Air infiltration through the fabric of the building (cracks, gaps in door/window frames, etc.) participate to the indoor air renewal by letting fresh air in or exhaust air out depending on how air pressure is applied outside the fabric (by the wind) and inside (by fans, air density, etc.). However, air infiltration is totally uncontrolled, can lead to excessive heat losses and condensation within the fabric of the building, as well as creating discomfort due to draughts.

With constant improvements in energy standards in homes, airtightness has become a key requirement to achieve a good level of energy efficiency. This is achieved by using membranes, tapes, gaskets and sealants to create a layer impermeable to air wrapping the whole house. Openings such as windows and doors must be also be installed in an airtight manner at the junction with the building fabric (wall, roof) and close tightly. The airtightness of existing homes can also be improved by applying some of the above measures where possible. Part L of the Building Regulations sets out the minimum level of airtightness in new Irish houses (7 m3/h,m2 when blower door tested at 50 Pa).

However, in our rush to make homes more airtight, we should also be very conscious that providing purposeful ventilation becomes essential to maintain good IAQ.

Links:

• IEA, Ventilation and Air Infiltration Centre http://www.aivc.org/index.html
• Passive House Institute, http://www.passivhaustagung.de/Passive_House_E/airtightness_06.html

Downloads:

• Study by the NHBC Foundation:  Indoor air quality in highly energy efficient homes – a review
• Report by the NHBC Foundation on airtightness and ageing
• A practical guide for building an airtight house by the NHBC Foundation