New flat roof - water pooling - is it normal?

user1168934

I had a new flat roof done a few days ago. With the rain this morning I have noticed water pooling on top of it. Most of it did flow off into the gutter but some stayed in the pool after the rain had stopped. The pool in the picture is roughly half an inch deep. FYI - the roofer has very good reputation in my area and I think he has been brilliant so far. I raised it with him and he says its normal. He tells me the roof has the correct tilt (2 inch I believe) that it cannot have more tilt because that would go against building reg. He has asked me to send some more photos once the rain has stopped which I will.

I have no experience with flat roofs before so I am just getting very anxious. Is this normal for a flat roof or is this something that needs to be fixed? How can it be fixed?

FYI - this is a new extension so it wasn't just a felt replacement. The whole roof including the underlying joists etc was done as part of this job.

shiraz99

Some pooling, particularly after heavy rain is fairly normal on a flat roof. However, if it's still there after 48hrs then I suggest you have an issue.

Having said that, looking at your pictures suggests the roofing isn't very uniform with areas of sagging and ripples. I'd be inclined to get them back in to have a look.

Section62

user1168934 said:

I had a new flat roof done a few days ago. With the rain this morning I have noticed water pooling on top of it. Most of it did flow off into the gutter but some stayed in the pool after the rain had stopped. The pool in the picture is roughly half an inch deep. FYI - the roofer has very good reputation in my area and I think he has been brilliant so far. I raised it with him and he says its normal. He tells me the roof has the correct tilt (2 inch I believe) that it cannot have more tilt because that would go against building reg. He has asked me to send some more photos once the rain has stopped which I will.

I have no experience with flat roofs before so I am just getting very anxious. Is this normal for a flat roof or is this something that needs to be fixed? How can it be fixed?

No, it isn't normal.

Whilst the overall fall might be 2", it is clear from the photos that the fall isn't uniform, it is obvious that some of the supporting boards have sagged and that is where you are getting the ponding.

A good roofer would have assessed the condition of the roof before refelting, and explained to you that merely recovering the roof with fresh felt wasn't enough - the underlying woodwork also needs attention.

Did he do that?  Did he give you the option of having the roof stripped back and reboarded?

If the felt has been applied properly then it should form a waterproof layer and some amount of ponding won't be an issue.  But if the felt has been poorly applied or breaks down over time, the ponding will make it more likely you'll get leaks into the roof structure and further problems.

As a general point, the overall quality of the work is poor (e.g. the wrinkles/creases)... so I wouldn't expect the roof to last very long before it needs more attention.

Unfortunately the art of laying a good felt roof is dying, and these days even roofers with a good reputation go around doing poor work.

user1168934

FYI - this is a new extension so it wasn't just a felt replacement. The whole roof including the underlying joists etc was done as part of this job.

shiraz99

user1168934 said:

FYI - this is a new extension so it wasn't just a felt replacement. The whole roof including the underlying joists etc was done as part of this job.

Looks like a pretty poor job then.

What direction is the fall on the roof in the first picture. On closer look at that pic it looks like the edge of the roof along the top right edge is actually curving slightly upwards, although this could be just a trick of the photo.

macman

That puts an entirely different perspective on it. You just said 'I had a flat roof done', 
It looks appalling. The pitch may be correct, but it's uneven and rippled. Whether that is due to poor joist or board fitting or poor felt laying is immaterial if it's the same contractor. I would not accept that as 'normal'.

Bendy_House

User, was there anything restricting the roof slope to just 2"? For example, was that house-to-extension-roof flashing line already in place from a previous roof?

If no restriction, then I wonder why it was set at that minimal slope in any case - unless that would have made the extension height a silly inch too high for PP?!

Anyhoo, that is poor. The builder should actively WANT to redo that - how can they possibly be happy with it? 

FreeBear

user1168934 said:  He tells me the roof has the correct tilt (2 inch I believe) that it cannot have more tilt because that would go against building reg.

Building regulations cover things like insulation, weight & wind loading, but not pitch (for a flat roof). The recommended minimum finished pitch of a flat roof should be 1:80, although a steeper pitch is perfectly acceptable as long as the gutters & drainage can cope with the increased flow. For a new build (or extension), these details should be designed in by the architect when providing the working drawings.

Pooling is to be avoided as it can increase the static weight loading, as well as serve to collect dirt & debris in the hollows - It also increases the maintenance burden and could shorten the life of the roof.

user1168934

Bendy_House said:

User, was there anything restricting the roof slope to just 2"? For example, was that house-to-extension-roof flashing line already in place from a previous roof?

If no restriction, then I wonder why it was set at that minimal slope in any case - unless that would have made the extension height a silly inch too high for PP?!

Anyhoo, that is poor. The builder should actively WANT to redo that - how can they possibly be happy with it? 

No, there was nothing restricting it. There was no previous roof or existing flashing or a silly height thing.

user1168934

What should I be asking the roofers to do now? How do we fix this?

He is coming to have a look tomorrow.

Bendy_House

user1168934 said:

No, there was nothing restricting it. There was no previous roof or existing flashing or a silly height thing.

That's worse, then - there is no excuse at all. I mean, even an uneven roof would be able to drain freely with a couple more inches of slope.

I think that the flashing has, at least, been positioned high enough to allow for a raised end there. But, of course, that isn't the cause - it's all down to the roof being so uneven, and there is simply no excuse for that. None.

The fix? It needs stripping, 'levelling' (ie, a straight slope), and recovering - with no wrinkles.

I really hope the guy will accept all this when he sees the roof and/or your pictures. Be ready to be matter-of-fact, ideally by asking - and therefore making them answer.

"I can see visible dips and ridges - should they exist on a brand new roof?" "There are a few wrinkles in the felt covering. I am sure that isn't normal - is it?" And find out why 2" was deemed enough, and more would break regs.