So I am having a house build with a flat concrete roof and was wondering if putting in a radiant barrier would be a good idea. In the past I have build houses with a sloped roof and always put the aluminium foil under the roof battens which helped a lot in keeping the heat out.

I still have a few rolls of the thin foil left but if there is a better material for flat roofs i won't mind buying that. I have seen the bubble foil but not sure if that is effective.

Edited February 24, 201610 yr by pokerkid

On my top floor (flat roof) condo I did put two layers of the this foam covered with metal film on the ceiling gypsum board.
The room seems to be several degrees cooler than the neighbours'.

On my top floor (flat roof) condo I did put two layers of the this foam covered with metal film on the ceiling gypsum board.

The room seems to be several degrees cooler than the neighbours'.

you mean the metal film with rockwool or PE like in this picture

I put the PE-foam product with foil shielding, similar to the picture, because could not find the fireproof Rockwool that I prefer, and do not like to work with the glasswool that seems to be preferred on the local market.

When trying to set the PE-product on fire, I noticed though that it does burn, slowly but steadily and quite smelly.