Insulating the foundation of a house from the outside is the best method of saving the foundation of a building

Insulating the foundation of a house from the outside is the best method of saving the foundation of a building Insulating the basement of the house from the outside is the best method of saving the base of the building

When you decide questions thermal protection of a house in a complex, among the different options, owners and contractors most often prefer the popular method of insulating the foundation of a house outside with expanded polystyrene.

There are other techniques, but unlike wall insulation, not all standard materials for thermal insulation are used here - the features of the conditions of use and a much larger range of tasks impose some restrictions.

Since the foundation has more than just an underground part, sometimes a combination of certain technologies is required. How and what to cover the foundation from the outside in order to reduce heat losses, we will consider in the article.

Why insulate the foundation?

Heat losses through the base are small - about 5-15%.

Its position affects, as well as the physical features of heat transfer. There are only three methods of transferring heat energy - radiation, convection (for liquid and gaseous media) and thermal conduction. Radiation is definitely not about the foundation, but about the installation of the heating system. They have a higher temperature in comparison with air and environmental objects, and they also serve as sources, and not as receivers.

But the walls of a heated room in the winter season are capable of radiating energy into the street.

in the infrared spectrum. To see this background, you just need to look at them with a thermal imager. It is extremely bright in non-insulated areas and cold bridges. Convection of a natural type is characterized by an upward heat flow of air and a downward one - cold air. Naturally, the temperature of the foundation cannot affect such a process.

It is important to insulate the ceiling and roof so that they do not quickly cool the warm air. Of the above methods of transferring heat energy, it is precisely due to the thermal conductivity of construction materials, a cool foundation affects the loss of heat and the cost of heating the house.

And the thermal conductivity of reinforced concrete, from which the foundation is usually made, is quite high, and therefore its low temperature is transmitted to the load-bearing partitions and walls. The air in the room cools down due to the enclosing structures, which will give off heat to the surrounding world. For an underground foundation element, this is soil, for walls and a basement, it is air.

Insulation of the foundation will reduce such losses.

In the video, you will learn more about the heat loss of a building and what are the goals of warming the foundation. But there is another function of thermal insulation of the base of the building - the life of the foundation increases. Building materials have a certain criterion, namely frost resistance. Its numerical expression will indicate how many freezing cycles (assuming saturation with water) must pass before even small signs of destruction appear.

For this reason, for regions with long and cool winters, insulation and waterproofing of the base is a prerequisite in order to ensure the strength and durability of the structure.



Are there two types of foundations that will be subject to insulation - tape and slab. For pile and columnar foundations, we can talk about the thermal insulation of the floor on the first floor and the filling, or rather the basement - to some extent of the screen that will protect the subfloor. But the pillars and piles themselves do not insulate.


The technology for insulating the base of the slab is no different from the thermal insulation of concrete floors on the ground:

  • Solid base made of rammed earth.

  • Geomembrane as protection against capillary rise of water in the ground.
  • A cushion of sand and rubble to improve the bearing capacity of the earth and to distribute the load correctly.
  • Roll type of waterproofing.
  • Sheet-type insulation (EPS, that is, expanded polystyrene).
  • Stove.

The Swedes could slightly improve the technology and at the stage of pouring the foundation they mount a "warm floor" in slabs. We often do it as before - in a concrete screed or under the final floor covering. Scandinavians are boring people and already know in advance where they will have not only partitions, but also pieces of furniture (one of the criteria for the correct functioning of warm floors). Russian people have a different character and mentality - they are not just pieces of furniture, but even the walls inside an apartment / house are often transferred from one place to another.

Strip-type foundation

Do-it-yourself foundation insulation outside has a huge selection of technologies and materials:

  • Insulating the foundation of a house from the outside is the best method of saving the foundation of a building Fixed formwork type.

  • Fastening foam sheets or even extruded polystyrene foam.
  • Spraying with liquid polyurethane foam.
  • Backfill with expanded clay.

Among the materials for warming the base, there is only one popular material for thermal insulation - mineral wool. When filled with water, each type of water will lose its thermal insulation properties.

And although it not only perfectly absorbs, but also easily gives off moisture, for the base it will not be possible to create conditions for its weathering.

Technique of insulation strip foundation Each type of insulation has certain characteristics that will dictate the methods of its application.


Non-removable formwork

This is the only method for insulation that is possible only at the stage of erection of a monolithic strip-type foundation ...

In fact, this technology can be called "2 in 1", when the formwork from materials for thermal insulation remains as a structural part at the end of construction. At the same time, permanent formwork will solve 2 problems at once - how to make the base of the house inside and outside warmer.Structurally, there are two types - shield and block. When pouring a strip-type foundation, shields are used, and the blocks have walls, and also transverse lintels of large width, and this significantly reduces the strength of the reinforced concrete base. Such formwork is made from various materials, but most often the base is insulated from the outside using expanded polystyrene (simple or extruded).

