Building Control Approves 2″ of Celotex Insulation on Flat Roof

Hi Steve

I’m a keen diy enthusiast building a single storey one room (lounge) extension. I am going to have a rubber membrane flat roof and have been doing some research online. Your videos crop up in the search results frequently. I must say – thanks for the information, it’s great that people like yourself aren’t afraid to pass on your knowledge.

I’ve been trying to find the definitive answer to the best way to create a warm flat roof that isn’t too tall, but there are so many conflicting views! I live in the midlands and I’m looking for a bit of advice (concerned about doing the wrong thing), is it possible to pay for your advice via email?

My building control officer says it’s all right to place 2″ of Celotex insulation that won’t need a vcl because of the foil, straight on to the furrings, then a ply/osb deck and EPDM membrane on top. And then place some Rockwool or more Celotex in between the joists/furrings against the underside of the main Celotex slab. I can’t find any examples like this.

The other thing I can’t find out about – our roof will overhang the building by a meter or so, so should I finish the cavity wall insulation up to the underside of the main roof insulation and then start fresh pieces of Celotex for the overhanging portion of the roof or not have any insulation in the overhang?

Would be great if I can get your advice but I fully understand if not. Please drop me a line if you can’t help just so I know.

Many Thanks