boxrick Posted Wednesday at 08:45 Posted Wednesday at 08:45 Hello folks! In summary I am about to install a posi-joist roof sat on some steel ridge beams. Probably filled with cellulose or rockwool, running MVHR through the posi-joists and having the ceiling vaulted. I am currently trying to decide what type of breathable roof membrane to use on top of the OSB3 Sarking Boards. Does anyone have any recommendations of any products which excel at this?
JohnMo Posted Wednesday at 10:10 Posted Wednesday at 10:10 Almost any breathable membrane will be fine, use what's on your drawings. We used Proctor. Would you be better to use sarking boards instead of osb, once installed these will shrink a little and give lots of small slots to let moisture ladden air out.
boxrick Posted Thursday at 11:16 Author Posted Thursday at 11:16 On 16/07/2025 at 11:10, JohnMo said: Almost any breathable membrane will be fine, use what's on your drawings. We used Proctor. Would you be better to use sarking boards instead of osb, once installed these will shrink a little and give lots of small slots to let moisture ladden air out. I need this slightly structural to prevent the twisting my valley beams. Woodfibre sarking boards don't seem to offer any of that. Looking at other softwood 'sarking' boards they seem to be basically just fence panels and about 2x the cost. ( I need around 140-160msquare coverage ).
JohnMo Posted Thursday at 11:56 Posted Thursday at 11:56 34 minutes ago, boxrick said: Woodfibre sarking boards don't seem to offer any of that. Sorry I was thinking more Scotland and the mandatory use of sarking boards for increased wind loads. Bit different from fencing - but not much. Mine in the process of being installed. Gaps are used to traverse the roof and are back filled when finished. 1
boxrick Posted Thursday at 21:06 Author Posted Thursday at 21:06 9 hours ago, JohnMo said: Sorry I was thinking more Scotland and the mandatory use of sarking boards for increased wind loads. Bit different from fencing - but not much. Mine in the process of being installed. Gaps are used to traverse the roof and are back filled when finished. Which ones did you go with?
JohnMo Posted Thursday at 21:19 Posted Thursday at 21:19 11 minutes ago, boxrick said: Which ones did you go with? Correct sarking boards, from memory 22mm x 150mm
SBMS Posted Thursday at 22:18 Posted Thursday at 22:18 We are using 22mm steico universal boards with pro clima solitex plus.
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