In addition to the standard technology, there is also a combined one, when the plates do not need to be connected to each other, but are attached to the removable formwork.

After backfilling of the sinus near the underground part of the base is done, a trough is prepared for the blind area from the compacted earth. And then we do everything according to a simple scheme - crushed stone, sand, a film for waterproofing, insulation (expanded polystyrene plates), formwork, reinforcement and concrete pouring. Together with the latter, you can use a tile for sidewalks or gravel, then the insulation of the blind area, as an element of the main work, is mandatory.

Insulation with expanded polystyrene

In contrast to the above-described method, an already existing base is insulated, and therefore there is only an external type of insulation.

Work is carried out during the construction process, and even during the reconstruction / repair work of the house. The most difficult part is to carry out the work during the repair. Before insulating the base of the house from the street side, it is required to dig up and clear the tape from the ground to the heel. Further, the steps go in the following sequence:

  1. Make waterproofing - first you should apply a bituminous primer, and then stick or solder strips of rolled material with overlapping seams to the top from below.

Please note that it is better not to use bitumen-type mastics together with sheet-type heaters - they are very fluid and do not provide reliable fastening of the plates to the glue solution.

  1. Next, you need to prepare an adhesive based on cement, and through it you can fix the slabs to the base. In the part of the above-ground type, additional fixation with dowels is not at all necessary - only on the base. The direct method of fixing the plates by means of mechanical fasteners without glue solution is unacceptable - the adhesive composition can serve as a gasket between bitumen and expanded polystyrene, which is a negative environment for polymers.
  2. After backfilling and making the blind area, the basement room is finished with a layer of adhesive, and reinforced with fiberglass mesh, and also plastered or tiled.

Consider another method of insulating the foundation from the outside.

Insulation with polyurethane foam (sprayed)

Insulating the foundation of a house from the outside is the best method of saving the foundation of a building Among all polymer-type heaters, sprayed polyurethane foam is the most expensive type. Its advantage is that the thermal insulation layer has no seams, and the foamed polyurethane has excellent adhesion to all types of building materials. application of polyurethane foam to a cleaned surface from dirt is extremely fast.There are a couple of types of materials - two-component and one-component. In the first case, professional equipment is required, and its work will consist in supplying two components under pressure to the working head, where mixing and foaming will take place.

One-component material is released in aerosol liter cans, and even a beginner can handle them correctly. But this technology is great for a small front of work, or when you need to apply a small layer with a thickness of up to 20 mm.

If the ground is dry, then the level of the top water is low and competent drainage works have been performed, then the waterproofing of the foundation and the basement can be omitted - there are no seams, and the water absorption of the solidified polyurethane foam is small (no more than 2%). When decorating the basement with plaster, reinforcement is not required - there are no joints, like foam plates, which means there are no prerequisites for cracks. In addition to cost, polyurethane foam has a small drawback, which is a consequence of one of the advantages - excellent adhesion.

When carrying out work on the insulation of the basement, it is required to protect the walls that have a finish (or do not require it) - this is much easier than peeling off the hardened foam.

Warming with expanded clay

Recently, in order to insulate the foundation, such bulk material is rarely used. Its use is limited by two factors - rather high, in comparison with polymer types of insulation, thermal conductivity and water absorption. The first indicator will range from 8 to 20% of the total. At the same time, such water absorption is characteristic of "fresh" expanded clay - after a while it will become higher.

By comparison, in simple foam it is not more than 4%. For this reason, waterproofing of the foundation is required, and only a layer of insulation. it is impossible to ensure ideal tightness of expanded clay, and it will dry out underground, wrapped in a film, for a long time - its use is not recommended in conditions of a high rise in groundwater in the spring season.

Thermal conductivity does not yet meet modern requirements for thermal protection of buildings - from 0.07 to 0.

18 (W / s * O C) against an indicator of 0.02 to 0.04 for polyurethane foam, for PPS / EPPS 0.03-0. 04.

For this reason, the recommended thickness of bulk thermal insulation for our mid-latitudes will be in the range from 0.4 to 0.6 meters. The insulation scheme will look like this:

  1. It is required to dig a trench of the estimated width (or it is important to clear the cavity of the pit) to the very heel of the base.
  2. Next, it is required to lay a waterproofing film over the entire area of ​​the trench - foundation, bottom and wall.

  3. After that, the expanded clay is poured and leveled.
  4. Cover the top with plastic.
  5. Add a layer of sand.
  6. Make a blind area.

The advantage of expanded clay is its low cost and environmental friendliness.

But taking into account the waterproofing and the huge amount of materials, the cost of the work in the end turns out to be not so low.In addition, the base will need to be insulated using one of the above methods.


The selection of a specific material and how exactly to insulate the foundation of the house will depend on most conditions - construction or repair work, wet or dry soils, frost penetration depth and heaving, budget and scope of work, depth and structure of laying the foundation. For this reason, such a task should be solved exclusively by professionals.