Hello,
Sorry if this info is elsewhere in topics but I am mega confused and have read the other posts to no avail!
OK so long story short... building an extension and I am confused by the roof detail. The plans have been signed off by building control but a bit worried that even though that is the case when I actually come to build the roof the BCO will say oh that was wrong on the plan!
I think our plans specify a COLD roof/un-ventilated (which I think is the one with a breathable membrane?)
1) Wouldn't it be better to have breathable membrane on a warm/ventilated roof too?
So our plans specify 125mm rafters with 100mm celotex between and 50mm celotex under rafters, this leaves 25mm gap from top of insulation to the top or rafters. Then specifies breather membrane draped.....
2) Does this mean lay it right onto insulation between rafters? I got confused here as the celotex sit u-calcs seem to specify minimum 25mm cavity and I assumed (as I believe is the case on the Warm Roof that the cavity is classed as between the breather membrane and the back of insulation)
I am needing to order my timber so if this is wrong and I actually need 150mm rafters i.e. 10mm insulation cavity of 25mm to draped membrane then 25 mm to top of rafters where there will be the cross batten then it would be wise to get it right now! So...
is 2) wrong and I should do 3)?
Finally I also I believe if i have 150mm rafters I could do 100mm insulation then 50mm air gap then membrane (non breathable tight over rafters, then cross battens and tiles?
4) I believe then I have to ventilate that 50mm cavity below the membrane? so does this mean more than just ventialtion between tiles and membranes?
5) whcih would people reccomend in their experiences?
Sorry if all my thinking is ar$e about face as you can see I am a tad confused!
Many thanks in advance
Sorry if this info is elsewhere in topics but I am mega confused and have read the other posts to no avail!
OK so long story short... building an extension and I am confused by the roof detail. The plans have been signed off by building control but a bit worried that even though that is the case when I actually come to build the roof the BCO will say oh that was wrong on the plan!
I think our plans specify a COLD roof/un-ventilated (which I think is the one with a breathable membrane?)
1) Wouldn't it be better to have breathable membrane on a warm/ventilated roof too?
So our plans specify 125mm rafters with 100mm celotex between and 50mm celotex under rafters, this leaves 25mm gap from top of insulation to the top or rafters. Then specifies breather membrane draped.....
2) Does this mean lay it right onto insulation between rafters? I got confused here as the celotex sit u-calcs seem to specify minimum 25mm cavity and I assumed (as I believe is the case on the Warm Roof that the cavity is classed as between the breather membrane and the back of insulation)
I am needing to order my timber so if this is wrong and I actually need 150mm rafters i.e. 10mm insulation cavity of 25mm to draped membrane then 25 mm to top of rafters where there will be the cross batten then it would be wise to get it right now! So...
is 2) wrong and I should do 3)?
Finally I also I believe if i have 150mm rafters I could do 100mm insulation then 50mm air gap then membrane (non breathable tight over rafters, then cross battens and tiles?
4) I believe then I have to ventilate that 50mm cavity below the membrane? so does this mean more than just ventialtion between tiles and membranes?
5) whcih would people reccomend in their experiences?
Sorry if all my thinking is ar$e about face as you can see I am a tad confused!
Many thanks in advance
