flat roof water pooling

[singhters]

hello all,

our kitchen roof is flat and has water pooling in one area near the drain is there anyway to eradicate this ? and after fixing a leak i was thinking to make the roof more leak proof by using flashing strip and a 2nd layer of felt roof ?

thanks all.

 

[alan333]

No easy answer to your pooling i'm afraid, you either need to lower the drain height or raise the rest of the roof.

If the roof's in good condidtion and sound there's no reason you couldn't add a new top layer.

 

[Xenon]

Ponding won't do it the slightest harm whatsoever.

 

[dann09]

singhters,

If its ponding then something is wrong. Typically, there are two "reasons" for ponding:
1. it was built to no, or incorrect, falls.
2. the boarding has slumped because its water damaged or its been incorrectly specified ie not strong enough. Or its incorrectly fixed.

you mention a leak, where was it located?

What kind of drain are you referring to: a drain in the field of the roof, or a drain at the edge of the roof?



I know that many roofers are accepting of ponding, often seeing it as a form of liquid insulation, or a minor failing .
I see it as a fault and a potential serious hazard. In commercial roofing, structures have been known to collapse from ponding, (we worked on repairing one) esp where the chutes and field drains have become blocked.
All ponding collects debris. Vegetable debris will work its way into any weak spot, it will also lift stones and grit.

 

[dann09]

I've just noticed that yesterday i responded to a 2012 last post - but how that happened, i dont know.
It was sitting near the top of the page in this forum - go figure?

 

[Nige F]

Worry not - you added some valuable points

 

[tony1851]

I think we've all done that sometimes!

 

[tony1851]

Although its an old post, someone mentioned that ponding on a flat roof doesn't matter; wrong - it does.

On a felt roof, during a sunny day, the felt under the water puddle always stays cooler than the felt which is dry and exposed, which of course tends to get warmer. The exposed felt then expands at a greater rate than the felt under the puddle . This repeated expansion and contraction (when the sun goes down) causes stress in the felt, which eventually tears and leaks, and it does so around the perimeter of the puddle.

 

[Xenon]

Although its an old post, someone mentioned that ponding on a flat roof doesn't matter; wrong - it does.

On a felt roof, during a sunny day, the felt under the water puddle always stays cooler than the felt which is dry and exposed, which of course tends to get warmer. The exposed felt then expands at a greater rate than the felt under the puddle . This repeated expansion and contraction (when the sun goes down) causes stress in the felt, which eventually tears and leaks, and it does so around the perimeter of the puddle.

On a roll of B n Q shed felt, yes. Modern HT felts will stretch their own length.