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Best way to insulate flat roof

The home for the various ways, products and methods to insulate lofts and roof spaces.

Best way to insulate flat roof

Postby Tim45 » Sat Jan 08, 2011 7:59 pm

We have a small ground fl0or kitchen extension and the roof needs re-felting as it is cracking a little and has seen better days. Its a shame it was never done as a pitched roof as am not a big fan of flat roofs.

As the roof is going to be off i wondered if it would be worth insulating the flat roof as the company we spoke with who will be doing the work didn't seem that knowledgable in this area, which is a little concerning and were not planning to do so.

Is there a standard way to insulate a flat roof?
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Re: Best way to insulate flat roof

Postby Angib » Sun Jan 09, 2011 1:12 am

Hmm, tricky. However this is the one and only opportunity to insulate the roof until the new roof coating wears out in another 10-20 years, so it's a great idea to do it now.

The downside is that insulating flat roofs requires a fair bit of knowledge and lots of jobbing builders don't have that knowledge. Of course companies specialising in this sort of work do have the knowledge, but they are usally much more expensive to employ.

Here is the rather technical Energy SavingTrust guidance on flat roofs - to be fair this is the advice to 'building professionals', not homeowners. That links to a refurbishment guide which has one page (p17) on flat roof insulation.

It would be worth getting a quote from a specialist company - maybe if only to convince yourself that you are better off paying higher energy bills than insulating!

On Edit: Of course I should have added that by far the cheapest way to insulate a flat roof is to add insulation below the ceiling - typically by adding a layer of insulation-backed plasterboard (or plasterboard-faced Kingspan, if you want to look at it that way) and then skimming over that and redecorating. The problem with that is that lots of flat roofs have been used on extensions that are already tight on headroom, so losing even the 60-80mm depth of the insulated plasterboard can be unacceptable. But if not, it's the easiest way to do it.
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Re: Best way to insulate flat roof

Postby Tim45 » Thu Jan 20, 2011 1:44 pm

Many thanks Angib, very helpful. We did think about putting insulation inside but the ceiling is not very high at minute and this would make things even worse. Plus we would need to sort electric out etc. I have spoken to a builder who has shown me a membrane which looks good. I am waiting for costs which am dreading :(
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Re: Best way to insulate flat roof

Postby Henry » Mon Jan 31, 2011 11:25 pm

Hi,

There are a couple of methods I've read about when doing my own research, not an expert myself I'm afraid nut perhaps worth speaking to a builder about them:

Inverted Roof:
This type of roof uses waterproof insulation on the top of the roof. Basically you lay the insulation on the top of your flat roof over the existing waterproof membrane then put something on top to hold it down. This could be turf or paving slabs for example, or even gravel. The potential problem is that water can sometimes work its way down to the membrane which can cause condensation.

Warm Roof:

This type of roof has a vapour control layer over the roof deck, then the insulation itself, then a membrane over the isulation and finally a suitable finish. This is (apparently) a better solution than the inverted roof provided you are replacing the roof membrane anyway, though you can leave it in place if you would have difficulty removing it.

In either case you will need to check that the roof structure can take the additional weight and as with replacement roof covering which is anything other than a like for like change you will need building regulations approval.

Best regards

Henry
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Re: Best way to insulate flat roof

Postby JohnWilliom » Thu Apr 07, 2011 9:34 am

The benefits of foam roof insulation are many and this article will list some of these positive properties of foam roof insulation. Foam roof insulation is a polyurethane foam product that is applied directly to the roof of a building.
Last edited by HEA on Thu Apr 07, 2011 9:51 am, edited 1 time in total.
Reason: link removed
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