1 degree slope flat roof & zinc batten roll

[luz624]

Hello, we have a small part of flat roof, by our side return extension - about 3m x 1.5m (the rest of the extension roof is pitched). It's been built with a 1 degree slope, along the 3m run. I know zinc standing seam requires min 3 degree slope. A contractor suggested we could go with batten roll, which would help to avoid water ingress at the seams. 

 

Does anyone think this would be OK, or better to re-do and add a greater slope?

[markc]

Zinc doesn’t “need” a 3 degree slope, as long as the water does not pool higher than the seams then it will be waterproof.

[Ajn]

The question can't be answered unless it is known where the water on it will be comming from. Is it just the sky or is there other runoff? What is your peak rain fall? How does it drain, one side or one corner? What is the height of the seam? What is the distance between the seams.

 

Heavy rain will cause the water to pool (get deeper) where is is running against an edge (seam) due to resistance. Such pooling can be significant.

 

It can all be calculated but a bit of thought is enough...

 

 

Edited February 6, 2022 by Ajn

[joe90]

Call me a pessimist but I always like a slope. ?‍♂️

[Dave Jones]

is it a warm roof ? use tapered insulation ?

[tonyshouse]

1:40 min

[PeterW]

3x1.5m  at 1° (assuming the slope is the 1.5m direction) is around a 26mm lift on the back edge. For 3° you need about an additional 52mm so the simplest solution is to get the contractor to fit a 50mm square batten along the wall edge, then a 25mm thick batten at 750mm and then re-skin the roof in 18mm OSB, screwed to the battens and the front edge. It’s 2 sheets of OSB, and 10m of standard roofing batten if he doubles up the back and it will go nowhere. 
 

Total cost is about £60 and an hours labour - ripping the roof off for that is not worth it.