How to insulate the foundation of a house?

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Laying foundations is only half of the success. The second half is proper protection against dampness. Why is it worth insulating foundations?

Important foundation insulation

If foundationsdo not have proper insulation, they are exposed to the penetration of moisture or water from the ground – which leads to permanent dampness, and in consequence to corrosion of the foundations.

Permanent dampness of foundations causes also reduction of their thermal insulation and dampness of first floor walls – at first it is peeling of paint and later appearance of fungi and moulds on the wall.

The insulation can be omitted if the foundations are made of waterproof concrete. However, it is always worth protecting them additionally with another layer of insulation.

Horizontal foundation insulation

Capillary rise is very dangerous to foundations. It is sucking up water to the top, which got to the foundation – this causes dampness of the first floor of the building. You can protect the first floor of the building from dampness by applying damp insulation of the foundations.

The horizontal insulation of foundations is placed in two places – between the strip footing and the wall of foundations as well as in the junction of the foundation wall with external walls of the building (it is installed at the height of 15-30 cm above the ground).

While insulating horizontal foundations, one should remember that the insulation cannot be located below the level of floor waterproofing.

Vertical insulation

Vertical insulation of foundations is equally important as horizontal one. It is laid on the surface of the foundation walls. Vertical insulation is to provide a stop before penetrating the wall:

  • moisture,
  • rainwater,
  • ground water.

This type of insulation must always fit tightly against the wall. If the foundations are not level, they must be levelled with a thin layer of cement mortar. From the outside, the foundations must be protected against mechanical damage.

Types of insulation of foundation walls

Depending on your needs and site conditions, choose one of three types of insulation:

  • light damp insulation– provides protection against rainwater and natural dampness of soil. This type of insulation is used on permeable grounds, i.e. sands and gravels, and when the water level is clearly below the foundations. It is made only on the outside of the foundation, from bituminous mass.
  • average waterproofing– is recommended for securing foundations against rainwater, which is below the foundation, but the ground is impermeable. Such insulation must be made of tar paper, KMB mass and cement slurry.
  • heavy waterproofing- is used when it is necessary to protect the foundations against pressure water. This type of insulation is characterized by high mechanical strength. It is made of torch-on membrane, KMB mass, self-adhesive foil and cement slurry.


Materials used for foundations insulation


Material used for horizontal and vertical insulation, has a very high mechanical strength, is resistant to chemical agents and UV rays. For the insulation is used roofing paper:

  • heat-welded membrane,
  • modified with SBS elastomer,
  • on a matrix of polyester fibres.

The membrane is laid on the foundation in one or two layers. Thermal-weldable membranes are laid using a special heater.

Foundation foils

Foil for horizontal insulation of foundations is made of PVC or polyethylene. This material requires a smooth and even foundation – sharp edges may damage the membrane.

Bituminous masses

This material is perfect for light damp insulation and medium water insulation. The most popular bituminous compounds are:

  • adhesives,
  • asphaltic masses,
  • asphaltic and resinous,
  • asphalt-rubber,
  • asphalt-polymer.

This material is applied to the foundation with a brush, brush or trowel- when dry it forms a tight coating.

KMB masses

Currently the best material on the market for vertical waterproofing insulation – thick layer.

Sealing slurries

This material can be used for any type of insulation. It is a fine-grained cement mortar modified with cement resins.

Pressed foils

This type of material is used to protect the insulation from mechanical damage and as an element of foundation drainage.

External insulation of foundations is becoming a standard not only in newly built houses.

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