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Interesting, it looks (from some bodgey calcs) that PIR is still going to be better than a good insulating plaster. The room is on a top floor at the back of a victorian terrace. The rear wall had been rebuilt some time in the 60s so they concreted rendered the inside and then skimmed it. The difference in wall temps between that wall and the front wall which is still lime plaster is staggering.
terlg-
Thread dredge reply but i’m finally doing the insulation and just over half way through so a few observations and info for anyone else thinking of DIY internal insulation with phenolic foam backed plasterboard.
Unless your wall has less than 5mm tolerance for flatness it will likely need to be battened, my walls are mostly level for flatness and the foam can deal with any discrepancies apart form the odd place where we have had to think about fixing placement so as to not bend the board too much.
If you want to lower your EPC then take photos and keep receipts as you will not get a rating without documentary evidence of the installation
Don’t underestimate the time it takes to scribe a board edge and do any cut-outs for cabling and switches, we are cutting a rebate at the bottom of the boards for central heating/electricity and foil taping which is tedious despite working out an efficient way of cutting it back.
Don’t bother with thin boards, 50-60mm (62-72 total board depth) is the sweet spot and will get you close to new build regs for a solid out uninsulated cavity wall (not the recent new lower rating). beyond this depth your insulation gains aren’t increasing much and not worth the expense or loss of space, this will also make it compliant with building regs.The first room done is N/E facing and 2 exterior walls, we haven’t moved in yet but this room was always colder than the other 2 south facing rooms but with no heating on in the flat it’s noticeable the room is not colder than the others .
This stuff is expensive 15 boards cost us about £1850 as i forgot to order in advance and it’s hard to get stock especially if you need to order more or less than one pack of boards so paid a premium to get them at short notice.
Cold bridging needs to be looked at and I wouldn’t be comfortable doing an older property that had damp/moisture issues without dealing with those beforehand and getting professional advice on what insulation to use, I have concrete columns in the corners that will be left uninsulated as they are around 14in thick and a lower U value than a brick cavity wall but higher than an insulated one I have the boards to do them but that’s only if i get condensation on them which is unlikely but theoretically possible.
Not had a winter in this property yet but i expect it to make a difference as well as in the summer as the south facing rooms bake in the sun for most of the day.
Mr_Smyth
Well you can go thicker with the PB but you have to be aware of interstitial condensation and fix to walls accordingly. (Dot/dab or battens)
I’ll be fitting 62mm kooltherm K118 dot/dab to a 50’s flat in the new year.
I’m not going to be battling damp though as external brickwork is in good condition and no rising damp as it’s on 6th floor.
Solid walls would mean a bit more thought regarding any existing damp issues.
I’m hoping it makes a difference to warmth/heating and also in the summer.