Correct fall for flat roof - are regs still just 'encouraged'?

[TheDeuce]

Hi all,

I've designed and installed the timber work for a flat roof within a parapet wall on our self build extension. The fall is from the rear to a drain gulley at the front which exits through the wall in to a hopper.

The fall from back to front over a 3.4 span is 50mm to 0mm which achieves the minimum 1:80 (it's actually 1:68 which is all good) as I see the regs 'encourage'. That's all fine. However I've just realised that the gulley at the base of the fall which is 5.4m long itself only has a 50mm fall which 1:108..

I know this will work as I've checked it with laser level and there is no chance of deflection/settling as the gulley construction is bolted through to the block wall - so it's less than ideal but also is and will remain a consistent downward slope to the hopper. But... could it be a building control issue?

In the regs it's the word 'encouraged' 1:80 minimum fall which suggests that it's simply the home-owners issue if it doesn't quite achieve that. I thought I'd ask for the input of pro's on here just in case though! If really necessary I could remedy the fall along the gulley to just about make it meet regs but I'd rather leave it as it is and crack on with GRP.

NB: The design was based on what the architect specified so not just me seeking to cut corners. The architects original spec was for 50-0mm firings along the length of the gulley.

Thanks in advance for any input.

 

[rssteve]

Isnt it a 1 in 40 fall to achieve a minimum of 1 in 80 allowing for joist sagging over time and deflection. As long as the roof is waterproof it wont matter. I cant see the BC guy checking the levels anyhow.

 

[^woody^]

Yes, the roof will sag.

 

[TheDeuce]

Yes, the roof will sag.

'Yes' to what bit?

The roof will sag, they all do - but starting with the 50mm fall over 3m is that too little?

The 50mm fall along the 5.4 gulley definitely will not sag, it can't.

 

[TheDeuce]

Isnt it a 1 in 40 fall to achieve a minimum of 1 in 80 allowing for joist sagging over time and deflection. As long as the roof is waterproof it wont matter. I cant see the BC guy checking the levels anyhow.

Thanks.

That is indeed the wording/intent of the regs but the final test can only be if the finished roof achieves at least 1:80, whatever it was designed to achieve. As you say, it probably won't even get looked at anyway...

I just like to be correct by the regs for the sake of not worrying about criticism! In this instance the regs do appear to simply be advising good practice, so shouldn't be a BCO concern anyway, at least that's how I read it. Was hoping a pro would be able to clarify that.