Selecting fasteners and attaching wooden joists to a concrete floor

Wooden logs are essential to ensure natural ventilation of the underground space and better heat retention in the premises. Thanks to the use of logs, the floor covering can last much longer. However, among people who do not have much experience in construction, you can often hear the question: is it necessary to attach joists to a concrete floor? Experienced craftsmen know that for a truly durable flooring that does not change its geometry under load, and for its long service life, it is imperative to correctly fix the logs on any supporting structure, including on a concrete screed.

Now that it is clear whether it is necessary to attach the joists to the concrete floor, it is worth noting that this task is not difficult, does not require special skills and knowledge, and, therefore, can be done by any home craftsman.

Technical features

Installing a floor on joists on top of a concrete base is a common solution. However, it comes with the potential for three common problems. These include:

• destruction of the monolith due to the use of many fasteners;
• deterioration of the situation with sound insulation of the floor due to the appearance of sound bridges in places where hardware is immersed in a dense structure;
• the appearance of squeaking due to friction of wood fibers on metal, which is inevitable if installation is carried out without following the rules.

All this can be avoided. So, if a concrete screed collapses, it means it was made with violations of the technological process or is of low quality. It is recommended to dismantle this coating and replace it with new material. A properly prepared solution, after hardening, retains its characteristics after drilling holes in it.

Regarding noise transmission, the solution is insulating material. Installing joists on a concrete base involves the formation of voids between the beams. They can be filled with a heat insulator or an acoustic analogue, which will dampen sound waves.

Laying insulation between joists on a concrete floor Source nikastroy.ru

To prevent squeaking, it is enough to assemble the most rigid structure possible. The main thing is to correctly determine the loads in advance and select resources in accordance with the calculations. Use only dry timber to avoid future deformation.

Recommendations for choosing lumber

Experts advise giving preference to blanks made from coniferous trees. They contain natural wax throughout, which makes the fibers resistant to moisture and rot. There are also antiseptic components that resist the formation of fungus and mold. Also, such rocks have quite high strength.

Regarding humidity, the recommended limit is 18%. Before laying the logs on the concrete floor, the workpieces are kept inside the workroom for several days. This way, the lumber will undergo an acclimatization procedure, which will further simplify the process of rejecting workpieces. If the timber is not dry enough it will begin to warp. Its craftsmen recommend immediately replacing it with suitable material. Next, the selected timber is treated with antifungal agents and compositions containing fire retardants.

Example of pine timber Source twimg.com

Another selection criterion is the variety. This is a classifier of lumber according to a number of characteristics, which means the permissible number of various types of defects. Thus, timber is characterized by 5 quality categories. But for lags, as a rule, options of 2 or 3 varieties are used. It is possible to be present here:

• a small number of knots and end cracks;
• resin pockets in the amount of up to 4 pieces per linear meter;
• double core;
• sound spots (up to 20%);
• blunt wane along the entire length of the workpiece.

Of course, you can choose selected timber or class Extra, Prima or A. Here, all defects, knots, insect marks and dull wane are either absent or their number is reduced to a minimum. However, the requirements for floor joists are not so high and low grades (except for the last one) are cheaper.

Signs for sorting wood blanks Source potolok-exp.ru

See also: Catalog of companies that specialize in the reconstruction and rebuilding of houses

The cross-section of the timber for mounting the logs on a concrete base is determined by the degree of load on the logs from further finishing, furniture, equipment and people. As a rule, blanks with a thickness of 50-60 mm are used. But there are some recommendations from the masters:

• 40 mm – the side of the beam that is in direct contact with the base;
• 50 mm is the minimum thickness provided that the logs are laid on point supports;
• 75-100 and 100-120 mm – the width of the bars for the first and second options, respectively.

If possible, the length is chosen so as to exclude connecting nodes in the segment between the walls. The direction is most often observed along the short side. But it is worth paying attention to human movement in high-traffic areas. Here the installation is carried out in a transverse position.

An example of the location of the logs across the movement Source superpol-spb.ru

Step width between joists

The pitch between the joists is selected taking into account the thickness of the floorboard. The thicker it is, the larger the step between the bars is allowed. In addition, a thick board sag less under loads.

The table below allows you to quickly select the distances between the bars.

You can also resort to the following rule: when the width of the logs increases by 5 mm, their pitch increases by 10 cm.

When installing plywood, the cross-section of the joist is calculated differently. This is due to the fact that it has great bending strength. With a thickness of sheet material of 1.5-1.8 cm, it is fashionable to place logs against each other at a distance of up to 40 cm. It is necessary to install the beams so that the sheets are fixed at the edges and in the middle. Moreover, the edges of the sheets should fit half the width of the beam.

