With the development of energy-saving demands, increasing emphasis is attached to the thermal insulation of building parts under terrain level such as foundation bodies, whether they are strip foundations or foundation slabs under the entire building. Apart from reducing downward thermal flows, also satisfaction of the requirements related to thermal comfort and the protection of buildings is important. Floor temperatures may not differ from the air temperature of the tempered space by more than +/-3°C, and vapour condensation is not allowed either on the floor surface or in the floor structure! The RAVATHERM XPS thermal insulation proves excellent even in this place exposed to moisture.
For long-lasting and efficient operation, the following requirements are to be considered when designing and selecting thermal insulation materials 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 understructures:
- protection of the insulation against ground moisture and ground water in the period of construction and soil backfill
- the thermal insulation boards do not require any additional protection
- despite the persistent effect of soil moisture, there is no modifying factor increasing the U value
- no damage caused by soil backfill and compaction
- no ground water contamination
- several decades of reference documented by independent institutions
Strip foundations form a close structural unit with building socles, so they require thermal insulation as potential linear thermal bridges. Subject to energy sizing, thermal insulation is required at least on the outer side of or next to strip foundations, but, time after time, also on the inner side (soil, backfill). In cases of small foundation depth, the XPS thermal insulation placed under the reinforced concrete foundation slab will act not only as floor thermal insulation, but also ensures the frost protection of terminal zones coming to be above the frost line.