Mathew Newton Wrote in message:
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.


How much of an upstand is there against the "host" wall?
What are the chances of water building up on your flat roof to
overtop the upstand?
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Jim K


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