How to block a 6 meter span. Overlapping large spans with wooden beams: glued beams, wooden trusses. What are wooden floors

Floor Span Table

The table of spans of floors of a frame house helps to choose the correct cross-section of the floor log, which means avoiding problems with floor sagging, creaking and vibration when walking. Our home-grown approach - to take larger beams - is not economically justified. A board is cheaper than a bar, especially a large section. Most often, the length of the floor spans is within 3.5-4.5 meters and, observing the correct section and pitch, you can install a reliable overlap.

Let me remind you that floor logs are placed with a certain step, which is a multiple of the long side of the rough sheathing slab, namely 305 mm, 407 mm, 488 mm and 610 mm for osb / plywood slabs of 2240 x 1220 mm.

For 305mm pitch (12 "OC)

For pitch 407mm (16 "OC)

For 488mm pitch (19.2 "OC)

For 610mm pitch (24 "OC)

Where did the data in these tables come from?

How to work with tables correctly and what is residential and non-residential load?

Living room is everything that is located and moves through the overlapping space: people, objects. Non-residential load is the weight of the building elements. For example, the weight of the log floor and subfloor slabs.

Depends on what will be located on top: a double bed or a regular chair. The floor finish can be a light laminate, or there can be a heated floor screed with tiles.

Typically, for residential premises, the total load is in the range of 200-250 kg per sq.m. If you plan to install a cast-iron bathtub, then look at its weight and add a lot of water and yourself in it.

For which wood species are these values taken?

Since our markets do not have a quality system and an accurate determination of the grade of sawn timber, the tables show the values for ordinary spruce and pine of the II grade according to the North American classification.

The actual dimensions of the section of the boards in the American tables are smaller than the European ones, what should I do?

This is true. If Americans say a 2 "x 6" board is not 50.8mm x 152.4mm. In fact, it is 38.1 mm x 139.7 mm. Reducing the section of the board occurs as a result of drying and planing. At our sawmills, timber yards and markets, there is also no furniture store. Sellers say that the board is 50 mm x 150 mm, but in fact it can be 40-50 mm x 135-150 mm.

Among the many structural elements of a private house, the overlap is one of the most critical and difficult for design and installation of units. It is here that inexperienced builders make, perhaps, the most dangerous mistakes, it is precisely on the arrangement of this system that the most questions are asked.

1. Why choose a tree

In any building, the floor is a horizontal structure, which acts as the basis for the creation of the floor. In addition, being tied to the load-bearing walls of the house, it provides the structure with lateral stability, evenly distributing possible loads. Therefore, the highest requirements are imposed on the reliability of this design.

Regardless of what material is used in the construction of a house, in the private sector, the most widespread are just wooden floors. They can often be seen in various stone cottages, and it is quite obvious that in wooden construction (log, timber, frame and frame-panel technology) there is no alternative to such a solution. There are many objective reasons for this. Consider the advantages and disadvantages of wood floors.

In private low-rise construction, floors are mounted in several versions:

Finished reinforced concrete slab,
Monolithic reinforced concrete slab,
Prefabricated reinforced concrete beams,
Rolled metal beams and trusses,
Overlapping from sawn timber.

pros

Or why hardwood floors are so popular.

Light weight. Using a board or timber, we do not overload the load-bearing walls and foundation. The weight of the floor is several times less than that of concrete or metal structures. Usually, the involvement of technology is not required.
Minimum terms of work execution. The minimum labor intensity among all options.
Versatility. Suitable for any building, in any environment.
Possibility of installation at subzero and very high temperatures.
Lack of "wet" and dirty processes.
Possibility of obtaining any level of heat-insulating and sound-insulating characteristics.
Possibility of using cavities for laying engineering communications (power grid, heating, water supply, sewerage, low current ...).
Relatively low price of prefabricated timber frame slabs, both in terms of the cost of parts / components, and in terms of remuneration of the contractor.

Minuses

The disadvantages of a wooden overlapping system made of wood are rather arbitrary.

