Flat Roof Insulation

jkavanag · 18-05-2019 6:48pm #1

Hi

I am doing an extension with a flat roof and I was hoping to get some advice re the insulation. We are planning on using torch on felt and having a cold roof as we want to be able to deck it for a roof garden in the future.

The insulation guys are telling us to use a 50ml Kingspan insulated slab together with 200-300 ml of fibreglass between the joists and the steel. It will be vented out for air circulation to protect the ply. The builder however is telling me that he thinks the insulated slab will do the job on its own and keep the house warm enough.

Has anyone any experience of this or any advice?

Many thanks
JKav

sydthebeat · 18-05-2019 7:18pm

jkavanag wrote: »

Hi

I am doing an extension with a flat roof and I was hoping to get some advice re the insulation. We are planning on using torch on felt and having a cold roof as we want to be able to deck it for a roof garden in the future.

The insulation guys are telling us to use a 50ml Kingspan insulated slab together with 200-300 ml of fibreglass between the joists and the steel. It will be vented out for air circulation to protect the ply. The builder however is telling me that he thinks the insulated slab will do the job on its own and keep the house warm enough.

Has anyone any experience of this or any advice?

Many thanks
JKav

No it won't.

You can't substitute 200-300 mm of quilt and expect the same results.

However, it sounds to me like you have no professional advise on your build (builders are not professionals)

Get someone involved who isn't working for their own profit.

jkavanag · 19-05-2019 1:43pm

Thanks Sydthebeat.

I have paid for plenty of prof advice as it happens. The architect though is MIA because he was paid 6 months ago and isnt overseeing and the engineer is on his holibops for two weeks. The builder is just trying to save me money in fairness to him but I would veer to the safer side and insulate as best as possible. It seems to me that something like this should be fairly standard though.

Bullocks · 19-05-2019 1:57pm

jkavanag wrote: »

Hi

I am doing an extension with a flat roof and I was hoping to get some advice re the insulation. We are planning on using torch on felt and having a cold roof as we want to be able to deck it for a roof garden in the future.

The insulation guys are telling us to use a 50ml Kingspan insulated slab together with 200-300 ml of fibreglass between the joists and the steel. It will be vented out for air circulation to protect the ply. The builder however is telling me that he thinks the insulated slab will do the job on its own and keep the house warm enough.

Has anyone any experience of this or any advice?

Many thanks
JKav

I would be using the fiberglass.
Can a warm roof construction not be used for a roof garden?

Bonzo Delaney · 19-05-2019 3:38pm

Bullocks wrote: »

I would be using the fiberglass.
Can a warm roof construction not be used for a roof garden?

I couldn't see why not and the fibre glass would be a lot more hard wearing than torch on even put two 600gm/m2 layers on it to be 110% sure of no damage
In all fairness what are the engineer or architect been paid for. A flat roof is an integral part of the build why wasnt the build up ud the roof not speced out at the pricing stage or even before holidays were taken

jkavanag · 22-05-2019 4:36pm

Thanks guys, I dunno re the professionals but they have told me they dont get involved in insulation - not a lot I can do about that. The architect said use Trocal but you get varying reports and I have been told its not good for walking on. This is also the reason we were looking at a cold roof as well as the exorbitant cost. Everybody I have spoken to has given me a completely different view and the cost seems to be spiraling every time I talk to someone - the last guy wants to charge €5k plus VAT for a PVC membrane plus insulation - for a 7x5m roof. I posted here for some unbiased advice and to make some sense of it all. Thanks for your views.

Bullocks · 22-05-2019 5:37pm

jkavanag wrote: »

Thanks guys, I dunno re the professionals but they have told me they dont get involved in insulation - not a lot I can do about that. The architect said use Trocal but you get varying reports and I have been told its not good for walking on. This is also the reason we were looking at a cold roof as well as the exorbitant cost. Everybody I have spoken to has given me a completely different view and the cost seems to be spiraling every time I talk to someone - the last guy wants to charge €5k plus VAT for a PVC membrane plus insulation - for a 7x5m roof. I posted here for some unbiased advice and to make some sense of it all. Thanks for your views.

We have done a few jobs using trocal
and I'm happy with it. I think the last one I got done was about €105sqm +VAT including 80mm insulation.
-snip- roofing would be worth a call, they are the main trocal lads around Ireland I think
Bár the insulation I don't see why a cold roof would be a whole pile cheaper than warm and the insulation will have to be used inside anyhow aswell in a cold roof

Calahonda52 · 22-05-2019 7:38pm

https://www.nsai.ie/about/news/publication-of-sr-542014-code-of-practice

:eek: I dunno re the professionals but they have told me they dont get involved in insulation:eek:

What exactly does that mean?

jkavanag · 22-05-2019 9:35pm

It means they wont advise what I should do for insulation.

Bullocks · 22-05-2019 9:40pm

jkavanag wrote: »

It means they wont advise what I should do for insulation.

Thats not what you want to hear from an architect or engineer !

BryanF · 23-05-2019 10:21pm

jkavanag wrote: »

Thanks Sydthebeat.

I have paid for plenty of prof advice as it happens. The architect though is MIA because he was paid 6 months ago and isnt overseeing and the engineer is on his holibops for two weeks. The builder is just trying to save me money in fairness to him but I would veer to the safer side and insulate as best as possible. It seems to me that something like this should be fairly standard though.

So can you just confirm if I’m reading this correctly :

you paid for planning drawings. And Not an architects detailed drawings or supervision. Which means you are not entitled to an arch spec for the insulation or roof build-up. So the architect is not MIA, just did the job contracted and got paid.

The engineer is on is holidays and is probably only contracted to cover part A of the building regulations

Flat Roof Insulation

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