Airtightning roof - Membrane tips and tricks?

[boxrick]

Hello folks

 

I'm about to fully membrane my ceiling before my cellulose insulation goes in.

 

Simply put I've watched a few videos about membraning. My joiners were going to do it, but I reckon myself and my girlfriend can do a better job.

 

With that in mind, can anyone share any resources or tips for me to get this right?

 

[MikeSharp01]

Two things we, my other half and I, learned from doing it really. First thing is to get the membrane which must be the reinforced type with the embedded net, as tight as you can so you limit the sagging you get when you pump in the cellulose. Secondly use the widest sheet of membrane you can get. We used the 4m wide stuff from intellio. Many fewer tape joints.

 

Our fixing was to clamp the membrane between the rafter and a counter batten running along the rafter with screws going through pre- drilled holes in the counter batten. Screwing ensures you can get it really tightly clamped and the holes make sure you get no jacking so you get an air tight seal around the screw hole, which if you think about it is actually filled by the screw anyway.

 

Once the cellulose was in and we had done the seals round roof lights and windows we got a 0.2 score on the passive house air test so something must be about right. 

[JohnMo]

We did double sided tape and stables (makes initial fixing easy), then taped all joints and taped over all staples. We then battened for a service void, with 50mm battens nailed in place through the membrane and double sided tape.

 

Only things going through membrane are MVHR, all wiring was attached to battens

[Oz07]

I managed on my own but was using 1 or 1.5 m wide, with 2 people it should be easier. I stapled mine up at start, ran it out 12m then stapled and cut off. Probably stapled it a few times on occasional ceiling chords as I ran it out. Taped over staples as above. I did 2 lots of counter battens and piloted and screwed the ones which punctured the membrane. Used some good 6x150mm screws at first but then I was using 70mm deep battens x2 to get 140mm total void. Only tip I can think of is with any decent sized penetrations (ie mvhr exhaust and intake) I traced round then cut a smaller hole than the pipe by about 10mm. Then when pushing the pipe thru this stretched the membrane and already gave a pretty good seal. Id probably then try to get some proper pre formed tape for holes. I just used loads of cuts of the airtightness tape going lengthways till the circumference of the pipe was done.