Flat roof insulation

Loft insulation should be about 250mm. So if you work by the same principle.

But about as much as you can fit in would be ideal.

And leaving around 200 to 300 mm around the spot light positions, and an air gap to allow ventilation of the heat away from them. In fact, does a kitchen ceiling really need to be insulated fully?

Remembering it's the air trapped in it that is the main insulator - don't pack it in tight, let it sit loosely.

If you compress it all up it's way less effective.

No. As thick as you can get it.

yep it does.

Usual clueless nonsense...

Dr. Drivel, usenet posting "As thick as you can get it"!

Since the flat roof is (I assume) already sat straight on the tops of the firings (or perhaps even the rafters), you don't have the option of a warm deck construction (i.e. with insulation above the woodwork, but below the roof substrate).

This basically leaves the option of stuffing the space between the rafters. Hopefully water should not be getting in from outside the roof, so there is less need to arrange ventilation of the roof timbers (as there would be in a loft for example). Most moisture that gets there will be coming from the kitchen. Hence a foil covered PIR board (like Celotex, Kingspan, Ecotherm etc) cut to be an interference fit between the rafters would be the simplest way forward. A whole lot nicer to work with (and more efficient) than the traditional rockwool type products.

You may want to opt for fully reflective bulbs (i.e. not dichroic) to ensure not too much heat is allowed to pass back into the ceiling void.

Isn't this also a situation for those back cover thingies - the type that fill with foam and seal the spot light fitting to prevent fire bridging? Not sure how possible these are to fit with no loft access mind!

Phil

This is a *flat* roof we're talking about!

Leaking is what they do :-(

I repeat. "As thick as you can get it." It is cheap and easy to install too.

Best to use high performing Kingspan foam insulation in case of water ingress.

No it aint.

I've got a flat roof which I had re-done with a fibre glass roofing system and a 25 year guarantee with it. It's miles better then the tar & felt option which we still persevere with since Roman times.

On 11 Jul 2005, RedOnRed wrote

I don't think the Romans had many flat roofs in the wet colonies -- very shallow-pitched ones (with tiles), yes; but flat?

(And if they did, I suspect they used a lot of lead instead of tarred felt. They were big on lead, were the Romans. And it's still a fairly unbeatable covering for roof flats.)

I had my garage done the same - been great ever since. But every flat roof I've ever had has needed something doing to it. Damn things.

Probability says that unless the roof has already been redone, leaks *will* be a problem and the choice of insulation should take that into account.

I should have said tar and felt technology which, before you start on about how they didn't use felt from Wickes or something back then, has basically been in use since Roman times in one variation or another.

Hope that makes things clearer for you.

An Intumescent hood?

These are designed to maintain fire break integrity. They don't do anything to allow the lamp fitting itself to cool however - you still want some space round them

Doable, they fold up to allow you to get them in there...

And just what size joists do you imagine the average flat roof on an extension has?

When I has something like this done, the architect wanted to leave a free flow of air to the joists and roof plywood base. So he specified 4" polystyrene between joists and plasterboard. Of course you lose some ceiling height.

A general response to general comment. Obvious to the intelligent, but not to you. Sad but true.