What is compression-resistant insulation?
Compression-resistant insulation is insulation that can carry sustained compressive load without significant deformation, for example the weight of a floor, a roof finish or a green roof. Its compressive strength is given in kPa or N/mm² and decides where it can be used.
How is compressive strength tested?
It is determined by a standard test in which the insulation is compressed to 10% deformation. The corresponding stress is the compressive strength. A distinction is normally drawn between:
- Short-term compressive strength — under rapid loading
- Long-term compressive strength (creep) — across the service life
- Layered load capacity — when insulation is installed in multiple layers
Common materials and typical values:
- EPS 100 to EPS 300 — 100 to 300 kPa, floor and roof insulation
- XPS — 300 to 700 kPa, heavily loaded floors and basement walls
- PIR/PUR — 120 to 175 kPa standard, higher grades available
- Cellular glass — up to 1600 kPa, very high strength
- Compression-grade mineral wool — usually 60 to 80 kPa, for flat roofs
Application
- Floor insulation — under screeds and in ground-floor slabs
- Flat roofs — under ballast, paving or green roofs
- Basement walls and slabs — XPS or cellular glass in contact with ground
- Parking decks and terraces — heavy load from vehicles or paving
- Frost skirts — compression-resistant insulation at slab edges
Points of attention
- Choose a product with adequate long-term strength, not only short-term
- Butt boards tightly to avoid thermal bridges and settlement
- Avoid point loads on softer insulation
- Consider combined heat and compressive load
- Compression-resistant insulation costs more per cubic metre — use it where needed
Related terms
- Insulation
- Sub-floor insulation
- PIR
- Roof element
- Slab insulation
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