As I had explained in Part 1, in October I attended the Building Physics Forum in Melbourne, where over 2 days experts from all over the world spoke about healthy and energy efficient homes and the dangers of condensation and mould.
The biggest takeaway for me was about THE INVISIBLE ENEMY: AIR – LEAKAGE.
Even though air-leakage can cause construction damage and mould, it gets little to no attention, whereas water leakage always attracts an urgent response. And most people don’t even know that air-leakage might be the reason for the mould inside their home and always blame it on water damage.
In the first part of this blog series I wrote about the general learnings from the forum. Today I want to talk more about our current regulations in Australia, compared to what is going on overseas and the implications on building more airtight homes and how to overcome mould issues.
To summarise the issue:
We humans produce a lot of vapour/ water. Just by being and breathing a 2-person household produces 8 litres of water each day. 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.
So how can we tackle this issue?
With ventilation – exchanging the humid air for fresh air. The issue here is, that the more energy efficient and air-tight a home gets (the less air can travel unhindered through the building fabric), the harder it gets just to provide enough fresh air in via opening windows.
When you have a home that isn’t that airtight. It might be enough to open you windows twice or 3 times a day. But we are talking about fully opened windows, proper cross ventilation for a few minutes. Just having an awning window open a bit won’t do it.
The difficulty here is obviously the outside temperature. Who actually opens the windows like this in the middle of winter or when it’s 40 degrees outside? No one, right?
It gets even harder, or I should rather say impossible when building an air-tight home, or at least aiming to achieve an airtight home. Let’s face it. The more gaps you have, the more heat you lose, the more money you have to spent to heat your house in winter, or cool down your house in summer… So building leaky homes is not an option at all.
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 you 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).
Even though there is no official regulation for it, experts do recommend that when you get to about 5 Air-Changes per Hour you should get some sort of mechanical ventilation and when you are getting toward 3 Air-changes per hour, they recommend an HRV (Heat recovery ventilation) unit.
Below is an image that shows how other countries compare with Australia and also what ACH is required for the Passive House Standard.
As you can see. There is a big need for improvement.
Just recently a study was done in Australia where 125 newly constructed homes were tested. They all had a minimum 6-star rating. The shocking outcome was an average of 15.4 ACH. This is equal to several large holes in each wall. Keep in mind, this was performed on new homes. Meaning old homes are much worse.
All other industrial countries have regulations in place on how air-tight a home needs to be, Australia only has guidelines. Homes should have an ACH of 10. But this number is neither tested nor enforced.
When it comes to the regulations, our current laws are comparable with what America had in 2002. Yes, 2002! Let that sink in.
Yet, we are heading down the same path as other countries did about 20 years ago, when they started building more energy efficient homes. Countries like Germany, New Zealand, Canada and America just to name a few. In the early 2000s they all changed the building regulations, demanding higher insulation levels. But, like Australia, they did not consider air-leakage and humidity build-up.
This led to a phenomenon that got later known as “Sick-Building-Syndrome”. The construction industry had implemented ways to increase the energy efficiency of the buildings, reducing heating and cooling costs. But sadly many homes were infested with mould. People started to get really sick. We are talking about asthma, allergies, skin reactions and so on. The industry struggled for a long time to find ways to rectify this situation. Many changes to the building regulations were necessary to not only build energy efficient but also healthy homes.
This means all those countries now have strict regulations for air-tightness. Blower door tests are mandatory in most countries. Mechanical ventilation and Heat Recovery Units are commonly used.
Whereas in Australia, the latest NCC (National Construction Code) has introduced optional air-tightness testing. Well, at least it’s a start.
Like I explained before, the more energy efficient and air-tight we build the warmer the houses get inside and the higher the risk of humidity and mould build up.
So, what can you take away from this?
Even when you are living in a house that is far from being airtight. Be mindful of how much water we humans produce each day. Remember to actively open your windows for proper cross ventilation to get the humidity out of the house regularly.
Mould from water build-up and air leakage does not happen overnight. Humidity can keep building up and mould can form after many years.
When you are building a new home, make sure everyone in your team is on board in making the home airtight. This means planning ahead of construction on how airtightness will be achieved. If the budget is tight and you cannot afford special air-tightness membranes, you can at least seal off plaster board and other joints in the house. Make sure all penetrations through the building envelope are sealed. Get self-closing fans and so on. Even with relatively simple measures like this you can get down to 5 Air Changes per hour.
This is not something you should leave to chance.
And, if you are serious about building an air-tight home, there is no way around using some sort of mechanical ventilation or even a heat recovery unit. It’s not just about saving on energy costs and making a return on your investment. It is also about your health. You can easily upgrade a kitchen or bathroom in 10 years, but you will never ever change the insulation, any membranes or windows.
We really should not make the same mistakes that other countries did before us. We really don’t want to end up with homes that make us sick.
If you want to know more about how to build healthy energy efficient homes and how the passive house standard can help you achieve these goals, please don’t hesitate to reach out to us.