Expanding foam in insulation?

[flobadob]

I'm putting kingspan 100mm foam board insulation into my kitchens flat roof. I've already taken down the plasterboard and put in most of the insulation. My mate reckons I should put expanding foam between the gaps of the boards. Is this overly necessary, and will it make a big difference to the final outcome? I wouldn't bother unless it was going to make a big difference.

[Mick-Talbot]

Depends how bad your cuts are.

[Mick-Talbot]

if you have plenty of room and the budget , Go over the lot (joists and the 100 mm kingspan) with 20 or 30 mm kingspan.

[flobadob]

The gaps aren't too bad. I was told there needs to be some gaps so that the air can circulate so as to avoid damp and rot developing.

[The Builder]

Current thinking is to avoid draughts Flobbers. The better the insulation the more likely cold air is to seek out any gaps ............. thus reducing the value of the insulation.
Mick's idea is a good one. If you do ......... tape the joints (draughts again), and use longer plasterboard screws .
If not ................ then staple a thin polythene vapour check all over the joists before boarding.
Foam can be messy ............. but worth it.

[AlBags]

Use foil tape on joints.
Boards should fit tightly
Use foil faced board if kitchen or bathroom.

[flobadob]

The kingspan is foiled and I've stuffed some fibreglass from a roll I got in some of the gaps. There aren't too many gaps as I cut the board pretty tightly most of the time. I'm thinking maybe it will do unless someone reckons I should definitely do something else.

[The Builder]

Fair enough Flobbers .................. but I'd still use a vapour check in the kitchen :o)))

[flobadob]

What is a vapour check anyway builder?

[The Builder]

See my answer above Flob ...............
It's thin polythene simply to prevent the (large) amount of water vapour created in a kitchen from getting into the roof, condensing, and setting up nice warm conditions for rot to develop. :o)))

[flobadob]

Cheers, might look about doing that monday.

[AlBags]

As I have already mentioned ... you should use Foil-backed board.
To help you ..
http://www.diynot.com...f9b18743e8147310e15c5