When you are designing very low-energy buildings, there are four crucial pillars you need to get right. Get these elements right and you are well on the way to a low-energy building:
- design/orientation of the building
- good insulation
- high quality doors and windows
Our Airtightness Measures
We’ve taken a number of steps to ensure that our project is as airtight as possible. As the floor and the back of the building (all the way up to the roof) is all underground, it features a number of water and damp-proofing systems that are effectively airtight (if they can prevent water coming in, they can prevent air getting out).
Then, as we’re building a green roof, the roofing system features even more layers of water and damp-proofing.
Then we have the concrete block exterior walls. In order to achieve airtightness on concrete block, you need to have a wet plaster finish. We used cement plaster which not only provided our desired finish, but also acts as another airtight layer.
When it comes to junctions – those areas between doors and walls for example, we have sealed these with tape to prevent air leakage. We have also used airtightness paint at various points throughout the project to ensure our structure is as sealed as it could possibly be.
One area where most people tend to struggle with airtightness is where services come into the building. We meticulously taped around all pipes, ducts and electric cables to ensure as little air leakage around these areas as possible.
Our goal was to reach a Passivhaus level of airtightness (which is 0.6m³/h/m²@50pa) – when our project was tested, we achieved a level of 0.62 which does class as Passivhaus standard. Phew!
Some advice for anyone looking to achieve Passivhaus standards of airtightness – in a building the size of ours, the total of all of the holes and cracks that could leak air could be no bigger than squash ball.