Leaky Buildings 2.0

Most of us are familiar with leaky buildings – the perfect storm of poor design, poor cladding systems and poor workmanship, culminating in allowing rain to get in. Now we’ve moved on and have cavities, more stringent weather-tightness checks and hopefully we like eaves again. So what’s leaky buildings 2.0? If we’ve dealt to the risk of moisture coming in from the outside, where else can moisture come from?

Fixing a leaky building can be an expensive and time consuming exercise. But what about addressing moisture from the inside?
Fixing a leaky building can be an expensive and time consuming exercise. But what about addressing moisture from the inside?

Leaky Buildings 2.0

Leaky buildings 2.0 is not my term. I first heard it from Thomas van Raamsdonk of Pro Clima. Thomas was featured in episode 26.

The reality is that moisture from outside (i.e. rain), is only half the issue. There are plenty of other, significant sources of moisture from within and under the typical house. Check out the table of moisture sources on Smarter Homes and from BRANZ.

This publication from BRANZ states that the ground below a typical 150 m² house can produce up to 60 L of water per day!

Level also has a good explanation of humidity and condensation and Lois Easton has written a good article on the importance of a ground vapour barrier.

The Perfect Wall

Joseph Lstiburek (apologies for my butchering of pronunciation in the episode) is the guru of this stuff. He’s written this fantastic article on the ‘perfect wall’. I can’t say it any better than Joseph. So if you want to avoid leaky buildings 2.0, I suggest you head over to Building Science Corporation and read his article.

Model it. Or find someone who can.

WUFI is a powerful software package for modelling the likely flow of moisture in a wall or building component. But a good designer with a basic understanding of a psychrometric chart will also be able to do a risk assessment of interstitial condensation. If your designer doesn’t know how to find out if the dew point might occur somewhere with your wall for the climate your building in, then find someone who can.

PsychrometricChart.SeaLevel.SI” by ArthurOgawaOwn work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

  • Joe described the Perfect Wall, and everyone mistakenly took it that he only meant a wood framed wall, wrong. If you carefully apply the principles to a generic wall on a blackboard you get 4 lines, why Passive goes over that amount by as many as 3-4 times is mind boggling. It could be that wood is not the most economical building envelope solution, especially when you consider the average lifespan of the wood framed home is 32-34 years.
    Every layer costs time and money, so don’t need.

    Building a thousands of dollars home, then with wisdom place a 15 year Asphalt Roof on it could also be another reason for that average, who loves costly repairs, yes I know its a free world. More layers make it harder to find and fix problems, you’re the boss.

    • mcutlerwelsh

      Yes, layers can be confusing when you’re not used to them, and there’s more to go wrong potentially. I think that’s why it’s important to get your overall design strategy right first.