New Insulation in Pitched Roof to Fix 2 Top Rooms in Eaves


Postby sigcima » Fri Dec 11, 2015 8:21 pm

Hi All

First visit here and I'm hoping you can help. I've done an amount of research but remain confused as to what to do next.

I have 2 bedrooms "up in the eaves" which have inadequate insulation between the rafters and on the side walls. The rooms are freezing in winter and boiling in summer (a give away as to the poor insulation). There is currently ill fitting polystyrene which probably dates from the 1980's shoved between the rafters with masses of air gaps between the sides.I want to cost effectively remedy this situation as best as possible with little disruption to the inside pasterboarding. The rooms also have side blockwork walls about 2.5 to 3 ft high which are not insulated at all out to the "cold roof" which I also want to insulate, thus bringing the wall and pitched roof insulation together to remedy the situation to reasonable standards given the situation (not going to be passive house or anything!). I can access the cold roof space at the sides of the room via access hatches in the walls, and from there I can slide out the existing polystyrene and there should be enough space to slide in a compete new slab of PIR board.

What is the best solution for the combined pitched roof and side wall? For the pitched space between the rafters I am considering either Xtratherm Pitched Rood XT/PR boards (which I would have to cut), or Xtratherm Rafterloc (which don't seem that readily available), or Celotex GA4080 board, or Rockwool Flexi. All of these will have to be slid into the rafter space from the access space in the side loft. Which is the best solution of those for both thermal performance and ease of installation? Then I need to attend to the side wall, should I use similar PIR board and stuff any joining gaps with some sort of gap filler. As this will be more of an expanse I was thinking definitely of some sort of interlocking/tongue and groove product.

What I cannot do is fit any of this from inside as the plasterboard is already in place and I don't want to take this off and re-fit this and redecorate, unless it cannot be avoided.

Thanks
sigcima
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Postby tileclipproman » Sat Dec 12, 2015 12:32 pm

New regs are 6inches of kingspan or similar,1ft of glas fiber insulation.I presume your rafters are 4inch so that leaves only one choice without reboarding.YBS super quilt multilayer insulation about £130 per 1.5mx10m per roll its the stuff that looks like a space blanket.The thermal value is as good as the king span so I am told.
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Postby sigcima » Sun Dec 13, 2015 12:38 am

tileclipproman wrote:YBS super quilt multilayer insulation .


I'm not sure how I would install that with it being flexible. If i tried to push that into the voids between the rafters would it not be like 'pushing on a string'? As this is a DIY project I wasn't going to pay to much attention to 'regs', so thought 80mm of Xtratherm would do it between the rafters. This would however only leave 10mm of gap up to the roof felt/membrane. The product sheet recommend 50mm gap to prevent condensation. Anyone got any views on that. I'm not sure I wanted to go as thin as 40mm on the insulation as I'm not sure the result will be that great. What's the smallest gap i would get away with up to the felt?
sigcima
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