The complexity of the choice of the cross-section of materials and design solutions to ensure the design bearing capacity.
The need to carry out additional fire-fighting measures, as well as to ensure protection from moisture and pests (antiseptic).
The need to purchase soundproofing materials.
Strict adherence to technology to avoid construction mistakes.

2. What material to use for assembly

Wooden floor - always consists of beams. But they can be made from a wide variety of lumber:

Round logs up to 30 cm in diameter.
The bar is four-edged.
Large section board (from 50 mm thick, up to 300 mm wide).
Several boards of relatively small thickness, twisted in layers to each other.
I-beams, the upper and lower chords of which are made of edged planed board / bar, and the vertical wall is made of OSB-3, plywood or profiled metal (wood-metal product).
Closed boxes made of sheet materials (plywood, OSB).
SIP panel. In fact, these are separate sections in which the beams are already sheathed and have an insulator inside.
Various truss designs to cover large spans.

The easiest for installation, as well as the cheapest and most convenient for performing subsequent operations, are options when the floor beams are made of edged sawn timber.

Due to the very high requirements for bearing capacity, durability and geometric deviations, it is necessary to consider first grade sawn timber as blanks. It is possible to use products belonging to the second grade in accordance with GOST, which do not have critical geometric deviations, defects and processing defects that can reduce the strength characteristics and service life of finished parts (through knots, curl, cross layers, deep extended cracks ...).

In these designs, the use of dead wood (dead wood, dead wood, burnt wood) is excluded due to insufficient strength and multiple lesions by diseases and insects that destroy wood. It will also be a big mistake to buy a timber or board "with air", "with an Armenian size", "TU" - due to the understated sections.

It should be an exceptionally healthy material from green spruce or pine, since the needles, due to their resinous content and the structure of the massif, tolerate bending loads and compression much better than most hardwoods, and having a relatively low specific gravity.

In any case, edged lumber must be freed from the remnants of bark and bast fibers, treated with an antiseptic and fire retardant. Dry planed sawn timber will show itself best here, but the material of natural moisture (up to 20 percent) during normal processing is also actively (and most importantly, efficiently) used, especially since the price of edged timber or boards of this type is noticeably lower.

3. How to choose the size of the beams and with what step to arrange them

The length of the beam is calculated in such a way that it overlaps the existing span and has a "margin" to support the load-bearing walls (see below for specific numbers of permissible spans and entry into the wall).

The section of the board / timber is determined depending on the design loads that will be exerted on the floor during the operation of the building. These loads are divided into:

Permanent.
Temporary.

Temporary loads in a residential building include the weight of people and animals that can move along the ceiling, objects being moved. Permanent loads include the mass of the lumber of the structure (beams, logs), floor filling (insulation / noise protection, insulating sheets), hemming (roll-up), rough and final flooring, finishing flooring, partitions, as well as built-in communications, furniture, equipment and household items ...

Also, do not lose sight of the possibility of storing objects and materials, for example, when determining the bearing capacity of the floors of a non-residential cold attic, where unnecessary, rarely used things can be stored.

The sum of permanent and temporary loads is taken as a starting point, and a safety factor of 1.3 is usually applied to this. The exact figures (including the section of lumber) should be determined by specialists in accordance with the provisions of SNiP 2.01.07-85 "Loads and Impacts", but practice shows that the values of loads in private houses with wooden beams are approximately identical:

For interfloor (including under a residential attic) and basement ceilings, the total load is about 350 - 400 kg / m2, where the share of the structure's own weight is about 100 kg.
To cover an unloaded attic - about 130 - 150 kg / m2.
For overlapping a loaded non-residential attic up to 250 kg / m2.

Obviously, unconditional security is paramount. Here a good margin is taken into account and the option is considered not so much distributed loads on the entire floor (in such quantities they are practically unrealistic), but the possibility of a local load that can lead to deflections, which in turn caused:

physiological discomfort of residents,
destruction of units and materials,
loss of aesthetic properties by the design.

