Floor insulation in a wooden house: technology and pie

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Today we will consider one of the most popular schemes for installing an insulated floor in a wooden house. The review will raise key questions about the preparation and arrangement of the substructure of the floor, the insulation cake and its protection, as well as the correct flooring of the natural board cover.

Thermal insulation of the floor in a wooden house with mineral wool

Requirements for the supporting floor system

High-quality insulation of a wooden floor requires that the configuration of its subsystem (lag, supports, jumpers) match the available dimensions and form factor of the insulation. Expanded polystyrene and mineral wool are considered the most suitable for insulating a wooden floor, less often bulk granular fillers such as ecowool or perlite chips are used. The design of the floor supporting system must allow the insulation to be securely fixed, ensure its immobility and at the same time maintain its strength and functional purpose.

Floor insulation in a wooden house: technology and pie

The key to creating a reliable and durable insulated floor is good fixing of the logs and providing solid support for them. If the floor is arranged on the ground, it is necessary to place a series of support pedestals, made of bricks or cast in reinforced concrete. To simplify installation, the edges of the lag are supported on the projections in the strip foundation. They can be made with a perforator and angle grinder, and then sealed with cement mortar, or provided at the stage of formwork assembly. An expansion gap of about 1/4% of the length of the log should remain between the end of the beam and the entire foundation..

Laying logs of a wooden floor 1 – strip foundation; 2 – support posts; 3 – waterproofing; 4 – floor logs; 5 – waterproofing lag

It is also necessary to make sure that the moisture contained in the stone elements of the structure – the foundation and the supporting pedestals – will not migrate into the wood. To do this, use lining of 2-3 layers of roll waterproofing. You should focus on wood processing before starting installation work. All lumber must be thoroughly impregnated with antiseptics and, if necessary, fire retardants, and then dried in a stack.

Lags and counter grill

When installing the lag, they are placed with a step corresponding to the format of the insulation used. To avoid the frequent installation of support pillars, you can use a cross lag system. In this case, the lower beams have a cross-section with equal sides and perform the main load-bearing function. The upper row has a frame device: the boards, placed on the edge, form longitudinal cells, convenient for laying insulation of a certain width and fastening the floorboards.

Frame house floor

If the house is located on a slab foundation, then the supporting floor system has the simplest device. Lags are formed by one frame row, which is anchored to the concrete base. The plane of the monolithic base forms the bottom for the cells for the insulation, ensuring its reliable fixation.

Concrete floor insulation

When constructing a floor on the ground, there is no such reference plane. One of the options to arrange it is to fill with a light porous material, such as expanded perlite or expanded clay, to the lower level of the lags.

Floor insulation on the ground

Otherwise, the logs that form the cells for the insulation are equipped with longitudinal stops. A bar of about 25×25 mm is screwed with self-tapping screws at the bottom of each log, forming parallel ledges. A shingle mesh or a thin edged board is laid on them, due to which the support of the insulation is provided.

Floor insulation in a wooden house 1 – cranial bar; 2 – floor lag; 3 – mesh; 4 – vapor barrier; 5 – insulation; 6 – floor board

Floor insulation in a wooden house

It is important to know that since the stuffed bars “eat up” the space of the floor cells a little, the remaining height may not be enough to accommodate the insulation of such a thickness, which is provided by the heat engineering calculation. In this case, bars of the same size are stuffed over the edges of the frame system. They can be located parallel or across the top row of the logs, in the latter case, an additional gap is provided for ventilation of the insulation.

Insulation bookmark

The width of the cells for laying mineral wool mats should be 1–2% less than the dimensions of the insulation. Due to the tight fit, excessive floor ventilation is eliminated and the possible shrinkage of the cotton wool over time is compensated. When laying the mats, they must be carefully and evenly squeezed across the plane, put into the cavity and then straightened inside. It is desirable that after laying the cotton wool forms a small hump, protruding upwards, which will be pressed by the boards. If foil wool is used, it is placed with the reflective surface up.

Thermal insulation of a wooden floor with mineral wool

In the case of expanded polystyrene, which is practically not compressible, slight gaps may form. They are eliminated by blowing in summer foam at the end of filling all the cells. Too thick gaps in order to reduce foam consumption can be eliminated with thin cut-out inserts made of EPS.

Floor insulation with expanded polystyrene

To backfill the insulation in the space between the lags, it is necessary to localize the cells by covering the bottom with a vapor-permeable membrane with a turn on wooden beams. In its simplest form, a geotextile or vapor barrier can be used to protect roofs. To prevent the membrane from shifting when filling the insulation, it is recommended to shoot it with staples to the wooden elements of the floor system.

Thermal insulation of a wooden floor with ecowool

How is heat insulator protection performed?

Various insulation and ventilation schemes may require limited air circulation in the space under the floor. This is especially true for houses on a pile-grillage foundation, where the insulation is in contact with the outside air and must be protected from getting wet..

So that mineral wool does not lose its heat-saving properties when saturated with moisture, it is covered with a vapor barrier on top. The protective membrane is spread over the log and insulation, then fixed to the wooden blocks with small nails or staples. The joints must be carefully glued on both sides, it is better if they are located exactly on the edges of the floor supporting system.

Insulation vapor protection

In those rare cases when the dew point can move above the insulation with the formation of condensation on the vapor barrier, it is necessary to provide airflow under the flooring from the boards. It is necessary to fill over the frame logs covered with a vapor barrier, a counter-lattice made of boards of the same width as the logs themselves. The thickness of the air vent usually does not exceed 20-25 mm, the counter-lattice itself does not in any way affect the quality of fixing the flooring from the boards.

We lay the grooved board

The insulated frame floor system has solid wood elements that serve as excellent cold bridges. To prevent heat outflow, you can cover the frame system of the floor with a heat-insulating and moisture-resistant material, such as GVLV or MGL, and then lay the boards, having previously outlined the position of the lag.

Grooved board

For an insulated floor, it is recommended to use a grooved board with expansion grooves on the seamy side. Such a flooring will not creak when walking, it is less susceptible to uneven shrinkage and warping. Due to the tight joining of the boards, any kind of blowing between them is excluded. If limited air circulation is planned under the floor, then the holes for its inflow will be 10-15 mm distance gaps near the walls, which also serve to compensate for the linear expansion of the wood.

Laying grooved boards

When decking, a ridge is cut from the end of the first board, the groove is oriented towards itself. Fastening is carried out in each lag, one or two points. The boards are fixed with ragged nails, which are hammered obliquely into the groove and finished off, guiding a steel bar. For high-quality rallying of boards of 20-30 cm in front of them, a timber is temporarily attached to the logs and loose floorboards are squeezed from it with a lever or a car jack.

Floor board screed

The last plank of the set is cut to fit the remaining gap, taking into account the curvature of the walls. It is squeezed from the wall by mounting through a lining of a wooden bar, and then attached to the logs right through from the surface. Traces from fastening with nails are subsequently covered with a plinth.

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