the use of anchors is a very common practice.

Fastening is carried out in the same way as in the previous case. Holes are drilled in the joists, which are then duplicated on the concrete base. The joists additionally need to be countersinked to hide the bolt head without damaging the wood.

As a rule, on a room scale, 3-4 anchors are enough to secure one joist. The locking part of the anchor is inserted into the holes in the floor, and the bolt itself is screwed into it through the beam.

The length of anchor bolts can be very different, from 45 to 200 mm. You need to buy those that will be buried in the base, stitching through the lag, by 6 cm. The recommended diameter is 10 mm.

Fastening joists with corners

Galvanized metal angles are another option for attaching wood beams to a concrete floor. To do this, one side of the corner is connected to the beam by screwing a self-tapping screw into the wood. The depth is 3-4 cm, and it is recommended to do it at an angle to increase strength.

The remaining side of the corner should rest on the floor. It is fixed on this base using the methods already described above: with dowels or anchors. As an option, you can use not corners, but a U-shaped profile.

Attaching adjustable joists

An adjustable system costs more, but is easier to use and will make it easier to achieve horizontality. Here, instead of anchors, plastic posts are used, screwed into wood and attached to the base with dowels. The height can be adjusted by rotating special bolts, the protruding part of which is cut off after the adjustment is completed.

Attaching adjustable joists

So, you will have to decide for yourself whether to attach the logs to the floor or not. This definitely should not be done in wooden houses, but as for rooms with a concrete base, fastening will not hurt. The technology is simple and accessible to everyone; the main thing in such work is to choose high-quality materials and strictly follow all the rules. Then none of the structural elements will become loose over time, and the floor on the joists will be reliable and durable.

How to determine the condition of a wooden floor in a house

Even before taking any action, you need to get a complete picture of the condition of the floor. At least in order to understand whether it is necessary and whether it is rational at all to level it at this stage. Maybe it’s easier to completely dismantle it and go a different route?

In a word, the plank flooring requires revision.

To do this, the surface is cleared of debris and the condition of the boards is analyzed. First of all, visually. Definitely need to be replaced - rotten, broken floorboards. There are also boards damaged by insects. Woodworms very quickly spoil the structure of the tree, turning it into dust, and such boards can no longer be saved.

You need to “walk” across all surfaces of the plank floor, with an accentuated load on certain areas. This will allow you to identify areas of instability (unacceptably strong deflection) and areas where squeaks appear. All this should also be eliminated as it is identified. Presumably, there will be no one willing to leave the squeaky floor and simply cover it with a new covering.

Most likely, boards that have “begun” will be identified, that is, they have developed spatial deformation over time. But at the same time, by the way, remain strong, not affected by any nasty things. If it is clear that its curvature can be corrected, say, by scraping, then it is permissible to leave it as is for now. But if the board begins to deteriorate, only replace it with a new one.

Before starting leveling work, the floor should be subjected to a very thorough inspection and, if necessary, repaired.

By the way, it is possible and necessary to determine the condition of the boards not only visually, but also by sound. To do this, in suspicious areas, the floors are tapped with a wooden mallet. If the sound is clear, then everything is fine with the board so far. If the echo is dull, then the board is most likely already affected by biological decomposition and requires immediate replacement.

During the inspection, you should also pay attention to the nails. Sticking out, dangling, bent - must be immediately removed and replaced with new ones.

The worst thing is if there is nowhere to drive these same nails - that is, they simply do not hold after entering the joists. This is already a signal about the unsatisfactory condition of the logs themselves. If they are rotten, have lost stability, and are unable to bear the load, then nothing will definitely come of our venture. And that means you will have to remove all the boards to get to the joists in order to dismantle and replace them. That is, in fact, it is necessary to re-cover the entire floor.

However, let us return to those cases when leveling without dismantling is considered possible. What methods can be used then?

Preparing the base

The easiest way to lay logs on a concrete base is if it is perfectly level. Therefore, before installing them, it is better to fill the base with a leveling screed. Similar work has to be carried out on an existing concrete floor: it often needs repair.

To make a concrete floor suitable for laying beams, it is necessary:

remove the old coating from it;
remove peeling screed fragments, dirt, debris, mold from the ceiling;
dry the base thoroughly;
soak it with an antiseptic composition;
After the antiseptic has dried, treat the floors with a primer;
plaster the cracks and deep depressions in the base.

When the solution hardens, waterproofing is placed on the concrete - dense polyethylene or rolled bitumen material. Bitumen-based mastics are often used as a waterproofing agent. They coat not only the concrete floor, but also the walls in the lower part. Also, film, roofing felt, etc. are placed on them with an overlap. The height of the overlap depends on the thickness of the screed that is to be poured.

Without special devices for determining the plane, it will be difficult to obtain a flat concrete base for the logs. To achieve a high-quality result, you will have to use the following materials and tools:

chalk;
hydraulic level;
roulette;
painting cord;
synthetic thread;
gypsum;
beacons;
rule.

You will also need an impact drill, a screwdriver, and dowel nails.

On any wall of the room at a height of 1-1.2 m you need to put a chalk mark. On the same horizontal line as the first point, 2-3 marks should be made on all walls of the room. On each of them, between the marks, you need to beat off the lines with a paint cord rubbed with chalk.

