Celotex alternatives

[olivermarshall]

Hi all

I'm finally lining my loft. I was looking at 25mm or 50mm celotex to go underneath the plaster board but I'm also keen to not have to sell a kidney to do so.

Before I commit, can anyone recommend a more affordable alternative for insulation to go between the roof tiles and the plaster board?

Olly

 

[freddiemercurystwin]

All PIR insulation types perform pretty similarly, there are plenty.

 

[Notch7]

Kingspan, ecotherm, quinntherm.

 

[JP_]

my builders used Ballytherm. I don't know where they got it from but it is on http://www.insulation4less.co.uk/ballytherm-roof/

 

[foxhole]

Do a proper job , 100mm between rafters then insulated plasterboard over the top.

 

[JP_]

Insulated plasterboard is expensive. Why not 25mm over the top and then board? I had this in my loft. With a nice large window it was warm enough in winter to not need a jumper.

 

[freddiemercurystwin]

Nothing wrong with separate ins and board.

 

[JP_]

I bought insulated plasterboard for my internal insulation last year. Cost about the same as separates, but for half the insulation, and half the quality. (20mm insulated board about same as 50mm Kingspan + board).
And, much harder to work with. I sent it back.

 

[oldbutnotdead]

If you've got the headroom, rockwool is much much cheaper than the Kingspan etc boards and performs much better acoustically (reduces sound of rain on roof quite a lot). Haven't got the exact figures to hand right now but from memory 70mm Kingspan came in at about £10/sq metre (this is a couple of years ago) with rockwool (150mm) coming in at £3/sq metre for the same thermal performance (and much easier to get a good airtight fit). Of course rockwool doesn't work well with dot and dab but in your situation (if you have the headroom) it'll be a lot cheaper to hang 150mm boards from the sides of your rafters (at about £1/metre), stick some laths across between rafters to maintain 50mm airgap under the felt/membrane then rockwool (150mm) then pb screwed to the boards. Surprisingly, the rockwool doesn't sag and droop as much as you'd expect it to (if your rafters are between 400 and 600 centres)

 

[JP_]

Maybe do a combo like I did in my floor - with rockwall between the rafters and then overboard with 25mm board?

 

[cdbe]

Get searching on ebay - there are bargains to be had! I recently got 100mm sheets for £20 each and some 50's for £12. I also got loads of this for £2/m (but it's in Bradford)

It's 100mm thick recovered from commercial insulated panels.

Otherwise Selco do 50mm for £27 if you have one nearby as the big suppliers charge a lot to deliver a small quantity.

The plasterboard bonded stuff is nice (well it is when you get 7 sheets of 50mm for £50!) but otherwise vastly overpriced and completely ridged - makes it murder to get up stairs as it doesn't bend at all. I've just underboard my bedroom ceiling with it:

 

[pilsbury]

PIR insulation is robbery. All the brands are similar cost. Only cheaper option is seconds on fleabay.