Loft insulation – how deep

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  • Loft insulation – how deep
  • We have loft insulation about 6-8 inches think of the itchy stuff but in a pink bag at the moment. Just aquired a load of B&Q vouchers and noticed they are doing massive discounts on loft insulation. Is there any benefit in putting another layer down or is the money better wasted elsehwere?

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    Based on my latest calcs for my new house:

    K Depth mm R
    Rsi 0.1
    Rso 0.04
    Ra 0.18
    R1 Roof tiles 0.85 20 0.02
    R2 Felt 0.50 3 0.01
    R3 Insulation 0.044 300 6.82
    R4 Pasterboard 0.16 15 0.09
    Sum 7.26
    U Value 0.14

    roof has a target U value of 0.16
    300mm of rockwool just beats the target.

    EDIT: Sorry, tables dont work in phorum.
    Anyway, 7" gives you a U value of only 0.22


    I've 8" (snigger) with some loftboards on top, I think any more than that and you're not going to see a lot of benefit

    B&Q have their insulation this cheap every year. They have 15% off if you spend over £50 tomorrow onwards (but they do that quite often too).


    suggests going 5cm-25 isn't a huge benefit, so I recon 20-30cm is even less?

    I'd waste your money on some spades, and build a nice trail. Or, some loft boards, board it, stick the wife up there and turn the dining room into a bike workshop

    Most of it is already floorboarded. Double garage with beer fridge and sauna for work on the bike. I live a gifted life.


    keep an eye out on Money saving expert (or Npower) as Npower do a thing of £1 per roll of rockwool insulation.

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