Does airtight make sense in warm climates?

I get asked this a lot on the Coast. People hear airtight and picture a sealed box. It's not. Airtight is about control.

Control, not sealing yourself in

As I write this I'm in my airtight office with the door wide open, because it's a beautiful spring day. You can open the windows whenever you like.

Airtight decides what happens when they're shut. A leaky house breathes randomly, through gaps around windows, wall cavities and downlights. An airtight house gets its fresh air through the ventilation system: filtered, where you want it, at the rate you want.

Humidity

At Sunshine Coast Airport, average humidity in January and February is over 70%, morning and afternoon. When we cool the house, that humid air wants in. In a leaky house it's pulled through the wall cavities, hits cooler surfaces and can condense. The building code's condensation handbook says air leaking through gaps is far more critical than moisture moving through the linings. That's mould in a wall you'll never see.

For how the rest of the system works, read "Walls that dry out: wraps and membranes for a Queensland climate" and "Why an ERV alone won't fix humidity in South East Queensland".

Smoke and pollen

In bushfire smoke, Queensland Health says to stay inside with windows and doors closed, and CSIRO found tighter houses keep more smoke out. Grass pollen is a major hay fever and asthma trigger, and a Brisbane study found grass pollen levels in 2016 to 2020 were nearly three times those of the late 1990s. The F7 filters in an ERV like the Zehnder ComfoAir Q or Dantherm HCV catch pollen and fine dust, but only if the air comes through the filter and not the gaps.

Cooling

Every bit of hot, humid air that leaks in has to be cooled and dried by the air conditioner. Stop the leaks and a smaller system runs less. Add a dehumidifier like the Microwell DRY for the sticky weeks and you can run the air conditioning warmer and still feel good.

How we get there

A continuous, taped airtight layer like Pro Clima INTELLO PLUS and TESCON tapes or Proctor Wraptite SA, a blower door test before the linings go on, and mechanical ventilation. Then open the doors when the weather's good. I do.