The buildings that exist today will account for over 70% of the total building stock by the year 2050, so how we make them energy efficient is very important. The United Kingdom’s first Retrofit Passivhaus project was completed in early 2011. It is recognized that, particularly orientation (which affects solar gain), is unchangeable in existing homes, but it is still possible to retrofit to Passivhaus standards.
- Removing all wall linings, plumbing & electrics;
- New rear external insulation & triple glazed windows fitted;
- New continuous airtight layer of Oriented Strand Board (O.S.B)/Plaster.
The project, architect Robert Prewett, suggests that attempting to reach Passivhaus standards without removing all the internal linings would make the task considerably more difficult and potentially risk the existing fabric, because e.g. damp may not be obvious. Air leaks resulted between new and old plaster and the MVHR and ducts were difficult to fit in. This suggests that the Passivhaus approach should only be considered where no original features require being retained.
Traditional buildings behave in a different way from modern buildings in relation to moisture, air movement and thermal performance, and are more likely to be built from porous “breathable” materials which allow natural air movement and deal with moisture build up through evaporation. Many United Kingdom homes have successfully dealt with the weather for 100 years. Applying modern design methods is not always appropriate and can lead to moisture build up and fabric deterioration. Only research on the long term effects of Retrofit Passivhaus will prove how appropriate a method it is for existing buildings.
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