while ripping down my ceiling for my kitchen extension to do a bit of electrical work i have discovered that there is no insulation in the roof.What is the best optiion for this - how thick do i need it and what is the best to use bearing in mind that i am putting up spots
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?
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.
100mm would probably be overkill, as little as 50mm would make a big difference... (especially when you consider the problem with many kitchens is getting the unwanted heat out of them!). It would also leave a bit of air space round the spots to stop them overheating.
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!
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.
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 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.
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...
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.
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