The U value for the traditional Irish timber frame wall construction is 0.21 W/m2K; this does not satisfy the passivhaus standard.
When we examine the timber frame system flaws in its design become evident. One area which needs to be addressed is the level of insulation. As a result of the level of insulation in the walls there is high heat loss which is not feasible when trying to satisfy the passivhaus standard.
Airtightness is another crucial factor when trying to prevent heat loss through the structure; air leakage must be eliminated.
Timber frame construction is quite challenging to make airtight; when installing the membranes high quality workmanship and attention to detail is crucial; every joint must be carefully taped or sealed (with mastic) to ensure it is airtight. The Irish standard (Part L 2011) for airtightness is 7 m3/h.m2 at 50 Pa (seven cubic metres of air change per hour for every square metre of floor area when the difference in air pressure between inside and outside is fifty Pascals), this is quite a low level of airtightness when compared to the passivhaus standard of 0.6 m3/h.m2. This portrays the difference in the level of detailing and quality workmanship needed to achieve the passivhaus standard.
The sketch below is a Passivhaus detail; compliments of Integrated Energy, Crean Salley Architects and Shoalwater Timber Frame. In this detail thermal bridges and air leakage which are evident in the traditional timber frame construction are eliminated; this provides the structure with the opportunity to reach the passivhaus standard of between 0.10 - 0.15 W/m2K.
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