The Australian housing market demands affordable, quality homes. For a potential buyer inspecting a newly-built home, the only observable measures of build quality are often cosmetic and functional – is the paint finish flawless? Do the doors close smoothly?

For a consumer, it is often not possible to see beneath the surface to judge how well the house itself was built. Proper water management is one of those qualities that is unfortunately difficult to verify. Basic tools of building science like blower doors and infrared cameras can help to see beneath the surface.

I was recently invited to test some houses being built outside Sydney with a blower door (air tightness test). From inside a room in one house (picture 1 below), nothing looks amiss. But during the test, the infrared camera indicated that one corner was colder than all the others. This means there is a leak to be uncovered.

Walking outside, I found the culprit. It had rained the week before, and it looked like at some point, water had pooled behind the house and soaked the first course of bricks outside that room (picture 3 - see the bottom row of dark bricks). The evaporating water makes that corner cold and show up under infrared and blower door. This was a brand new house, but it will rain again someday. These bricks will get wet again.


At another site nearby, I looked at a window frame from inside a house under construction, and I was not convinced that the installed water-proofing measures were going to work (picture 4 below). Looking at the drainage around the window, a builder said that the sill flashing which extended wider than the window frame would catch any water from the window sill and direct it to the weep holes in the brickwork and safely outside.

But from the picture below it seems that water is quite able to pour off the end of the sill flashing and down into the wall cavity. The builder was again convinced this was no problem, as the flashing at the damp-proof course below would catch it and direct it outside. I imagined a little cascade trickling from one flashing to the next during a heavy thunderstorm. How calming.

Along the way there, however, there is insulation placed in these cavities, and while manufacturers pledge that their products will not support mould growth, they have no intention of them being used in a water feature. Elsewhere in the same development, water had obviously soaked many of the walls under construction (picture 5). Had there been even rudimentary waterproofing on these walls, these components would not be wet at this stage.


This is not a problem unique to New South Wales. At a site outside Melbourne, the same problems were blatantly obvious. There, sarking was used to provide a modicum of weather-sealing for walls, but no flashing or tape was used to seal around windows. These gaps will not get much more attention, and tapes that were being used to seal the sarking were peeling off after only a few days. When finished, these homes will leak air and that wastes energy, but they will also leak water, and the walls will host mould, mildew, bugs, and termites.

If you're thinking “that’s fine, but clearly you don’t want to seal a house too tight,” you should banish that thought. The reason people fear sealing a house too tight is because the standard of construction is often so poor that sealing in defects would be bad for your health. Essentially, old construction was more tolerant of poor workmanship. If a house had a water leak, it was so draughty that air leaks would dry out the water leaks before they fostered mould.

Unfortunately, the rationale that we should tolerate draughty homes that are expensive and uncomfortable because we can’t figure out how to manage water correctly is weak. Our priorities should be arranged in order of risk: fix water management, then fix air sealing, then fix insulation. Again, we want to seal unintentional leaks in the building envelope completely, and then add intentional air movement with controlled ventilation. This is the only way to reliably ensure good air quality.

Competition in the business of energy-efficient construction in Australia is growing. The tolerance in the Australian market for extremely poor workmanship must diminish along with that.

  • You make some very good points Sean. Any good Building Biologist knows that moisture invasion is a potentially serious health hazard for both the occupants of the building and as you clearly illustrated, to the building itself. Windows are notorious for gathering moisture into wall cavities particularly around the lower corners and below – mould is a guaranteed outcome. Anything holding moisture against the building especially above the damp course will ultimately invade as you rightly describe in your exterior example.

    This begs the question as to why a Certificate of Occupancy issued by a totally independent experienced professional service on completion of building work is NOT a mandatory requirement in Australia. Few home buyers and especially first timers have the knowledge and expertise or the means to test or inspect sufficiently to pick up faults after completion. While independent certifiers should be picking up potential faults during construction they are so often under time/workload stress and coming from the industry usually rather sympathetic to the builder's view I suspect. Another layer adds costs up front though could save millions over the building's lifetime.

    The major problem in Australia is the basic house design and construction methods most commonly used as well as poor work standards due to less than satisfactory training and regulatory oversight. Stick frame construction most commonly used is inherently prone to problems and moisture damage particularly as well as thermally inefficient. Air tightness is difficult to achieve and may add to mould and air quality issues as experience shows.

    Cheap and Quick are the operative words for housing construction in Australia and the home owner is left to struggle with the inevitable consequences including major health effects. There are better ways to do this and far better materials and methods well tried and tested that can produce a durable healthy home.