Draughts and Airtightness
All buildings let in air where they aren’t meant to. As part of building regulations, we must specially design in ventilation in our buildings such as trickle vents or mechanical ventilation systems to ensure we maintain fresh air in our homes, but unfortunately, there are plenty of areas of unplanned air flow too, making our homes draughty and expensive to heat.
A draught free or as it’s technically refereed to, an airtight building can have several advantages when combined with an appropriate ventilation system these include:
- Lower heating bills due to less heat loss
- Constant source of fresh preheat air
- Reduced risk of mold and rot because moisture is less likely to enter and become trapped in cavities
- Fewer draughts and therefore increased comfort
A typical 3-bedroom semi-detached home, built to the current building regulations could have a whole equivalent to the size of a small window in unplanned airflow, meaning that it’s like having a window fully open all the time, even in the depths of winter! Figure one has three different sized black squares, these indicate the whole sizes for a building regulations home, a standard Passivhaus and our project at Howe Park.
There are lots of common air leakage areas to consider these include:
- Between the frame and the wall, and even the letter box is a consideration.
- Floor joists that penetrate the wall construction, air can flow up through the cavity and along the path of the joist.
- Gaps between dry lining and ceilings
- Loft hatches
- Any gaps around ceiling lights, electrical sockets etc.
With careful detailing, using airtightness tapes, membranes and carefully considering the airtightness envelope these air leakage areas be can minimised. At one of our Passivhaus’ at Howe Park in Milton Keynes we managed to reduce the airflow leakage area down to the equivalent of a 50 pence piece. Below are some images of simple ways to reduce air leakage using airtightness tapes and membranes.