I am expecting to move into a bungalow within the next eight weeks.
I plan to board part of the loft to provide storage but the remainder mostly has glass wool between the joists but not raising higher. government guidelines recommend not less than 270mm.
I was thinking of adding 200mm. Am I overdoing it?
Also, any suggestions as to the best supplier? I am in Harrow.
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You cannot apply until you own the property. :(
There's a graph of the U value here:
Assuming you're starting off with 100mm, the returns start to diminish after about 125mm. But if you're going from U=0.3 at 100mm to U=0.1 at 300mm, that's cutting the heat loss by two thirds (if I read the graph right).
Your call as to how much you want to spend. IMHO the labour/hassle factor means I'd spend a bit more on materials to get thicker, even if the difference is marginal. That assumes you have enough headroom to fit it.
Wickes and B&Q if you're buying small quantities. I found Wickes click and collect was mayhem when I went before Christmas - not going there again any time soon.
B&Q have: Knauf Eko Roll Loft insulation roll, (L)5.68m (W)1.14m (T)170mm £24 Buy any 3 Eko Roll loft insulation rolls for £17 each. (£2.62/m2)
Knauf Eko Roll Loft insulation roll, (L)4.83m (W)1.14m (T)200mm £25 Buy any 3 Eko Roll loft insulation rolls for £17 each. (£3.09/m2)
Wickes 170mm is £2.55/m2 Wickes 200mm is £2.94/m2
Local BM (AR Aspinall) quoted: Knauf Loft Roll 170mm 8.01m2 £23+VAT (£3.45/m2)
Gibbs and Dandy (local chain BM): isg05771-superglass-multi-roll-44-2x580-3x386-1x1160x485m-200mm (that's 5.62m2 of 200mm thickness) £16.55+VAT (£3.53/m2)
There are also online suppliers - that might make sense for larger quantities.
But of course the local BMs have free rapid delivery, while B&Q charge and Wickes you have to book several days in advance. Ordered from G&D, they said they were very quiet, van came 9am next day.
Theo
DIY loft insulation is cheap, and better done if you do it yourself.
Use extenders to raise you boarded area with these -
Arrange for these horizontal 50x50 bars to be about 600 mm apart and this is what supports your boarding. OSB is lighter than ply if you are worried about deflection of the ceiling.
Thank you very much for that post!
I used rigid board insulation (90mm) on top of the existing joists which already had insulation between them. With care can then be walked on or used for light storage of overlay again with chipboard or hardboard.
Yup. I did this when I had the attic rooms ceiling down. I did the calculations at the time and worked out 50mm was the most efficient in terms of cost, insulation and ventilation. And for a storage space/one you're going to be walking in, so much easier than stilts/boards etc.
It's not impossible to have a mixed plan - use PIR boards for the parts don't want to raise, and fibreglass/mineral wool for the parts you don't care about.
Most PIR has a resistance double that of mineral wool, so 50mm PIR is equivalent to 100mm mineral wool. If the OP wants to go for 300mm of wool, that means 150mm PIR. I would probably compromise a bit to make the heights work - maybe 90mm PIR between 100mm joists?
Theo
(I'm currently replacing patchy wool between 120mm deep rafters with 50mm celotex, for coverage, breathability and improved heat reflection. Further down the road I'll look at 100mm celotex under the boards between 120mm joists)
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