Today I want to discuss a really important subject:
The Invisible Enemy
In October I attended the Building Physics Forum in Melbourne. Over 2 days experts from all over the world spoke about healthy and energy efficient homes and the danger of condensation and mould.
There was lots of theory and science behind it. But:
We spoke mainly about THE INVISIBLE ENEMY: AIR – LEAKAGE.
And how it can lead to construction damage and mould.
- Water leaks get attention fast
- Air-leakage gets attention NEVER
- Air—leakage damage (mould) will always blame water leakage
So why is air leakage so dangerous?
Let’s start at the beginning. What most people don’t know is that we humans produce a LOT of water.
A 2-person household produces about 8 Litres of water per day.
And that does not include other daily household activities like drying clothes inside.
This moisture must go somewhere. Most Australian homes, even those with a 6-star rating (Australian minimum), are so draughty and have so many air-leaks, that water vapour can travel relatively easily in and out of the house.
But having said this, no matter how draughty a home is, if the moisture content gets too high, water will start forming on the coldest surfaces. And if you have air leakage, air and its water content can travel through the building structure. If this keeps reoccurring and depending on where the water forms, it can lead to structural damage (eg. rotting timber) and/or mould growth.
Even though the more air-tight our homes are, the more critical it is to remove the humidity from the house. There is a lot of proof and papers even from the 19th century, where homes were infested with mould due to poor ventilation. And back then some of those houses didn’t even have proper windows. So, this is not a new problem.
By now, most industrial countries have strict regulations in place to control and minimise air-leakage. Except for one: AUSTRALIA.
Air-leakage is tested via a Blower-Door test. It measures airflow between building zones, to test ductwork airtightness and to help physically locate air leakage sites in the building envelope.
The test result will be a number, that tells how many air-changes per hour your house has. For instance, 1 ACH (Air-Change per Hour) means in one hour the entire air inside your house is exchanged (can escape through little gaps and holes).
The Passive House Standard does require an airtightness of 0.6 ACH. In comparison to that, the latest NCC in Australia (National Construction Code) has an allowance for air leakage of 10 ACH. However, there is no mandatory testing required just yet.
Recently a study was done in Australia where they tested 125 newly constructed homes with a minimum 6-star rating. And the shocking outcome was an average of 15.4 ACH. This is equal to several large holes in each wall.
It truly was a shocking outcome. Australia has by far the worst performing homes in all industrial countries. Even the worst homes in America test at about 7 ACH.
This poses all sorts of issues. Not only are homes really draughty, and hence don’t feel comfortable with 15.4 ACH. They also require a lot of mechanical heating and cooling to keep the indoor temperature at an acceptable level.
In my next blog post I will be talking more about our current regulations in Australia, compared to what is going on overseas and the implications on building more air tight homes and how to overcome mould issues.