The Do’s & Don’ts of Airtight Homes

There can be skepticism about airtight homes… I’m not sure why! It’s likely for the same reason people used to be skeptical about double glazed windows… How ridiculous! I remember a homeowner many moons ago telling me he didn’t like double glazing because –  “Once a home heats up you can’t cool it down with double glazed windows!”  Perhaps he’d never heard of opening them! Anyhow, I feel there can be much the same perception around the airtightness of our homes. There’s a concern that an airtight home can cause condensation, moisture and mold… Well yes, when an airtight home isn’t built correctly this can occur. Although, I assure you, condensation, moisture and mold is MUCH more common in leaky homes than airtight homes. If you’ve been following along on this short series of Energy Efficient Homes you’ll know by now the 3 key elements – Insulation, Airtightness & Orientation must be applied together for best results.   Below are some tips, benefits and things to watch out for with an airtight home. 1. You MUST NOT create an airtight home without a continuous layer of insulation. Frank Sinatra said it best… “You can’t have one without the other” or your home will have these major problems the critics are talking about. If you’re motivated for a high-performing home (who isn’t), you need both airtightness and thermal insulation in sync.

• Opting for airtightness without insulation will be a terrible disaster and you run the risk of condensation build up. Of course because of your beautiful airtight layer the condensation will be trapped in the home, and the anti-airtightness nags will say “I told you so’. 
• On the other hand, if you focus purely on that gorgeous, continuous insulation layer without an appropriate airtightness layer your home is sure to stay drafty. 

2. Build tight & Ventilate right! We all need oxygen to breathe and living in a completely airtight home without the appropriate ventilation seems like a bad idea. And, it can be… But, there’s a solution!

• The general consensus for an airtight home with under 5 ACH (Air Changes per Hour) will require a HRV (Heat Recovery Ventilation system) and can be beneficial between 5-10 ACH. – I must agree.
• A HRV constantly filters air throughout the home, removing pollutants and humidity while transferring heat throughout the home ensuring a comfortable and controlled temperature throughout the home year round. 

3. Ensure your airtight layer is also ‘vapour permeable’. A correctly applied vapour permeable airtightness layer will bulletproof your home’s structure enabling it to last for centuries. Your home can have an airtight layer that is also breathable or vapour permeable. This is a key element of any healthy home.

• An airtight layer needs to enable moisture to travel through it. This will ensure there is no build up of moisture within your home’s wall structure. It is particularly important for us Melbournians that this layer is on the external layer of your building.
• There’s a difference between a water control layer (which your airtight layer should be) and a vapour control layer. We don’t want a vapour control layer, we need to ensure vapour is able to travel through your wall system to avoid any problematic condensation build up.

We now know to have an optimum performing home we need;

1. a continuous insulation layer, 
2. correctly applied airtightness layer that is also vapour permeable
3. and, if you’re aiming for 5 ACH or lower you should opt for a HRV system. 

Stay tuned for the last component of an energy efficient home, orientation. – Put more simply, design!