Frost Insulation

Frost insulation is the protection of a building's foundations and yard structures from frost heave by preventing the ground beneath and around them from freezing. In Finland, where the frost line can extend 1.5 to 2.5 meters deep depending on the region, frost insulation is a fundamental requirement for all building foundations, paved surfaces, and underground piping systems.

Frost heave occurs when water in the soil freezes and expands, generating enormous forces that can lift and crack foundations, buckle paving, rupture pipes, and damage other ground-level structures. The risk is greatest in clay and silt soils that retain water, while well-draining sandy and gravelly soils are less susceptible. Frost insulation works by keeping the ground beneath the insulated area above freezing temperature.

Frost insulation is typically done with extruded polystyrene (XPS) or expanded polystyrene (EPS) insulation boards installed horizontally below grade along the foundation perimeter and beneath slab-on-grade floors. The insulation extends outward from the foundation wall, creating a "thermal skirt" that protects the soil beneath from freezing. The required thickness and extent depends on the geographic location and the foundation type.

Inadequate or deteriorated frost insulation can cause foundation cracking, door and window frame distortion, floor surface cracking, and damage to paving and deck foundations. If you notice new cracks in your foundation, doors that suddenly stick or won't close, or paving that has heaved unevenly, frost damage may be the cause. A building professional can assess the frost insulation and recommend improvements.