Rainscreen cladding

Fibre Reinforced Facade Encyclopedia: Design and detailing

Rainscreen cladding is the outer skin of a rainscreen facade: the panels that face the weather, the rails and brackets that carry them, and the joints between them. The principle behind it, a drained and back-ventilated cavity with the waterproof line on the backing wall, and the pressure-equalised variant of that principle, are set out on the rainscreen page. This page is about what the build-up consists of, how deep it has to be, and what goes wrong.

At a glance

The build-up, layer by layer

From the inside out: the backing wall, in concrete, blockwork or light steel studs with external sheathing; the weather barrier membrane on its outer face; the brackets passing through the insulation to the structure; the insulation cut tight around them; the clear drained and ventilated cavity; the cavity barriers interrupting it at defined lines; the rails; and the panel.

Each layer has to be continuous in its own right, and each is interrupted by the next. The membrane and the insulation are punctured by brackets. The cavity is interrupted by barriers and flashings. The panel is interrupted by joints. Rainscreen detailing is almost entirely about resolving those interruptions, which is why the sections matter more than the elevations.

The load path is worth stating plainly: the panel carries wind and its own weight to its fixings, the fixings to the rails, the rails to the brackets, the brackets to the structure. Rails and brackets are the substructure; the connection from panel to rail is the panel fixing system. They are designed together and are not the same thing.

Cavity depth and what has to fit in it

The working rule is a 25 mm minimum clear cavity behind the panel, with 25 to 50 mm the normal range. Clear means clear: measured from the back of the panel to the face of the insulation or of any obstruction, not to the backing wall. A 50 mm cavity containing a 40 mm bracket flange every 600 mm is not a 50 mm cavity at that point.

The cavity has to drain, with a continuous downward path to a flashing that discharges outward at the base and at every interruption; ventilate, with open area at the base and head of each compartment; and give the installer room to reach a fixing. A cavity that drains on paper but cannot be worked in gets built wider on site, or built as drawn and fixed badly.

The total wall zone follows. With 140 mm of mineral wool, a 40 mm clear cavity and a 60 mm rail and bracket assembly, a 20 mm panel face sits about 260 mm off the backing wall. That dimension drives the slab edge, window setting out, soffits and parapets, so agree it early.

Open joints and tolerance

An open-jointed rainscreen leaves the panel joints unsealed. That suits moulded and thick panels, and removes the maintenance liability of a sealant line across a whole elevation. The price is that the joint is visible, so what sits behind it has to be deliberate: a black-coated baffle, a returned panel edge or a purpose-made joint profile. An open joint looking into a bright rail and a silver bracket is a detailing failure that shows up on the first clear afternoon.

Joint width is a tolerance calculation, not an aesthetic choice. It has to absorb the panel manufacturing tolerance, the substructure setting out tolerance, the accumulated tolerance across a run, and the thermal and moisture movement of the panel. GRC moves with moisture as well as temperature; FRP has a higher thermal expansion coefficient than concrete; metal moves more again. A 2.4 metre panel with 8 mm of combined tolerance and 3 mm of movement cannot live in a 10 mm nominal joint held to plus or minus 2 mm.

In practice 8 to 12 mm suits small panels and 12 to 20 mm suits panels of 2 to 4 metres, with designated movement joints at intervals set by the material and the fixing layout. Nominate the nominal width, the permitted variation and the accumulated tolerance separately, and require setting out to a facade grid.

Insulation and cavity barriers

Where the external wall must be non-combustible, the insulation is normally stone or mineral wool: dimensionally stable, vapour open and non-combustible when tested. It has to be mechanically fixed with retaining washers rather than friction fitted, because a slumped slab leaves a thermal gap and can block the cavity. Use a tissue faced or black faced board where cavity air speeds are high or the insulation is visible through an open joint.

Cavity barriers close the cavity as a fire path, horizontally at floor lines and vertically at compartment lines and around openings, to the building fire strategy. Because the cavity must keep draining and ventilating in service, open-state intumescent barriers are used where a solid barrier would dam it: they sit with a defined open gap and expand to close under heat. They must go in before the panels close the cavity, compressed to the stated installed thickness, and continuous around every corner and penetration. A barrier with a 30 mm gap at a bracket is not a barrier.

The panel material is separately subject to the external wall fire provisions. Under NCC 2022 (check the edition adopted in your jurisdiction), external walls of Type A and Type B construction must be non-combustible under the Deemed-to-Satisfy route, which a GRC panel tested to AS 1530.1 can satisfy, or the complete system must be tested to AS 5113 as a Performance Solution.

What goes wrong

• The cavity is blocked. Insulation bulges, mortar snots sit on a flashing, or a bracket flange spans the cavity. Water dams and the drainage design is defeated.
• Cavity barriers installed after the panels, lapped rather than compressed, or omitted. This is the most common and most serious fire defect in installed rainscreens.
• The membrane lapped the wrong way, or bracket fixings puncturing it without a sealed washer or patch. Every penetration is a leak path in the only waterproof layer in the wall.
• No flashing over openings, at floor line interruptions or at the base, so water reaches the cavity and has nowhere to go but inward.
• Joint widths taken from a rendering. Panels bind on the first hot afternoon, or the joints open unevenly and the elevation reads crooked.
• Open joints with nothing behind them, so fixings, rails and insulation face are all visible.
• Sealant applied to panel joints on site to stop a leak, converting a drained facade into a trapped one and moving the failure somewhere less visible.
• Aluminium rails in direct contact with stainless or galvanised steel without isolation, or carbon steel fixings in a coastal facade. Bimetallic corrosion is slow, invisible and structural.
• Insulation left unretained behind a panel line that will never be opened again.

Standards and references

• NCC 2022 Volume One, C2D10 non-combustible building elements, C1V3, and the cavity barrier provisions
• AS 1530.1 combustibility, AS 5113 full-scale external wall fire test, AS 5637.1 group number
• AS 4284 Testing of building facades; AS/NZS 1170.2 Wind actions
• CWCT Standard for Systemised Building Envelopes and CWCT technical notes on rainscreen and cavity design (UK)
• NZBC E2/AS1 External moisture (New Zealand)
• AAMA 508 pressure-equalised rainscreen and AAMA 509 drained and back-ventilated rainscreen (US)
• AS 3566 and AS/NZS 2699 for fastener corrosion classification

Where this matters on a ShapeShift project

Related terms

• Rainscreen
• Open joint
• Cavity barrier
• Weather barrier
• Substructure
• Panel fixing systems
• Thermal bridging
• Flashing

Questions specifiers ask

Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.