Thermal insulation of basement walls

With the current practice of using basements – as guest rooms, reception halls, rooms for amateur classes or workshops – a comfortable microclimate is achieved without energy loss only if all elements of the building in contact with the ground are thermally insulated. It is quite legitimate one of the main regulatory documents – SNiP II-3-79 “Construction heat engineering” – requires the use of heaters for rooms adjacent to the ground.

Fig. 1
In a detached cottage, in the absence of thermal insulation around the perimeter of the foundation, up to 20% of all heat losses can occur in the area of ​​the heated basement.

All other things being equal, the most advantageous is the continuous external thermal insulation of the basement (thermal insulation of the perimeter). If the thermal insulation is entirely located outside the waterproofing, then both the waterproofing itself and the elements of the structure receive additional durable protection from mechanical and thermal effects.

If, along with thermal insulation, soil drainage around the building is required, then one of the possible solutions may be the use of non-woven geotextiles of the Typar (r) group manufactured by DuPont (USA) based on endless polypropylene fiber..

Fig. 2
Basement of the building insulated with extruded polystyrene foam

The use of thermal insulation (if necessary, with additional drainage) is necessary not only for the construction of cottages, but also for the construction of apartment buildings, administrative and industrial buildings with heated basements, even if the share of heat loss through the basement in the total balance is relatively small. External thermal insulation of the basement walls is economically feasible even if the operation of the premises is not planned immediately after the end of construction.

Extruded polystyrene foam materials have been used for perimeter insulation for over 20 years. Immediately, we will stipulate that the perimeter of a building means those elements of it (walls and floor) that are in contact with the ground. Long-term research confirms the effectiveness of their use in extreme operating conditions. Currently, more and more architects and builders are attracted by the advantages of the company’s perimeter system, which includes thermal insulation and mechanical protection of the outer walls of basements..

Fig. 3
The embossed surface of the insulation boards promotes better adhesion of the plaster

Extruded polystyrene foam is especially beneficial for the perimeter zone, where the building elements, due to contact with the ground, must meet particularly stringent requirements for moisture resistance, thermal insulation, aging resistance, strength, resistance to freeze-thaw cycles.

Due to the closed cell structure, the extruded polystyrene foam boards have a number of advantages:

• low thermal conductivity;
• high compressive strength, allowing to withstand significant ground pressure and use the material on a large
• depth of laying;
• dimensional stability;
• insensitivity to moisture and almost complete absence of water absorption;
• not susceptible to aging processes;
• ease of processing.

Application experience has shown that products made of extruded polystyrene foam are reliable at depths of more than 7 m (depending on the brand), as well as with prolonged contact with water under pressure..

If the outer walls of the basement only need thermal insulation, and drainage is not required, or is carried out by the usual method (for example, through a filtering layer of gravel), then in this case it is effective to use extruded polystyrene foam plates over the waterproofing, which provides additional mechanical protection.

It is recommended to insulate the basement of the building with extruded polystyrene foam, followed by plastering on a grid. The embossed surface of the boards promotes better adhesion of the plaster (fig. 3).

When installing the thermal insulation of the foundation slab, the extruded polystyrene foam is laid directly on a clean leveling layer and covered with a polyethylene film with an overlap along the edges, and then monolithic. If especially high requirements are imposed on the strength of the insulation during compression, then we recommend choosing the appropriate brands of thermal insulation boards. Using hydro-technical concrete, insulation slabs can be laid directly into the formwork.

Fig. 4
1 – heat-insulating plates with an embossed surface;
2 – heat-insulating plates;
3 – basement wall (porous block masonry);
4 – vertical waterproofing;
5 – plaster of the basement part;
6 – composite heat-insulating plates;
7 – horizontal waterproofing;
8 – clean leveling layer;
9 – filter gravel;
10 – separating layer (polyethylene film, road paper);
11 – base plate;
12 – monolithic concrete layer;
13 – flooring;
14 – plinth;
15 – drainage pipe;
16 – backfilling.

Plates of extruded polystyrene foam are often used in conditions of prolonged contact with water under pressure and under foundation slabs. The accumulated positive experience allows us to consider this decision economically the most justified.

The advantages of a perimeter thermal insulation system using extruded polystyrene foam boards are:

• protection of waterproofing from mechanical damage during the construction phase;
• protection of building elements during its operation, and thereby ensuring its long-term preservation;
• preventing water from entering the outer walls;
• ease of installation; it can be produced regardless of weather conditions;
• insignificant water absorption and high thermal insulation properties;
• resistance to acidic compounds in the soil;
• high compressive strength, including under continuous load;
• unaffected by the aging process.

Technology for working with plates made of extruded polystyrene foam: before backfilling the pit, the thermal insulation boards are attached to the outer surface of the basement walls by point fixing using a solvent-free adhesive. The gluing of the slabs can be considered as a purely assembly auxiliary operation, since in working condition the slabs are tightly pressed against the walls of the basement due to the support of the soil.

Thermal insulation of the foundation is carried out in the same way: plates of extruded polystyrene foam are placed directly on the leveling clean layer (Fig. 4). A plastic wrap is spread over them with an overlap along the edges. Next, concrete is poured, forming a monolith of the foundation slab. This completes the installation.