Flat Roof Vent Leak

8 Sep 2011
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United Kingdom

I have a slightly sloping (1/60) flat roof with a velux atrium. Where the roofing felt has been overlapped it traps water from moving across the slope and the window stops the water from flowing down the slope.

The resulting pooling of water then creates splashing and the water splashes up into the air vents along the brick and roof join. I now have a leak inside where the water is dripping down the vents.

The builder has put a lead 'curtain' from the roof surface up to the vent to stop splashing. This curtain is covering the vent just by the pooling water and covers about 30% of the entire vent. I thought this was okay as the ventilation will still be okay.

However, after the very heavy rain this week there is another leak on the same scale. The builder has suggested putting a lead curtain accross the whole vent now and i am worried this will cause more problems due to condensation from poor ventilation.

Should i take his advice?

I was thinking doing the curtain to stop the leak in the short term, and work on getting rid of the pooling water so it doesnt splash up.
I need to raise the level of the roof slightly so it flows across the slope until it moves from behind the roof light, it can then flow down the slope away into the gutter. How can i do this? I was thinking liquid rubber and sand to make a trowelable material into a slope?

Or can i cover the vents with anything to stop the water but keep the air flow?

I hope that makes sense. Any suggestions would be appreciated.


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No replies because your post is so confusing. I would suggest you take a few photo's and upload them.
What sort of vent is it behind the "lead curtain". Can you indicate size and how far above the felt roof the bottom of the vent is?

Do you get any leak from the large pipe penitration ?

Normally a little pooling of water on a flat roof is not a problem, however It is never good to have it pooling around penitrations, as this is a often a problem area.

If spashing water is the problem and it gets into the vents. One solution would be to make up a small section of a false roof over the vents with open ends sufficent for the required airflow. Similar idea to your lead curtain but on a larger scale, and allowing venting from the ends rather than a small low gap at the front.

It may be possible to build up the level of the ponding area of roof by applying additional layers of felt. I'm not sure on this one and hopefully a roofer may be able to advise.
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