New build roof & dormer window rainfall query

Hi there,

We moved into a new build a few months ago.

Almost straightaway we noticed that when it rains, the water from a large section of roof, streams over the top of the box dormer windows to the ground (right in front of the garage entrance doors).

It doesn’t seem right to us and we’re trying to get a response from the developer, but after at least a month we haven’t heard anything back.

To us, it seems like there’s not enough guttering to sufficiently take away the rainfall that collects on the roof above, as it’s quite a large area. There’s effectively just two short sections of guttering for each side of the roof which is large. The rest just flows over the dormer windows where the guttering isn’t.

As well as having rain water streaming in front of the dormer windows when it rains, this is causing the wall and door area below to get damp. We’re concerned that the water could affect the foundations in the long run too. Also, we want to make sure the dormer windows are ok so they don’t leak in the future.

Just wondering if anyone has any tips on how the roof should handle the rain fall and are we actually correct in thinking that most of the rain should be taken away by the guttering rather than pouring on to the ground and walls below?

One solution we have thought of is if an extra section of guttering was installed below the last roof tiles before the rain hits flat roof of the dormer windows. Would this be a good idea? This is the blue line on the second picture.

Does anyone have any tips about how to calculate if the gutters are adequate for the roof and rainfall?

Or if it meets the building regs / control?

Thanks

Not surprised really its a bad design.

That’s what we were thinking. Any ideas how we can find out what would make it handle rainwater better?

We’re happy to get a specialist to have a look and advise but not sure who’s remit this would be covered by? A surveyor/architect/roofing contractor?

Get rid of the small window that interferes with guttering and I am sure things will improve, because that's how 99% of houses are built!

Get a lead worker to burn an upstand across the front. You may need to return the gutter into the two lead cheeks to help it cope .

catlad said:

Get rid of the small window that interferes with guttering and I am sure things will improve, because that's how 99% of houses are built!

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Too true!

datarebal said:

Get a lead worker to burn an upstand across the front. You may need to return the gutter into the two lead cheeks to help it cope .

Click to expand...

I’m just thinking could maybe putting a tub of guttering approx where the blue line is in the photo be a possibility? If it is, then the gutter should divert most of the rainfall down in to the side gutters and away. The smaller amount of rain water that will still flow forwards over the window would be manageable and significantly reduced.

If the lead is made to stop water flowing forwards over the top, even if the side guttering is put into the lead cheeks, then would it make the back part of the flat roof more vulnerable to water ingress? If not now then over the years?

Just also trying to work out how the dormer window is supposed to cope with rainfall? Like is it actually not working as per the design? What should this type of roof do with rainfall?

*run not tub

Yes you could run gutter across the front edge , the existing will still need to be extended around the corner.
Stopping the water running over the edge making it run sideways should be fine .

It may be possible to raise the lead and fit a slate baton under the lead to help stop the rain flowing over the edge.

datarebal said:

Yes you could run gutter across the front edge , the existing will still need to be extended around the corner.
Stopping the water running over the edge making it run sideways should be fine .

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Thanks for your reply. We were wondering about putting the guttering along the back edge of the dormer lead flat roof, so that it would be positioned just at the base of the last roof tiles, to collect and divert rainwater away. Would this be an option rather than the front edge?

catlad said:

It may be possible to raise the lead and fit a slate baton under the lead to help stop the rain flowing over the edge.

Click to expand...

Thanks for your reply. That sounds good too - in practice, where would the rainwater get taken / diverted too? We kind of want to avoid taking it to the back of the flat roof and more to the sides and down into existing guttering.

CazDIY said:

Thanks for your reply. We were wondering about putting the guttering along the back edge of the dormer lead flat roof, so that it would be positioned just at the base of the last roof tiles, to collect and divert rainwater away. Would this be an option rather than the front edge?

Click to expand...

I doubt it would sit nicely , and any bracket would need to be screwed through the lead.

datarebal said:

I doubt it would sit nicely , and any bracket would need to be screwed through the lead.

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It’s hard to show in the photos, but there seems to be a vertical gap between the bottom of the roof tiles and before the dormer flat roof starts. To the untrained eye it looks like it’s just a gap but there could be timber visible too. It was in this gap I was wondering about adding guttering in…It does seem like there could be space potentially.

That was going to be another question for the developers…if the gap between bottom of the roof tiles the lead dormer flat roof is watertight too.

The lead roof will extend up the roof slope under the tiles. There will not be anyway of fixing the gutter without going through the upstand