Retrofitting to PassivHaus standard
The secret in obtaining the best possible air test rating is paying attention to detail as early as possible in the project. That is the key to retrofitting to PassivHaus standards.
By the time one comes to air testing, a good way through the project, it is already too late and the ability to rectify defects becomes much more difficult and expensive in construction time and cost.
The best advice I can give is to employ an Environmental Buildings Consultant as early as possible and take on board what they advise.
It really is all about sealing the house around membranes which stop the passage of air. Traditionally built houses rely on air change through leakage around doors and windows, or trickle vents etc. PassivHaus, air-tight houses require alternative ventilation – usually in the form of MVHR.
One would think a fully built solid wall or cavity construction would be a barrier to air flow. Think again! Brick joints let air through because not all bed or perp joints have a perfect fill of mortar. Door and window frames leak too – all quite shockingly apparent when a smoke test is conducted and smoke comes out through the middle of a wall!
Plastering will go a long way to seal the house, but this is the final layer. Properly installed membranes and the stopping up of penetrations are vital. Every crack or abutment of different materials provides an opportunity for area leakage. Socket and switch boxes not made airtight will afford an opportunity for air movement.
One has to approach this as one would a military campaign – no stone unturned or issue not thought through.
The last thing is that the refurbishment is only as good as the quality of the construction trades being employed. From inception, each and every trade needs to fully understand the extent to which they have to pull together to meet the target. Continual education and meticulous attention to detail is key to meet the PassivHaus standard – maximum house volume air changes of no more than 0.6 per hour at 50Pa.
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