A rainscreen wall holds the cladding off the weather barrier on a cavity of roughly 10 to 25 millimetres. It costs a little more than fixing the siding flat, and it is the difference between a wall that dries and a wall that stays wet.

Drainage

Water that gets past the cladding — wind-driven rain, a failed joint, a splash at the base — runs down the back of the cladding instead of into the sheathing. The cavity gives it a path to the base flashing and out through the weeps.

Drying

The cavity lets air move behind the cladding, which carries moisture out of the assembly. A wall that cannot dry stores every bit of water that gets in.

Pressure equalisation

A vented cavity lets the pressure either side of the cladding equalise, so wind does not push water through every gap in the surface.

The three ways it stops working

  • The base is blocked — mortar, offcuts or cladding run past the flashing.

  • The cavity is bridged — a fixing, a batten or a bead that touches both faces.

  • The top is sealed — no vent at the head, so no air movement and no drying.

None of these is visible from the ground, which is why they are worth asking about before the cladding goes on.