Building air tightnesscan be defined as the resistance to inward or outward air leakage through unintentional leakage areas within the building envelope. This air leakage is driven by differential pressures across the building envelope due to the combined effects of stack, external wind and mechanical ventilation systems.
Why its important to have Airtightness:
Around 15% of the total heat produced is lost through drafts. This represents an enormous amount of heat but for a well-insulatedhome these losses represent a much larger portion of the heat lost. Airtightness is a critical aspect to consider when building low energy buildings as the effectiveness of insulation is massively reduced by poor airtightness.
The other consideration is that as buildings become better insulated any air leakage has more of a chance of condensing within the walls during the winter and causing issues with moisture. This can affect both timber framed buildings and masonry buildings alike as it not only reducesthe effectiveness of the insulation, but it can also cause timber to decay.
How to achieve Airtightness
There are different options available to create an airtight layer on the building envelope. External block walls are only airtight by having an internal plaster applied straight to the block work. Please keep that in mind in case you decide to use an internal insulation, such as insulated plaster board.
In the case of timber frame structures, such as pitched roof areas or complete timber frame houses it is possible to apply an airtight membrane or OSB.Overlaps, joints and penetrations need to be sealed by using special airtight tapes or airtight materials like patches, sleeves or grommets.
The joints around the external windows and doors need to be sealed as well. You can choose between various window sealing tapes for this purpose.
Advantages to having an Airtight Building
When you have anairtight building, you have an extremely energy-efficient building because the mixing of indoor and outdoor air is extremely limited, which reduces the energy bills associated with heating and cooling