Walls that dry out: wraps and membranes for a Queensland climate

Most mould problems in new homes aren't leaks. They're moisture that gets into the wall and can't get out. In South East Queensland the moisture comes from both directions, so the wall has to be able to dry both ways.

Why SEQ is different

In winter the inside of the house is warmer and moisture wants to move outward, like in southern states. In summer it flips: hot, humid air outside and a cooled house inside push moisture inward. A foil or plastic vapour barrier on the inside, designed for a cold climate, can trap that summer moisture in the frame.

That's why we build with layers that let water vapour through where it needs to go, and stop air and liquid water.

The outside layer

A vapour-open wrap on the outside keeps rain and wind out but lets moisture escape. Pro Clima SOLITEX EXTASANA, SIGA Majvest and Proctor Wraptite SA all do this. Wraptite is self-adhered, which makes it an airtight layer too.

The inside layer

A smart, or hygrovariable, membrane changes with the conditions. When it's dry it slows vapour down; when it gets humid it opens up so the wall can dry to the inside. INTELLO PLUS and SIGA Majrex both work this way.

Tape every join, penetration and edge with the system's own tape. An untaped membrane lets moist air leak in, and air leaks carry far more moisture than diffusion does.

Framing and insulation

Use dry, seasoned timber. White cypress is naturally termite resistant, but unseasoned cypress shrinks as it dries and pulls tapes and linings apart.

Vapour-open insulation like STEICO wood fibre can take up and release moisture, which gives the wall a buffer.

For anything out of the ordinary, like a timber-lined bathroom or a wall with no cavity, ask your designer for a hygrothermal (WUFI) check before you build it.