How to properly insulate the floor in a wooden house

Recommendation points

• Classic floor arrangement
• Floor with subfloor on piles
• Floor frame system
• Floor in bathrooms
• The difference in the use of insulation

There are several floor systems for a wooden house, both typical and quite specific. Today we will analyze the most popular of them in terms of the most profitable method of insulation. Let’s talk about materials, cake and carrier system.

Classic floor arrangement

Initially, the floors in wooden houses were bulk, which did not have a very good effect on the life of the residents and the efficiency of cleaning. Therefore, they began to deepen the floor inside the house and prepare a dense incompressible bedding. Logs or sleepers were laid on top of it, with a half-wood cut and a checkerboard ligation pattern, and already on top of it, a plank board of the main covering was laid, which was then leveled, simultaneously filling up the cracks.

Such a floor, for all the simplicity of its construction, has one drawback: it is cold and in terms of heat saving it is not much better than open ground. Therefore, more and more often, a system of transverse lathing or digging under the beams began to be arranged for free air circulation. The floor did not adjoin the walls and the stove, due to which the room air circulated under it, equalizing the temperature difference between the wood and the ground to an average value of 15–20? С.

Unfortunately, this approach only works with the abundance and availability of fuel. Modern fireplace and radiator heating systems designed to save energy resources do not provide adequate heating. In addition, the floor level in the house was below ground level, which caused trouble during floods, and the need for free circulation near the walls did not allow closing the junction with a plinth.

Yet such primitive systems formed the basis for two typical wood flooring techniques that are used in most construction projects. Their main difference is the use of highly effective insulation techniques, which would have been impossible without a well-thought-out supporting system that allows you to correctly place and fix the heat-insulating material without losing the height of the premises.

Floor with subfloor on piles

It is possible to slow down the transfer of heat from the plank flooring to the ground by increasing the air gap and covering the ground with even a small layer of material that does not transfer heat well.

In this case, the floor is arranged in the same way as floating on a continuous bedding, but at the same time a rigid support is installed under each intersection of the lag. In modern construction, the implementation of such a system is undertaken by piles: screw or manufactured using TISE technology..

At the same time, the soil in the building is significantly underestimated, which is quite normal for an old well-established log house without a foundation with girth logs. In the more modern MZLF, exposing one face of the foundation is unacceptable – torsional and lateral loads appear, for which working reinforcement is almost never provided. Therefore, the floor log system is installed in two levels: the first with beams in the spacer inside the tape, and the second with boards on the edge, over the tape and the log.

If heating the subfloor by circulating room air is not planned, the upper row of the lag is covered with synthetic burlap, supported by strips stuffed on the lower row. Insulation, including bulk insulation, can be laid in the cells of the floor lag. If it is necessary to increase its thickness, a counter-lattice is packed.

To reduce the volume of soil removed and support the foundation, a dump is left under it a meter wide and 40-50 cm high, but no closer than 20 cm to the rear surface of the boards. Expanded clay or perlite mixed with lime, as well as more natural materials, can be used as heat-cutting off fillings. For example, reeds, straw or moss, dried and sprinkled with dry sand, then laid on a layer of waterproofing.

Floor frame system

When constructing a wooden house on a pile-grillage foundation, the option with an underground floor disappears by itself. This requires a system that is able to reliably lock the heat inside and allow the use of floor heating, at least under the influence of natural convection..

The problem is solved by installing a crown made of logs on the foundation, knocked down like a frame for a floating floor: with undercut and run-off. These logs play the role of a second grillage, but their cell is smaller – about 100–120 cm versus 4–5 meters for concrete beams under load-bearing walls. When laying logs on top of the grillage, they are separated by several layers of waterproofing and a windproof membrane with good vapor permeability is pulled.

The next task is to knock the windshield with slats to the lower surface of the log. Although you can get to the logs through the ventilation gap under the grillage, working in cramped conditions and in poor lighting is still a challenge. Do not fasten the strips with self-tapping screws, they will wind the windscreen around themselves. Use 10mm shingles and small ragged nails instead..

The insulation of the floor has the same thickness as the logs of a wooden grillage. A mineral filler with a low density is usually used here, in the classic version it is several layers of rolled cotton wool. To support heavier materials, the cell can be upholstered from the inside with a polymer mesh or a wire screwed onto press washers.

1 – straps for filing wind protection; 2 – lags; 3 – wind protection; 4 – mineral insulation; 5 – vapor barrier; 6 – sandwich panel

When the thickness of the beams is from 120 mm, after laying the insulation, they can be covered with a vapor barrier, and then the floor can be laid with sandwich panels with a mineral or polymer core. In the floor system, logs from boards to the edge can also be provided if the thickness of the insulation is not enough based on the results of the heat calculation.

Floor in bathrooms

The biggest problem in a wooden house is the need to cast a preparatory screed. And if, for floor heating, the accumulating screed is cast after the device of a compensation layer over the subfloor with total waterproofing, then how to lower the floor in the bathroom by the required 50 mm?

Intervention in the floor system is indispensable here. In frame houses, the bathroom is arranged in a separate cell of the grillage, but it is cast deaf, possibly with transverse ribs. The depth of the cell should be sufficient for laying the required amount of synthetic insulation, routing the drainage system and, at least partially, for rough plumbing.

Further, the classic scheme of a frame floor with a screed operates: logs and flooring or self-supporting insulated wire, waterproofing, pouring a cement-sand mixture or expanded clay concrete with lightweight reinforcement. A separate plus of such a system is the ability to easily arrange a common floor drain.

1 – cranial bar; 2 – boardwalk; 3 – lag; 4 – vapor barrier; 5 – insulation; 6 – OSB flooring; 7 – waterproofing; 8 – reinforced screed

In houses with strip foundations, the same principle. If the walls of the bathroom are solid, at least a tape is poured under them, separating the insulated screed in the bathroom from the main floor system. If we are talking about prefabricated partitions, they are built along the subfloor flooring, the butt end is closed with a board and again an insulated screed is poured over the ground.

The difference in the use of insulation

Since mineral and polymeric foam insulation is now being promoted by manufacturers equally diligently, the specifics of working with them are modestly silent. The key criteria for choosing a material for insulation are resistance to heat transfer, resistance to wetting, fire hazard and the likelihood of pests settling under the floor.

Expanded polystyrene and polyurethane foam provide benefits in durability and insulation efficiency. They can harmlessly take on the condensation point, even when sealed in a cake. The only drawback is the price: insulation will cost about a third more, and the more affordable PSB is toxic when heated and requires protection from rodents.

Mineral insulation is very sensitive to moisture saturation. If they are operated at the border of two temperatures, then from the side of the room they must be insulated with a vapor barrier and the circulation of street air through the cotton wool should be limited.