Insulating the foundation – what should be kept in mind?

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Whether the building has a basement or not, its foundations should be insulated. Even when the other materials have good insulation parameters. This will significantly reduce the amount of energy used to provide heat in the property.

Internal or external insulation?

One of the key decisions when designing a foundation is whether to put insulation on the inside or outside of the basement wall. In terms of energy consumption, there is not that much difference between the two varieties if the same layer of wall insulation is used on both sides. The discrepancy appears in the cost of installation, ease of application, appearance, as well as other technical issues. 

Insulation on the outside

A rigid layer placed on the outside of a concrete surface or masonry basement wall has a certain advantage over the interior variety. It provides continuous insulation without thermal bridges, and protects and maintains the waterproofing and structural wall at moderate temperatures. It also minimizes condensation problems. It also does not reduce the interior surface area of the basement floor.

On the other hand, the disadvantage is that the exterior insulation on the wall can provide a pathway for pests. Therefore, it is recommended to use a special protective coating that will prevent physical damage and degradation of the surface covered with insulation. 

To avoid this, it is recommended to use, for example, impregnated plywood or membrane material. Oil paint, polyethylene or vinyl wallpaper should not be used as an interior finish, as they can block the natural drying of moisture.

Insulation on the inside

This type of insulation is a cheaper option. The most common is rigid foam panels or spray foam. The first variety consists of a panel of expanded or extruded polystyrene foam, which are applied to the entire foundation wall. 

Spray foam application, on the other hand, is made not only on the wall, but also up to the level of the tie beam, to the appropriate thickness. As with the exterior variety, the interior insulation must not be supplemented by the use of means such as polyethylene, vinyl wallpaper or oil paint, which impede the drainage of moisture.

What issues to pay attention to?

If possible, seek more information about the soil and water conditions on the plot. Residents of properties on nearby plots may be able to help with this. It’s worth finding out about the frequency of basement flooding, the height of water in wells and insulation problems that arose during the construction of the house.

There are also issues related to securing excavations, especially those with vertical walls. One overlooked aspect is how often vehicles pass near the site or if heavy construction materials are stored nearby. This can compromise the stability of the excavation slopes.

It is also important to pay attention to the contractor’s team to ensure that the foundation is properly leveled, that the foundation is properly compacted to the floor, or that the damp proofing is continuous. Selecting proven and qualified professionals is an extremely important consideration when it comes to proper insulation and maintaining an efficient energy profile for the property.

main photo: Tapert

Peter Bowers

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