The highest protrusion is determined from the base. A mark is placed on the wall at the level of the highest point of the floor. Another one is applied 2-3 cm higher. The distance is measured between the last mark and the previously marked line. Based on the measurement results, other marks are made on the walls, which are also connected by a horizontal line. Dowel-nails are inserted into the walls along it. Threads are pulled between opposite walls.

The screed plane has been built. Using the threads on the base as a guide, you need to place the beacon profiles. They are fixed to the floor with plaster. When it hardens, you can pour the screed. Align it with the rule.

What is a screed

You can level the floor base using one of the following methods: screed or wooden joists. The screed happens:

Wet.
Dry.

These are different technological processes. Wet technology involves the production of cement mortar using water . The finished mixture is poured onto the work surface, then leveled. Advantages of this coating:

They hide communications, a pipeline crossing the floor.
Distributes thermal insulation loads.
Adjust slopes.

In addition, the basis is obtained:

Neat.
Smooth.
Durable.

The developer will have to take into account:

Prepare the base with careful leveling.
Working moments with installing beacons, mixing the solution in the required portions of each component.
The adjacent surfaces of the house will receive their share of moisture from the cement screed.
You have to wait until the coating is completely dry; usually the solution hardens for a month.
For a specific period, movement in this area is excluded, which creates inconvenience and disorder in other rooms from construction dust.
Finishing in the room stops until the solution has completely hardened.
After the mixture hardens, an undesirable result may result from uneven settlements; you will have to use materials with self-leveling properties.
The complexity of the technological process, which is carried out according to certain rules, calculations of area and quantity of materials with the selection of tools.

For dry screed, finely dispersed expanded clay . This bulk material is evenly distributed and leveled as a rule over the floor surface of the room. The finishing coating can be immediately laid on such a base. But no master can give a guarantee that during operation deformation will not begin to appear in areas of greatest load.

Which tree to choose?

Types of materials

An important point in installing wooden floors is the choice of wood. For these works, the building materials market offers the following types of building materials for the consumer to choose from:

Six-meter boards can be used as covering material.

Six meter boards. The thickness of the products ranges from 20 to 60 mm. Using grooves and tongues at the edges, the wood is joined.
Two-meter parquet. These products are not only shorter in length, but also thinner. It is 18-25 mm. The joining principle is similar to the previous type.
Engineering. They are products glued together from three layers of wood. Pine is used for the lower part, and the upper parts are made of valuable wood.

Criterias of choice

Wooden boards are used for both rough and finishing installation. If the wood flooring is planned to be covered with laminate or linoleum, then the quality of the material can be chosen even unplaned. If the wooden covering on the concrete base is the finishing one, then the boards chosen are tongue-and-groove with a planed surface. When choosing wood, the following criteria are adhered to:

To perform such work, the material must be carefully sanded.

The wood must be dried, but not overdried, since excessive dryness leads to deformation of the boards under the influence of moisture and temperature changes.
The material is purchased with a margin of 15%.
The boards must be smooth, sanded and free from defects.
Wood from different batches may differ in shade and texture, so experienced experts recommend buying boards of the same type.
Regardless of the quality of the wood, the boards must be at least 2 m long.
When installing flooring on a concrete base, raw materials made from softwood are most often chosen, as they are resistant to abrasion. Material made from oak and beech is more durable and expensive.

Selecting the thickness of the material for leveling

Another parameter of sheet materials that needs to be taken into account when selecting is their thickness. Factors that influence the choice of material thickness:

type of base for installation;
type of finishing coating;
planned load on the floor.

The thickness of plywood for a wooden floor with slight “waviness” should be at least 8-10 mm. If parquet or laminate is to be laid as a finished floor, it is worth increasing the thickness to 10-16 mm. For carpet and linoleum, the thickness is increased to 16-18 mm. Installation of heavy furniture or equipment in an apartment or house will require a thickness of up to 21 mm.

Installation on plywood base

Laying a wooden floor on a concrete screed can be done using moisture-resistant plywood, the thickness of which ranges from 12 to 18 mm. How it's done?

Plywood is cut into squares 40x40 or 80x80 cm.
Plywood sheets undergo rough sanding.
The sheets are spread at intervals of 4 mm diagonally towards the future wooden floor. First, the plywood is fixed with glue, and then with dowels. It is necessary to retreat 10 mm from the wall. Laying plywood sheets is similar to laying bricks. The screw heads are recessed by 3-4 mm.
The surface is cleaned of dust and dirt.
The floorboards are attached with self-tapping screws to the plywood.

Laying wooden floors on a concrete screed is not difficult. If the installation technology is followed, such floors will last for many years and will provide warmth and a comfortable microclimate in the house.

Dear reader, leave your opinion on the article in the comments and share your secrets of installing wooden floors.

Location rules

The first and last lags from the wall should be at a distance of no more than 20 cm. If, while observing the calculated step, the outermost lags are located further, their number is increased and the step is reduced.

They are placed either along the wall in which the door is located, or perpendicular to it. If one wall is much longer than the other, then it is along this long wall that the logs are placed. If the room is square or similar in shape, then the location of the window may influence the choice: floorboards look best if they are located along the flow of light. That is, in this case, the logs are placed along the wall in which there is a window.