Warmdeck Roof Insulation - Layering

21 Mar 2016
Reaction score
United Kingdom
I remeber reading somewhere that, although polyisocyanurate PIR insulation look good on specs but performs poorly in low temperatures.

If laying 150mm warmdeck roof, is it better to layer it as follows:

(1) Layer1 - 50mm PIR (warm side)
(2) Layer2 - 50mm XPS/EPS Polystyrene (to prevent cold-bridging with 3rd layer cold side)
(3) Layer3 - 50mm PIR (cold side) but foil-faced for accepting adhesive roof covering.

I've stuffed 100mm PIR in the floor slab thinking it was best insulation but looking back I think it was a mistake. EPS/XPS was more ideal for floor slabs, and cheaper. Only positive in that is that at least the floor isnt exposed to very low Winter temperatures.

Any expert comments please?

Thanks for looking.

Sponsored Links
Have you been reading a sales pitch from a polystyrene supplier? Ignore any slanted or prejudicial nonsense documents supporting one product over another.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links