Carrying out installation work

In the case of wooden products, choosing fasteners is not difficult. Nails and screws are suitable here. When working with concrete, different solutions are required. Let's consider the criteria for choosing fastenings for joists to a concrete floor:

1. Level . The evenness of the rough base determines whether it is necessary to compensate for one or another height. That is, the logs will be laid directly on the floor, attached to the walls or using adjustable devices.
2. Humidity . This criterion applies to the work space. For example, for flooring over a monolith in a bathhouse, it is important to consider samples that will cope with changes in humidity, temperature, and chemical reagents for a long time.
3. Load . The use of floors can vary in intensity and pressure from certain factors.

Another point concerns the floors on the ground floor, which are located above the basement. Condensation often forms under wooden flooring, causing the material to rot. To avoid this, the logs are fixed to supports.

Self-tapping screws

Such fasteners are considered the simplest and most accessible, but their use is not always acceptable.

Example of dowel-nails with nickel plated Source stroikrep.ru

For example, in the case of a support system without direct contact of the timber with the base. The installation process includes the following steps:

• holes of the required diameter are drilled at the location of the hardware (both in the concrete screed and in the wooden blank to prevent the appearance of cracks);
• a plastic dowel is driven into the hole formed in the subfloor;
• the self-tapping screw is screwed through the beam and plunged into the dowel, the head is recessed into the wood a few mm.

The optimal distance between fasteners when using self-tapping screws is 400-600 mm. It is recommended to choose fasteners with a nickel plated diameter of 3.5 mm. The drill bit for the timber is selected with a size of 4-5 mm. The depth of immersion of the dowel into concrete must exceed 50 mm.

Step-by-step instructions for attaching joists to a concrete base with your own hands

The simplest solution for installing a wooden covering over joists is to fasten the profile using dowels.

To carry out the work you will need the following materials:

1. Beam 50 x 70 mm.
2. Dowel-nail 8 x 120 mm.
3. Fiberboard sheet.
4. Polyethylene film.
5. Insulation mats.

Installation work:

1. We clear the room of unnecessary objects and debris.
2. We cut out spacers 100 x 100 mm from fiberboard.
3. Using a water level, we level the floor and mark the locations of the joists on the walls (it is better to mark a solid line along the contour).
4. We prime the surface.
5. We lay plastic film on the base. Each subsequent layer of material should overlap the previous one by 3-5 cm. We seal the joints with tape.
6. We lay out the timber according to the marks on the wall parallel to the window opening. We splice the logs using angles or perforated plates.
7. We begin installation of the structure. To do this, we make through holes in the log furthest from the window, the diameter of which should be equal to the size of the plastic plug of the dowel. The drill must pass right through the body of the wooden profile and also capture 50-70 mm of the concrete base.
8. We press the part tightly to the floor. We check the coincidence of the holes and install the dowel-nail.
9. Use spacers to level the horizontal level according to the marks on the wall and secure the profile with a hammer on the nail head. Using the same scheme, we install the next lag at the doorway. We stretch the cord between them on both sides and continue installation.
10. When all the profiles are laid in place, the gap formed as a result of level adjustment between the base and the joists is sealed with polyurethane foam.
11. We lay insulation mats in the gap between the beams and pre-fix the structure with transverse slats.

Briefly about the main thing

The joists on the concrete floor are fixed directly or at one or another height.

The choice of fasteners is determined by the degree of evenness of the rough base, load and aggressiveness of operating conditions.

If the base is level, then you can use nickel-plated screws and plastic dowels with a length of 50 mm or more or anchor bolts to strengthen the structure.

An alternative to self-tapping screws are mounting angles, with which you can additionally adjust the verticality of the beam and the rise in case of slight deviations of the base in level.

If you need to raise the logs, you can fix them using brackets to the walls or using adjustable fastenings to the floor.

The height of the logs above the floor can be adjusted using plastic stands or studs with counter nuts.

The essence of the operation of adjustable fasteners is the presence of threaded elements and support elements for the beam.

Ratings 0

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What should the cross section of the log be?

The strength of this part of the floor depends on the material of manufacture and the accuracy of load calculations. When choosing the size of the timber, the maximum permissible load on the floor is taken as a basis. For living rooms, this figure is 300 kg per 1 m2. For non-residential premises it is individual in each specific case, so before purchasing the material you need to calculate this indicator.

Basically, timber with a profile aspect ratio of 1.5 x 2 is laid under the floorboard.

The height of the beams must also be selected taking into account the thickness of the insulation. If iron and concrete elements are installed, their cross-section may be smaller. This is due to the fact that these materials are able to withstand high loads for a long time.

Connection fastener

With the advent of modern fasteners made of durable alloy and galvanized steel, many construction processes have been simplified, including the installation of reliable connecting units in timber structures. Some of them have been used for a long time and are traditionally popular. Others appeared relatively recently, so they may be unknown to people whose profession and interests are not related to construction.

Traditional fasteners

The simplest and most reliable of them are dowels or dowels made of hard wood. They blend perfectly with the base material without causing it to deform, crack or rot. In combination with adhesives, they allow for durable fastening.

Assembling a log house on steel dowelsSource remontik.org

Pins are also metal. Their main advantage is their high strength and durability, which is why they are often used to fasten timber crowns vertically.

