Airtight is right! Balancing airtightness and ventilation

Have you ever visited the home of an older relative in the winter who has a cold home because their windows are always open to help with ventilation? There exists a long-established practice that this is the only way to bring fresh air into a home.

There might be good reason for that. Homes built as late as the 1950s might not have had any insulation in the outer walls. And they were heated by radiators placed at the windows. This creates uncomfortable hot spots in a home including condensation near any glazing. So cracking open a window tried to address both issues.

Today it is fairly common knowledge that insulation is an essential part of creating a good home. Less known is that reducing the draughts that blow through walls is possibly more important. This feature is known as airtightness. Insulation and airtightness are the equivalent of a wool jumper and a windbreaker. With both, you are kept warm from cold temperatures as well as cold winds.

How to achieve better airtightness

Creating an airtight home requires special knowledge of materials as well as how pieces of the building are put together. It is not only important to specify the correct kind of window, but to install that window in a way that reduces how much wind comes through the joints where the window meets the wall.

And if you manage to do this, you will have a building which actually keeps all the heated air within the rooms. As a note, building regulations allow four times the air of a room to be replaced every hour in order to keep occupants oxygenated appropriately; so there is an acceptance that this means whisking away all the heated air out of a room every 15 minutes. Talk about energy use!

Airtightness is measured in air changes per hour at an imposed pressure differential of 50 Pascals. Building Regulations demand a maximum air leakage of 10 m³/hr/m², while the RIBA Climate Challenge asks for 1 m³/hr/m² and the Passivhaus target is 0.6 m³/hr/m² @50 Pa.

Whilst ensuring the right airflow and ventilation

For homes that are seeing substantial renovation to the outside, it is very easy to upgrade the walls and roof to increase airtightness. And in these cases, we would promote the use of an MVHR which stands for mechanical ventilation and heat recovery. The job of this kit is to bring in fresh air and put it in contact with the heated air that is being extracted from the home. In this manner, rooms are kept well ventilated but far less energy is lost.

You can get more understanding about an MVHR from this great video on the Green Building Store’s website.

To understand more about the alternative technologies that can reduce your heating bill and carbon footprint at the same time, read our blog on air source heat pumps.