January 30, 20197 yr Hello all, I'm looking at ways to reduce the cost of my kit house, one big saving is to get the kit uninsulated and installing the insulation myself. I wanted to hear some opinions on using the 140mm Knauf Frametherm Insulation inside the 140mm Kit Frame, then using rigid Celotex type board on the inside face of the kit with a foil barrier. I've seen some kit manufacturers offer this option but my Architect is advising that its not good to mix the insulation types in the wall (wool and celotex). Is this correct? The U Values look to be the same and I imagine its a lot easier using the frametherm than trying to cut 120mm celotex boards neatly to fit in the verticle studs. The kit I'm looking at has 120mm Celotex in the kit frame and 50mm celotex on the inside face. If I get the kit without the insulation it's £9800 cheaper. Picture below shows what I'm looking at doing.
January 30, 20197 yr we went with a similar mix- 140 of Frametherm 35, VC Foil Ultra, 40mm PIR, service void. As all the insulation arrived today, I've just sat with the calculator and totted up a guestimate of it's value and it's somewhere around the 6k mark.
January 31, 20197 yr I used Frametherm, 2 layers of 100mm in a 195mm frame. Of all the wool type roll insulation it is the least nasty one to handle. The best price I could get for it was from SIG buying the whole lot in bulk.
January 31, 20197 yr 9 hours ago, DonGillies said: but my Architect is advising that its not good to mix the insulation types in the wall (wool and celotex). Your architect is incorrect. It’s okay to mix insulation types and the way your diagram shows it is the correct method. British Standard 5250 recommends that: Page 92 If different types of insulation are used in successive layers, the layer with the greater vapour resistance should always be placed closer to the heated interior Edited January 31, 20197 yr by Ian
January 31, 20197 yr Your buildup is pretty much exactly what I'll have for the gable walls, but mine will be a bit thicker. Biggest difference is I'm thinking I'll put the vapour barrier behind the PIR to protect it. Outside in: TF200 9mm OSB3 235mm rockwool insulation between 235mm JJI I-beam studs. Polythene vapour barrier. 90mm PIR. Battened service cavity. I don't see any problem with mixing insulation types so long as, as we have, the more vapour-open stuff is on the outside.
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