As demand for energy-savings increases, more emphasis is being placed on the thermal insulation of below-terrain building parts such as foundation structures, whether they are strip foundations or foundation slabs under the entire building.
As well as reducing downward thermal flows, insulation also satisfies requirements for thermal comfort and for the protection of buildings.
Floor temperatures should not differ from the heated room air temperature by more than +/-3°C, and vapour condensation should be prevented, either on the floor surface or in the floor structure.
FLOORMATE™ thermal insulation is suitable even when exposed to moisture.
For long-lasting and efficient operation, the following requirements should be considered when designing and selecting thermal insulation materials that will be directly and persistently in contact with the soil:
- compressive strength (nominal value): ≥ 0.30 N/mm2 (300 kN/m2)
- compressive strength under protracted load: ≥ 0.13 N/mm2 (130 kN/m2)
- persistent water uptake by immersion (28 days): ≤ 0.7 vol.%
- persistent diffusion water uptake (28 days): ≤ 5 vol.%
- frost resistance: water uptake after 300 freeze-thaw cycles: ≤ 1 vol.%.
- reduction of compressive strength after 300 freeze-thaw cycles: ≤ 10%
Additional advantages of using XPS products for the thermal insulation of under-ground structures include:
- offering protection against ground moisture and ground water during construction and soil backfill
- no additional protection required
- no increase to the U-value even with persistent soil moisture
- no damage caused by soil backfill and compaction
- no ground water contamination
- several decades of references from independent institutions
Strip foundations form a close structural unit with building socles, so they require thermal insulation as potential linear thermal bridges.
Subject to U-value calculations, thermal insulation is required as a minimum on the outer side of, or next to, strip foundations, and is frequently also used on the inner side (soil, backfill).
In cases of shallow foundations, placing XPS thermal insulation under the reinforced concrete foundation slab will act not only as floor thermal insulation, but also ensures the frost protection of the closest surface above the frost line.