An air cushion roof is a roof built up from two, three or four layers of foil with air continuously blown between them. The trapped air keeps the cushion taut and at the same time provides the insulating effect. The foil is usually ETFE (ethylene tetrafluoroethylene), occasionally a coated fabric.
Each cushion sits in an aluminium edge profile carried by a steel or timber structure. A compressor maintains the slight positive pressure; that pressure is low — the cushions sit gently domed, not blown up hard — but it is needed permanently.
Why foil rather than glass?
- Weight — an ETFE cushion weighs a fraction of an equivalent glazed area, so the supporting structure can be far slimmer
- Light transmission — ETFE is highly transparent, with light transmission up to around 95 per cent, and it also passes UV light, which makes it suitable over planting
- Freedom of form — almost any curved or irregular shape can be spanned
- Self-cleaning — the surface is extremely dirt-repellent and rain washes it clean
- Safety in failure — no glass shards fall
Where you see them
Swimming pools and leisure pools, zoos, greenhouses and horticulture, atrium roofs, rooflights and large stadium canopies.
Points to watch
- Insulation value — the U-value of a two-layer build-up is around 3 W/(m²·K), comparable with older glazing. Three or four layers improve it, but an air cushion roof is never the insulation solution for a heated house
- Permanent air supply — if the compressor fails, the cushions deflate. The system needs a reliable, usually duplicated supply of dried air, because moist air condenses inside
- Fire behaviour — ETFE melts away in a fire, which helps smoke venting, but the fire strategy has to be developed per project by a specialist
- Service life — the foil is expected to last well over twenty years; most ageing shows in the edge details and sealant joints
- Vulnerability — foil withstands hail but not sharp tools or falling objects. Maintenance requires a planned access route
- Sound — rain on foil is clearly audible in the space below
An air cushion roof is specialist work for large enclosures — not a DIY option for a veranda or conservatory.
Related terms
- Foil construction
- Roof pitch
- Overhang
- Truss
- Canopy
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