One of the air tightness tests I carried out last week was an on-completion air permeability test on a home in the Eden Valley / Penrith area built to Passivhaus standards. The only heating installed in the 70 sq m footprint building is electric underfloor heating in the bathroom and a multi-fuel stove in the living area. The measured air permeability was about 1.7m3/hm2@50Pa, but on investigation most of this amount related to the treatment of where the flue pipe goes through the roof. Building Regs clearly must be adhered to, but there are grommets out there that are rated to withstand the exterior temperatures experienced with some twin wall flues – enabling airtightness and compliance with Part J.
As an experiment, we temporarily taped over this area and the air permeability dropped to under 0.5 m3/hm2@50Pa – giving an air change rate well within Passivhaus requirements if a grommet is fitted.
Luckily the client has yet to finish the ceiling and so the remedial work is straight forward.