Slab Edge Insulation (SEI)

The slab edge of a foundation can be responsible for approximately 80% of the slab’s total heat loss, with further research showing that thermal resistance does not significantly improve by fully extending the insulation under the slab or by increasing the thickness of the insulation under the slab. The reason being that, with no insulation on the perimeter foundations, most of the heat is conducted along the slab and out through the exterior face of the footing. This suggests that insulating slab edges is far more effective for preventing heat loss than insulating the underside of the slab. Extruded Polystyrene (XPS) is considered the best material for insulating the slab edge. XPS is resistant to moisture and has a higher compressive strength, making it a good option for foundations that may be subjected to high loads or in areas with high moisture levels.