Things to Know
Anyone involved in any kind of construction business, whether professional or personal, will know a thing or two about airtightness. Maybe they’ve only heard it referred to as air leakage or air permeability, but they’ll know that if a building doesn’t pass its airtightness test, it ain’t going on the market.You might think that’s all you need to know, what else could be important? Well, the environmental impact inefficient buildings have on the ozone layer and the greater natural world goes without saying (although it really shouldn’t). But on top of this, there are other factors involved which could affect the building, the lungs of whoever will be living in that building, and the wallet of that person too — or perhaps even yours. So, without further ado, here are 5 things you should know — for the sake of wallets, lungs and penguins.
Avoid air leakage
Any warm, moist air from the inside that finds its way through the building’s external envelope can cause condensation. Specifically, this is interstitial condensation (interstitial means the space between objects or structures), which happens when this warm air reaches a cold surface like the outside of the hole or a cold water pipe. This can lead to fabric decay, which is never easy to sort out and can prove costly in more ways than one (remember the wallet and the lungs?). Increase the air tightness of your build and it significantly reduces the chances of fabric decay happening.
When detailing the air barrier, which means the materials designed/constructed to control airflow between a conditioned space and an unconditioned space, it’s crucial to ensure this is on the warm side of the insulation. If you read the previous paragraph you’ll be able to tell me why. Oh alright then, I’ll just tell you again. This is to avoid condensation in the fabric caused by warm, moist air hitting a cold surface.
If you ‘achieve' an air tightness figure of 10 m3/(h.m2) @ 50Pa, this is roughly the equivalent of having a hole the same size as a 20p coin in every m2 of envelope area. When you consider how many square metres are in the entire building envelope, it’s a pretty worrying thought. So, if you don’t want a sieve for a house, you need to be aiming for a much lower figure than this to achieve proper energy efficiency.
It’s not really possible for a building to be too airtight. The less air leakage, the better. However, a building can be under ventilated, and this is a common mistake that people make — to focus solely on air tightness. It’s great ensuring that you have a nice, sealed, efficient building with almost no air leakage, but you also have to think that people need to breathe. Ensuring enough air circulates the building, in a controlled way, is essential in preventing the build up of moisture and airborne pollutants which come as a result of occupying or living in a space.
build at a time
You’ve just had the results of your air tightness test and it’s a pass, well done! It may have been straightforward, but chances are it gave you a bit of a headache at least once in the process. To make things easier on your next projects, we highly recommend having an air leakage audit, even though you’ve passed. This will allow you to see where the building is leaking so you can improve on these bits in your next building endeavour.