New flat roof level and holding water?

[Inthedarkcustomer]

Hi,

We have a new flat roof on our extension, approx 3m X 6m

When it rains it takes about 5 or 6 hours for one half to drain away, does this sound right for a new roof?

I went up with a spirit level and where the water sits it is perfectly level, I've taken a picture of the level in the middle of a straight 2.4m length of wood running towards the guttering, as you can see it reads level! I've read it should be 1:40 or 1:80, what would that look like in a level?

All advice appreciated

 

[HERTS P&D]

Shouldn't your level be the other way round?

Andy

 

[Inthedarkcustomer]

The level is running along the roof towards the guttering? The top of picture is towards the wall and the bottom towards the guttering if the makes sense!

 

[HERTS P&D]

The level should be on the thin edge, so you can see the bubble from above.

Andy

 

[Inthedarkcustomer]

Oh sorry! I did try it on thin edge and the bubble completely level, as as this picture!

 

[^woody^]

Short answer is that yes, it should drain and not pond.

It depends on what you actually asked for and paid for, for this "new roof".

Also relevant is how much is actual ponding, or if it is mainly just damp residue.

 

[Inthedarkcustomer]

Thanks woody, the builders were commissioned to built the single storey extension with a flat roof, the water puddles on that half for about 5 hours, the other side drains within an hour?

 

[Inthedarkcustomer]

Sorry, to add, this a new flat roof built by the builders as part of the extension, less than weeks ago

 

[^woody^]

Oh well, for new work it should be better. The standard would be for it to be free draining with no ponding. And there was no reason why this could not be achieved with new work. It's a quality issue alright.

Depending on severity, it might not be worth requiring it to be redone, rather negotiate a cost reduction based on the fact that the roof's life is now reduced. And it won't get any better. But if the builders won't mind redoing it, then go for that - it would certainly be within your rights, and the contract if you pushed it.

 

[Inthedarkcustomer]

Thanks woody, I expected a new roof to be free draining. Do building control not check the slope is adequate? It hasn't been signed off yet by building control, should I push them to highlight it?

 

[^woody^]

No, building control wont be interested. All they will be bothered with is that its weathertight, has enough insulation, has ventilation if needed, and if the covering is suitable in terms of fire spread if near to boundaries. Thats it, they are not quality inspectors.

 

[chappers]

Ideally it should be pitched at 1:80 minimum, but you say it is eventually running away. The Germans build their flat roofs flat and allow water to pool on them. your main problem will be a rapid build up of unsightly algae.
As woody says there is no reason why they shouldn't have put an adequate fall on a new roof though.