By the way, certain deflection values are allowed by regulatory documents. For residential premises, they can be no more than 1/350 of the span length (that is, 10 mm at 3 meters or 20 mm at six meters), but provided that the above listed limiting requirements are not violated.

When choosing a section of lumber to create a beam, they are usually guided by the ratio of the width and thickness of a bar or board in the range of 1 / 1.5 - 1/4. Specific figures will depend, first of all, on: loads and span lengths. When designing yourself, you can use the data obtained on the basis of calculations using online calculators or publicly available tables.

Optimal average cross-section of timber floor beams, mm

Span 3 mSpan 3.5 mSpan 4 mSpan 4.5 mSpan 5 mSpan 5.5 mSpan 6 m

As you can see, in order to increase the bearing capacity of the floor, it is enough to choose lumber with a greater width or greater thickness. Including, you can assemble a beam from two boards, but so that the resulting product has a cross section not less than the calculated one. It should also be noted that the load-bearing properties and stability of a wooden floor is increased if logs or various types of subfloors are used over the beams (plywood / OSB or edged boards).

Another way to improve the strength properties of a wooden floor is to reduce the spacing of the beams. Engineers in their projects of private houses determine in different conditions the distance between the beams from 300 mm to one and a half meters. In frame construction, the spacing of the beams is made dependent on the spacing of the racks so that there is a rack under the beam, and not just a horizontal strapping run. Practice shows that the most expedient from the point of view of practicality and cost of the structure is a step of 600 or 1000 mm, since it is best suited for the subsequent installation of heaters and soundproofing of spores (insulating materials have just such a form factor of plates and rolls). This distance also creates the optimal distance between the support points for installing floor logs installed perpendicular to the beams. The dependence of the section on the step is clearly visible from the figures in the table.

Possible cross-section of floor beams when changing the pitch (total load per square meter is about 400 kg)

4. How to install and fix the beams correctly

We decided on a step - from 60 centimeters to a meter will be the golden mean. As for the spans, it is best to limit yourself to 6 meters, ideally four to five meters. Therefore, the designer always tries to "lay" the beams along the smaller side of the house / room. If the spans are too large (more than 6 meters), then they resort to installing load-bearing walls or supporting columns with crossbars inside the house. This approach allows you to use lumber of a smaller section and increase the spacing, thereby reducing the weight of the floor and its cost for the customer with the same (or better) bearing characteristics. Alternatively, trusses are created from lighter lumber using metal perforated fasteners, for example, nail plates.

In any case, the beams are exposed strictly horizontally, parallel to each other, with the same step. A wooden beam must be supported by at least 10 centimeters on load-bearing walls and girders. As a rule, 2/3 of the thickness of the outer wall is used from the side of the room (so that the end of the beam does not go out into the street and remains protected from freezing). In wooden walls, a cut is made, in stone walls, openings are left during masonry. In places where the beams of the supporting structures touch, it is necessary to lay insulating materials: damping elastic gaskets made of rubber / felt, several layers of roofing material as waterproofing, etc. Sometimes they use firing of subsequently hidden sections of the beam or their coating with bituminous mastics / primers.

Recently, special perforated brackets "holders / supports of the beam" are used more and more actively to create the floor, which allow you to mount the beam end-to-end with the wall. With the help of this type of brackets, nodes are also assembled with transverse crossbars and beams truncated in length (opening for a flight of stairs, chimney passage, etc.). The advantages of this solution are obvious:

The resulting T-joint is very reliable.
The work is done quickly (cuttings do not have to be done, it is much easier to set a single plane).
Cold bridges are not formed along the body of the beams, because the end face moves away from the street.
There is an opportunity to buy lumber of a shorter length, since there is no need to start the timber / board inside the wall.

In any case, it is very important to thoroughly antisept the end of the beam after adjusting the lumber to size.

