Any Builders on Here?? ( Roofers)

Here we go:

Right, my flat roof started leaking. Had it all removed, boards were totally soaked.
New OSB(?) fitted with EPDM (1.5mm). It is now waterproof.
On the inside I haven't a ceiling as yet.
What I need to know is, what/how do I insulate between the roof joists?
The joists are 400mm (16") centres and are 150mm (6") deep.
Width of room is 2.3 mtrs x 3.34mtrs.

Can I use these poly blocks from B&Q:

www.diy.com/nav/build/insulation/constru...-Board-Pack-10647759

If you get my drift, 1 pack would do 1 'gap', there are 8 'gaps' to fill. = £80
As they are only 60mm deep, should I double them up? (£160)
This would make the insulation 120mm so leaving me a 30mm air gap below the underneath of the roof boards.
Also, would I need a damp barrier thingy? If so, I presume plastic sheet tacked to the underside of the joists before the new plasterboards go on?

Any help/advice would be much appreciated and ASAP, sorry!

All the above is just what I've read on the interwebby tonight.
This is how it looked last week. As I said, slight leak....





Thanks again for any help etc..

Keith

wow.my flat roof single story extension has a slight leak were it meets the house uv scared me now.

As you have described so far, you will be creating what they call in the trade a “cold roof”.

The setup you have described will work fine, apart from you needing to add ventilation You want to use some thick damp proof membrane (50 guage)



I'm not a builder, but i have a degree in Architecture & Property Development

Thanks Adam, a proper thanks.
I was lost as to what I needed, what should be done etc but you've explained it brilliantly for me.
I read that and understood it straight away and the diagram.
Much appreciated, again thank you.
(And I won't mention anything about your Jim being that other than black colour)
Keith.