Airtight envelope

[iansr]

I’ve read that your airtightness strategy should start by deciding where the  boundaries of your airtight envelope will be.  So the easy part of that is to decide on the floor of the ground floor and the internal faces of the external walls (which will be wet plastered).   The bit I haven’t got my head around is where to have  the boundary at the top of the house?  Is there an optimal answer?  Should it be the inner face of the top floor ceiling or should it be in the roof space and if so precisely where and how?

 

Any wisdom on the subject will be gratefully received!

Edited November 17, 2021 by iansr

[Iceverge]

We did ours below the roof trusses at ceiling level. 

Then a service cavity and then plasterboard. 

 

We left a gap between the roof trusses and the top of the internal walls so we could run the membrane uninterrupted from external wall to external wall.