I'm building a house with concrete flat roof (20cm thickness, beamed & rebarred) with a total surface area of 190m2 (good waterproofing is taken care of).

 

Inside will be a plasterboard ceiling with plenty of LED down lights, fitted 20cm from the bottom of the concrete roof. 

 

I would like to cold roof insulate using SCG 7.5cm StayCool glass wool rolls. Warm roof insulation is unfortunately out of the question. I would like some advice on the best way to do so - using wooden joisting, do I fit the insulation snug to the bottom of the concrete roof? or fit the insulation with a 10cm gap from the bottom of the concrete roof? I am hesitant to lay the insulation directly over the plasterboard & the LED light fittings due to fire risk.

 

Any thoughts and advice is much appreciated, cheers !

Normally here they do a drop ceiling which is made of metal which can be any depth depending on the concrete roof height and plaster ceiling height you want.

 

As for downlighting under the insulation good luck with that, you can grin and bear it or do what im doing, ive phoned Phillips in BKK and they where useless, the English speaking service didnt know anything, asked for my phone number and said tech support would call which they never did a week later they emailed me a survey to fill out and I reminded them of there crap service which once again has not led to anything.

 

There are rated downright for sitting under insulation, no one in this country (Thailand) has a clue, even went to a shop that 90% of there business is providing lighting to the trades, boss man when asked, ho ive heard about them, then a blank...Home Pro and every other place I went did not have a clue, so you could take a risk as the battens will hold the insulation up at least 2cm so you would need those slim types and must be fully sealed with the what ever its called attached and not inside (the wiring gizmo) or as one person here suggested pot plant holders over the lights this would give plenty or air around the light, thats fine if you are just doing a few lights but im doing an entire house, near me and im in Pattaya is a lighting shop who have the Led slim line dome lights that fit simlar to downlights they have spring loaded clips that fit into a downlight hole about 2cm think and curved edges, unlike the ones ive seen at the HP etc they are much better looking similar size too a downlighting and thats what im going to go with.

If you have a flat concrete roof and a drop plasterboard ceiling, it should be fine. I believe insulation will do little to reduce the heat load. Coat the roof with a good, reflective sealer. 

 

If you really want to reduce the heat load, shade the roof. 

 

Heat rises. Cold air does not escape through the ceiling.