dry-lining / air tightness, minimal membrane punctures...

timmer3

hi folks. i'm dry-lining a house and take seriously the health concerns of phenolic solutions with the potential to trap moisture in the walls and grow mould etc. so i'm going for breathable and vapour permeable, i.e. a diffusion-open moisture membrane, with an air-tightness membrane also.

i got some great advice from an architect who suggested the following construction:
- air-tight membrane (tyvek) attached to concrete wall
- then fix the joists to the wall
- 100mm rockwool between joists
- vapour membrane (intello plus) on top
- breathable plasterboard (with breathable paint etc)

the logic behind putting the air-tight membrane in the warm side of the insulation is to reduce puncture points caused by the wall joist fixtures. but I’m thinking to myself, it’s going to be riddled with nails from the plasterboard anyway, I know these punctures will be small and the pressure from the board will reduce air-tightness loss... but there’s a risk there anyway to have the air membrane so close to the plaster. I can be very careful when fixing shelves and wardrobes etc but I think it would be easy to lose efficiency over years if someone forgets and pokes a nail in from time to time. Even if I sell the house in 10 years time I’d still like to leave behind a very reliable system.

could anyone comment on moving both membranes (not sure if they can be combined into one product) directly on to the concrete wall, and then attach the wall joists directly to the floor and ceiling joists, without any wall fixtures required. Where the membrane wraps into the floor/ceiling it could be taped around the vertical wall joists. this seems a lot safer in terms of the long term risk of puncturing the air membrane. i accept there is a load-bearing issue of resting the weight of the wall on the floor but i can't see it being a massive problem, a few joists and plasterboard.
services and cabling won't cause punctures either way, they will slot in behind the plasterboard regardless.

sydthebeat

tim,

how about copying this thread into the construction and planning forum as well...
it would be interesting to see different opinions between the two fora...

timmer3

good idea. thanks