Nails and staples, which used to be almost the only types of fasteners for wood, are now trying not to be used in the construction of permanent buildings, since the ferrous metal from which they are made is incompatible with wood. It corrodes easily, damaging the wood and gradually deteriorating. For the same reason, it is not recommended to use homemade dowels cut from reinforcing bars.

Modern fasteners

A wide variety of fasteners are made from perforated rolled steel with a thickness of at least 2 mm with an anti-corrosion coating. It is made from:

plates of different lengths and widths with holes for screws and anchors. A large assortment of standard sizes allows you to solve problems such as connecting beams together along a length of 150 by 150, fastening rafters at the ridge part, or strengthening a sagging joint without lower support;

Galvanized connecting plateSource www.sibwindows.ru

• connecting corners from the same source material can be simple or reinforced, with an additional stiffening rib. The range of these products includes both equal-shelf corners and those with different shelf lengths. They are used to strengthen the corner connections of a log house, fasten rafters, floor beams, create a frame for internal partitions, etc.;
• supports are fasteners of complex shapes that allow you to create reliable corner T-shaped joints without making locks. For example, attach floor beams to the walls. Their standard sizes correspond to all standard dimensions of timber sections.

An improved analogue of a perforated plate is a nail or serrated plate. With its help, structural elements located in the same plane are reliably fastened.

Using nail plates, you can assemble trusses and splice timber along the lengthSource cdn.mitekea.com

Threaded rods are also very popular in wooden construction. They tighten the joint by tightening the nuts on both sides of it.

And the most modern fastener, which allows not only to connect the crowns with each other, but also to compensate for the shrinkage of the house and the appearance of cracks between the beams, is the “Strength” spring unit.

Insulation and sound insulation

Soundproofing and insulating floors on beams is quite simple. For example, you can cut TECHNONICOL into strips and lay it between the beams. In this case, the self-adhesive side section that overlaps the beam must be rolled with a roller. For additional insulation of the floor, you can place mineral wool on top of the TECHNONICOL. This sound insulation allows you to protect your living space from noisy neighbors downstairs.

The height should not exceed the bars. In those places where it is higher than the log, its thickness must be reduced. To do this, the cotton wool needs to be cut lengthwise with a knife. If the result is rags, this will not affect the properties of the material.

Atypical situations

Sometimes in old houses, when trying to replace a wooden floor with a new modern design, you have to deal with atypical floor slabs. In these cases, you have to come up with non-standard ways of laying and fastening the lags. One such situation is described in detail in the following video. As you can see, in addition to standard methods of fixing load-bearing beams, you can come up with many more methods. In fact, it doesn’t matter how the logs are attached, the main thing is that they are correctly located in the horizontal plane and can withstand the vertical load.

Base made of concrete and reinforced concrete (laying on an uneven base)

Before installing the logs, the uneven concrete floor is leveled with a cement screed. This technology allows you to make a smooth and reliable base for parquet, laminate or floor tiles, as well as well insulate the floor and protect the room from external noise.

For most floor coverings, a spacing between joists of 60 cm is suitable, but floor tiles require cells measuring 30x30 cm because they are very fragile.

Reinforcing mesh in the screed and spacers between the beams increase the rigidity of the floor. Thermal insulation material can be placed in the resulting cells.

Rules for creating timber strapping

This frame element is made from the following lumber:

• logs;
• timber;
• solid board (double or triple).

The last option is the most durable.
Unlike the other two, it is not susceptible to cracking or warping. The framing of a frame house with a pile or columnar foundation experiences heavy loads, so it is made of high quality wood.

Follow the rules:

1. The width of the element corresponds to the thickness of the wall.
2. Before installation, the timber is treated with an antiseptic and fire retardant impregnation.
3. The foundation is covered with waterproofing.
4. The element is positioned strictly horizontally to achieve uniform load distribution.
5. For fastening to the frame posts, anchors, clamps, U-shaped galvanized profiles and brackets are used.

The frame element is most often made of timber.

Tools

To install the beams, the following tools are required:

• electric drill or hammer drill;
• screwdrivers or screwdriver;
• electric circular saw or simple hacksaw for wood;
• plane;
• hammer;
• tape measure and level;
• fasteners.

Other tools may be required.

Floor subfloor options

These types of floors can be installed on a wooden or concrete base or on the ground. Each option has its own technological features, which must be kept in mind during work. As for the specific purpose of the premises, taking this parameter into account, the base of the floor and its operational characteristics are selected. The technology of the device itself remains almost unchanged. There are, of course, options for warm and cold floors, but these features also have a common construction algorithm.

Video description

What it is and how this spring unit works is described in the video:

When building a wooden house, the question always arises of how to connect two beams lengthwise or fasten a corner. Each master has his own preferences in this matter: one adheres to methods that have been proven over centuries, the other trusts more modern methods using special fasteners. And this issue needs to be discussed in advance, after independently studying all the possible options and deciding what is your priority: speed and reasonable cost of installation or quality and reliability.