Fibre Reinforced Facade Encyclopedia: Design and detailing
A rainscreen is a facade system in which the outer cladding is separated from the inner wall by a cavity that is drained and ventilated. The cladding sheds most of the rain; whatever gets past it drains down the cavity and out; the inner wall carries a continuous weather barrier that keeps the building dry. Almost every lightweight panel facade, in GRC, FRP, terracotta, metal or fibre cement, is built this way.
Rainscreen facades work by accepting that the outer skin will leak. The joints are open or lightly sealed, the cavity behind is 25 to 50 mm deep and vented top and bottom, and the membrane on the backing wall is the real waterproof line.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Outer skin | GRC, FRP, terracotta, metal, fibre cement, stone, timber | Sheds rain, provides the appearance |
| Cavity | 25 to 50 mm typical; drained and ventilated | Must be interrupted by cavity barriers in taller buildings |
| Weather barrier | Membrane or sarking on the backing wall | The waterproof line |
| Joints | Open, baffled or sealed | Open joints suit thick or moulded panels |
| Substructure | Aluminium or steel rails and brackets | Sized for panel weight and wind load |
| Pressure-equalised variant | Compartmented cavity with vents sized to equalise pressure | Reduces water driven through joints |
| Fire | Reaction-to-fire class of every layer; cavity barriers; full-scale test for tall buildings | Cavity is a fire path unless barriered |
How the water is managed
A sealed facade fails when its seals fail, and all seals fail. A rainscreen is designed so that failure of the outer skin does not matter. Rain hits the panel and runs off. Some enters the joints, driven by wind pressure and capillary action. It meets the cavity, where the pressure drops and the water falls to a flashing that directs it out at the base or at each floor. Air moving through the cavity dries what remains. The membrane on the backing wall sees only occasional wetting and is never the primary defence.
A pressure-equalised rainscreen goes further: the cavity is divided into compartments with vents sized so that the air pressure behind the panel matches the pressure in front of it, which removes the force that drives water through the joints in the first place.
Why lightweight panels suit it
The rainscreen cladding carries no load but its own weight and the wind, so the material only needs to be stiff, durable and attractive. That is the brief thin composites are made for. A GRC or FRP rainscreen panel at 20 to 50 kg per square metre hangs from light rails and small brackets, which in turn means fewer and smaller thermal bridges through the insulation, faster installation and less demand on the structure. Open-jointed rainscreens also suit moulded panels whose edges can be returned to hide the cavity.
Fire in the cavity
The cavity that drains water also channels fire. In the cladding fires of the 2010s, flames spread up the cavity behind combustible panels and insulation far faster than they could have across the face. Every rainscreen on a building above modest height now needs cavity barriers, either intumescent open-state barriers that allow drainage and close under heat or solid barriers at floor lines and around openings, and the panel, insulation and membrane are all subject to reaction-to-fire requirements. On Type A and B buildings in Australia the panel must be non-combustible under Deemed-to-Satisfy or the whole system must be tested to AS 5113 for a Performance Solution.
Design checklist
- Cavity depth and venting: 25 mm minimum clear, vented at base, head and at floor flashings
- Drainage path: continuous, with flashings at every horizontal interruption
- Weather barrier: continuous, lapped and sealed, compatible with the insulation
- Cavity barriers: located to the fire strategy, open-state where drainage must continue
- Substructure: designed for panel weight, wind pressure and suction, thermal movement and structural tolerance
- Joints: width set by panel size and expansion coefficient; open joints with a baffle or a returned edge
- Panel material: reaction-to-fire class appropriate to building type and height
Standards and references
- CWCT Standard for Systemised Building Envelopes (UK); CWCT Technical Note on rainscreen design
- AS/NZS 4284 Testing of building facades (Australia); AS/NZS 1170.2 (wind actions)
- NZBC E2/AS1 (external moisture, New Zealand)
- AAMA 508 and AAMA 509 (pressure-equalised and drained rainscreen tests, US)
- NCC 2022 Volume One C2D10, C1V3, and Specification 5 (cavity barriers) (check the edition adopted in your jurisdiction)
Where this matters on a ShapeShift project
One Sydney Harbour, Barangaroo: A high rise residential tower where moulded panels are hung clear of the wall behind them, so that the cavity and the wall line carry the weathering function rather than the joint between panels.
Related terms
Questions specifiers ask
Is a rainscreen waterproof?
The outer skin is not, and is not meant to be. The system is waterproof because the cavity drains what passes the panels and the membrane on the backing wall stops the rest.
How deep should the cavity be?
At least 25 mm clear behind the panel, commonly 25 to 50 mm, vented at the base and head and drained at every floor flashing.
Do rainscreens need cavity barriers?
On buildings above modest height, yes. The cavity is a fire path and must be interrupted at floor lines and around openings, using open-state barriers where drainage must continue.
Which materials are used for rainscreen panels?
GRC, FRP, terracotta, aluminium and steel sheet, fibre cement, stone and treated timber. The choice is driven by weight, geometry, finish and fire class.
What is a pressure-equalised rainscreen?
A rainscreen whose cavity is compartmented and vented so the pressure behind the panel equals the pressure in front, removing the driving force that pushes water through joints.
Designing a rainscreen in moulded panels? ShapeShell-RC and RT are supplied with engineered fixing systems for open-jointed rainscreen installation. See ShapeShell fixing systems
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.