5. What kind of insulating layers should be used inside wooden floors

To answer this question, first of all, the overlapping structures (in a year-round inhabited house) should be divided into three separate types:

Basement overlap,
Interfloor,
Attic.

In each case, the set of the cake will be different.

Interfloor floors in the overwhelming majority of cases separate rooms in which the temperature regime is similar or close in value (if there is room / floor / zone control of the heating system). These also include the attic floor, which separates the residential attic, since this room is heated, and the insulation is located inside the roofing pie. For these reasons, thermal insulation is not needed here, but the issue of combating noise, air (voices, music ...) and percussion (steps, rearrangement of furniture ...) becomes very relevant. As sound insulation, acoustic fibrous materials based on mineral wool are placed in the ceiling cavity, and sheets of soundproof membranes are also covered under the cladding.

The basement structure assumes that under the overlap there is a soil or basement, cellar, basement floor. Even if an exploited room is equipped below, this type of overlap needs full-fledged insulation, inherent in the enclosing structures of a specific climatic zone and a specific building with its unique thermal balance. According to the norms, on average for the Moscow region, the thickness of a modern insulation with good thermal conductivity will be about 150-200 mm.

Similar requirements for thermal insulation are imposed on the attic floor, above which there is no heated attic, because it is he who will be the main barrier on the way of heat losses through the roof of the building. By the way, due to the greater flow of heat through the upper part of the house, the thickness of the insulation here may be required more than in other places, for example, 200 mm instead of 150 or 250 mm instead of 200.

They use polystyrene, EPS, mineral wool with a density of 35 kg / m3 in slabs or cut with mats from a roll (the one that is allowed for use in unloaded horizontal structures is suitable). Thermal insulation is laid between the beams, as a rule, in several layers, with the bandaging of the joints. The load from the insulation is transferred to the beam through a rough hem (often it is attached to the beams by means of cranial bars).

Where a watt-type insulation / sound insulator works in structures, it should be protected from moisture. In the basement floor, moisture can rise in the form of vapors from the ground or from the basement / cellar. Water vapor can enter the interfloor floors and attic, which always saturates the air of living quarters in the process of human everyday life. In both cases, a construction vapor barrier film must be laid underneath the insulation, which can be ordinary or reinforced polyethylene. But, if thermal insulation is performed using extruded polystyrene foam, which does not have any significant level of water absorption, then vapor barrier is not needed.

From above, insulation and fibrous sound-insulating materials are protected with waterproof sheets, which can be membranes or non-perforated waterproofing.

A reliable hydro-barrier is especially relevant in rooms with high humidity: kitchen, laundry, bathroom ... In such places it is spread over the beams, always with 100-150 mm overlap of strips and gluing the seam. The canvases around the entire perimeter of the premises must be installed on the wall - at a height of at least 50 mm above the finishing coating.

The overlap, which will later be tiled with tiles, it makes sense to supplement with a rough flooring made of waterproof sheet materials - various types of cement-containing slabs, preferably grooved. On such a continuous flooring, you can carry out additional coating waterproofing, perform a thin-layer leveling of the plane with a leveling compound or immediately lay tiles.

You can choose another option - to assemble a continuous flooring from an edged board, lay a hydro-barrier, fill in a thin-layer screed (up to 30 mm), and mount a lath.

There are also modern adhesives (and elastic grouting) that allow tiling wooden substrates, including movable and heated ones. Therefore, tile floors are often implemented here on moisture-resistant plywood or OSB.

Important! Taking into account the increasing loads (general or local - a large bath, a jacuzzi bowl, a floor-standing boiler ...), the calculation of the cross-section and spacing of the beams under such rooms must be performed individually.

If desired, the floors in the bathroom or in the kitchen of a wooden house can be equipped with a heating cable or pipes for the water circuit of the heating system. They are mounted both in screeds and a layer of tile glue, and between the lags in a deliberately created air gap. With any option chosen, the ceiling should be well insulated so as not to heat the ceiling of the room from below, preferably equipped with waterproofing with a reflective foil layer.