On Thursday, 13 September 2018 21:14:29 UTC+1, Mathew Newton wrote:
We have just had the shell of an extension built which includes a flat roof. Firring strips have been used to produce a fall to one side however this fall is around 20mm over the 3000mm span i.e. 1:150.

Everything I am reading states that, as per BS6229, flat roofs should have a minimum fall of 1:80 (i.e. 37.5mm in my case) and really ought to be designed for 1:40 (75mm) to allow for inaccuracies in construction, settlement of materials etc.

Unfortunately I have only just spotted this and the roof covering (consisting of OSB sheets, vapour barrier, 125mm solid board insulation, ply and a polyurethane liquid membrane) along with cavity trays and flashing all now in place.

Now I'm fretting about possible issues in the future. Am I right to be worried? Should I be seeking this being altered? I was going to speak to Building Control tomorrow to say what they say but whilst they might confirm the fall is low I can't see anything in the regs that mandates a fall and I don't know whether BS6229 is mandatory either (it seems more of a code of practice).

Grateful for your thoughts.

P.S. For what it's worth I must admit to having a tendency to worry - to the point of anxiety - about detail like this.

IIRC some of the first flat roofs were fully flat with a lip all round. The intention was they held a thin layer of water which somehow protected the felt. Needless to say that method was replaced, the first slight hole and it all went in there.

I don't see BR helping you.


NT