Build Tight, Ventilate Right
Just because things have been done a certain way for a long time, doesn’t always mean it’s the right way. Architects, Designers and Builders are taught and trained how to do their job by those who have come before them, which in turn has created processes and standards that are rarely questioned. Occasionally, events or circumstances cause disruption and force change within the building industry as a reactive response. But, this is usually overdue – look at the asbestos case for example.
At Carland Constructions we want to take a proactive approach to building, especially when it comes to your home’s performance and ecological footprint. With continual professional development and having recently become Passive House Certified, we plan to implement new processes that challenge the status quo of our industry and improve the future of residential construction.
The floors, walls, windows and roof of a home represent a build-up of materials intended to protect and shield us from the outside. Effectively, we are trying to control the indoor environment to create an ideal level of health and comfort for the occupants. To do so, we must understand and resolve four key layers of control; water, air, vapour and thermal.
The most important layer is the water control layer - if we allow any external water to get inside, it's all over.
The second most important layer is the air control layer, as air carries a lot of water. This means we need to prevent the air from getting so cold that it condensates. If air is moving in and out without an airtightness layer, you may not see it straight away but it is causing damage to your construction - specifically the frame/structure. Having an airtight structure with a correctly ventilated membrane in place will prevent air from blowing out through leaks and transporting large amounts of moisture into the construction. When the air cools on its way out, the water in the air condensates and will remain in the construction. A 1mm gap in your airtight layer will create 360g of water left in your frame each day. To put that into perspective, that's one can of Coke per 1mm gap! This then leads to water damage, which is prevalent throughout New Zealand and Canada with their leaky house syndrome. Hot air will also move to where it is coldest, so having an airtight layer will prevent this from occurring.
The third layer is the vapour barrier. This allows any water that is stuck inside to move back outside and pass through the wall structure. The location of where this is placed is dependant on your climate.
The last layer is a thermal control layer. Better known to everyone as insulation, this layer restricts heat flow.
The control layers are an ordered process. If we don’t control the first three or create an airtight barrier, it doesn't matter how much insulation we put in a wall - we are going to have problems.
An easy way to understand this is to think about a very cold winter’s day. You decide to go for a hike and you put on a woollen jumper. You notice straight away that this won't keep you warm, as the single-layer will allow the wind to pass through it very easily. However, by putting on a light windbreaker jacket, you notice that you start to warm up pretty quickly. Even though the windbreaker jacket is thin, it has a huge impact and reduces air movement through your woollen jumper, helping to keep you warm. Now let's translate this into your home. We know insulation in a house works best when there is no air movement and the wind is still. So for insulation to perform at a maximum level, it needs to be protected from the wind outside to prevent air from passing through it.
Airtightness is the control of air leakage. If your home is airtight, it means there are no uncontrolled gaps in your building envelope that are allowing air to leak in or out of the building. There is a misconception that it is the air volume within your building that must be heated when you are trying to heat your home – which leads to your heater running all day. However, it only needs to be heated up once if there is no leakage in your airtightness layer. The air-only needs to be reheated if the old air is lost and new air has entered.
To measure airtightness, a fan is used to create an internal uniform pressure; the amount of air that is replaced within the defined space every hour is then recorded to determine if there are any air leakages and how big they are. To achieve Passive House standard, the building must have a rating of 0.6ACH per hour. It takes plenty of work, skill and discipline to reach this rating, which is the ultimate standard. In the UK, USA and Canada, mandatory testing is conducted on new builds where a rating of 5ACH per hour must be met as part of the requirements. Germany, Sweden and Finland take things further with a required rating of 3.5ACH.
So what about Australia? We are encouraged to achieve a rating of 10ACH, however, there is no mandatory testing or governing body to enforce this. Looking at these numbers, you can see for yourself that Australia is already quite far behind. As the standards are so low, so is the quality of the houses being built here, and anyone that argues against this is in denial. It can be argued that we don’t get the same cold temperatures that the countries mentioned above do, but what we do get is the heat and something needs to change.
To further support this, in 2016, a study was undertaken to determine the airtightness of new homes in Australia. The new homes were found to achieve an average rating of 15.4ACH. Melbourne was found to have an average of 19ACH – almost double the Australian standard. The worst part is that two of the homes studied had air change ratings over 38ACH! The airtightness of Australian homes has not been an area of concern for the building industry and this most likely won’t change until we have major problems with mould and condensation – which is inevitable.
Now, you may be sceptical about this whole movement and argue that a home should be built so that it can still breathe and provide fresh air. This is something we call uncontrolled ventilation. However, if you have ever lived in one of these old leaky homes, you will know that they are energy pigs and require a lot of power to maintain a comfortable temperature. We also know that their indoor air quality is poor and that there are higher chances of mould growing in your home - this is evident during demolition works when we find clusters of mould spores on the back of the plaster sheets. To allow the house to breathe, we install mechanical ventilation, which can control the amount of fresh air allowed in. It also removes any bad air through exhaust fans and can filter out mould spores, dust and pollen before it enters your home. Think back to the 2020 Australian bushfires, all of the smoke and ash in the air would have entered your leaky home – but with mechanical ventilation, this would have been limited or even prevented.
So whether you are designing your new home, currently renovating or thinking about renovating, remember to think about your control layers. We build an airtight home to gain control of air movement and to ventilate with control too. There are plenty of reasons to stop building leaky homes and you are now armed with some information to help make your new home healthier, higher-performing and future proof! At the end of the day, it comes down to one question – what value do you put on the health and comfort of your family?