Pooling water on felt cold-roof with insufficient slope - Help!

[Kingo206]

Hi everyone,

I'm back again needing some advice on my extension roof. We've got a felt cold roof installed, but the firing strips are too short, leading to an inadequate slope and water pooling.

Initially, I thought adding a channel at the edge would drain the water into the gutters, but one roofer thinks this won't work and suggests overboarding with EPDM.

This essentially means building a new roof on top of the existing felt, which would leave the felt roof acting as a vapor barrier, but the cost is around £3.5-4k.

I'm a bit confused about the best solution here:

- Would a channel actually be effective in addressing the pooling issue, or is it a temporary fix at best?
- Is overboarding with EPDM the only long-term solution?
- Are there other options to improve the drainage without completely rebuilding the roof?

Any thoughts or experiences you guys have would be greatly appreciated!

I've attached a couple of photos to give you a better idea of the situation:

 

[Deluks]

Don't worry about it.
Next time it rains, the new rain will push that old rain into the gutter. Problem solved!

 

[Harry Bloomfield]

I'm back again needing some advice on my extension roof. We've got a felt cold roof installed, but the firing strips are too short, leading to an inadequate slope and water pooling.

I'm not a roofer, but to my eye - that looks absolutely fine, for a flat roof. You cannot expect all traces of water, to instantly drain away, unless you have a very steep slope on the flat roof. Then it wouldn't be flat.

 

[Kingo206]

I agree with you to an extent about flat roofs in general, but this looks like 'significant' pooling to me though, and it looks as though the weight has slowly began to cause the roof to sink overtime. The roof is approx a year old.

Here is an image of the roof on application of the first layer of felt. Note: we initially wanted to do a parapet roof hence why the external wall was above the roof. However, neighbours were understandably not too happy.

You can see from the image, the slope is perfectly fine until the point that sinks in and then levels off.

 

[freddiemercurystwin]

I'm not a roofer, but to my eye - that looks absolutely fine, for a flat roof. You cannot expect all traces of water, to instantly drain away, unless you have a very steep slope on the flat roof. Then it wouldn't be flat.

No a flat roof that has standing water has inadequate falls, whilst a roof may be called a flat roof it must still have adequate falls, minimum 1:80. The definition of a 'flat roof' is one with a pitch that has a pitch of 10 degrees or less. There is such a thing as a Zero Falls Flat Roof where you might try to achieve a dead flat roof or one with less than a 1:80 fall but this is not one of them and you would never build one in this scenario.

Nevertheless @Kingo206 I wouldn't worry about it, at least the laps are going the right way.

 

[Kingo206]

No a flat roof that has standing water has inadequate falls, whilst a roof may be called a flat roof it must still have adequate falls, minimum 1:80. The definition of a 'flat roof' is one with a pitch that has a pitch of 10 degrees or less. There is such a thing as a Zero Falls Flat Roof where you might try to achieve a dead flat roof but this is not one of them and you would never build one in this scenario.

Nevertheless @Kingo206 I wouldn't worry about it, at least the laps are going the right way.

Thanks for the feedback @freddiemercurystwin.

Are the laps actually going to right way though, this is the final position of the roof in the image below for clarification.

So you wouldn't be concerned re: the standing water, particularly given the amount of pooling that's there?

I just don't want it to be a situation whereby, I could've spent £500 to do something, than having a leaking roof and having to fully replace the roof in a couple years time.

 

[Ivor Windybottom]

I put a couple of nice gobby coats of Black Jack on mine...

Black Jack 905 All Weather Roof Coating - 25 Litres | Roofing Superstore®

This 25 litre can of Black Jack all-weather roof coating is a solvent-based full-bodied brushable bitumen compound with additional fibres for reinforcement....

www.roofingsuperstore.co.uk

I paid more for a number of 5 litre cans, as I didn't fancy lugging that thing around and up a ladder.

The stuff's like black sticky porridge, has reinforcing fibres in it.

Rinse with hosepipe, leave/wipe to dry then daub it on.

followed by a coat of silver about a fortnight later after it set...

Aluminium Solar Reflective Paint - Black Jack (907) - 5 Litres | Roofing Superstore®

A fast-drying, thin bituminous-based aluminium protective paint, this 5-litre tin of Black Jack Aluminium Solar Reflective Paint is ideal for a range of app...

www.roofingsuperstore.co.uk

Probably frowned upon by the pros, but seems like a reasonable precaution to me, plus I found that it instantly gets less hot in the summer, made a huge difference. After 5 years just lost some silver where the water gathers so I over-coated with just the silver this time. I'll probably use more black next time, in another 5 years.

I did mine while the felt was new, it should last for ever as the felt itself is sealed in and doesn't see the weather at all.

 

[Deluks]

If it doesn't leak now then there's no reason to think it will leak until such time the felt has aged to a point where it will need replacing anyway.

 

[freddiemercurystwin]

I don't really understand how you can add a channel drain to solve it? If you paid someone to do this and they've built inadequate falls then they should be putting it right/hanging their head in shame but that's another story. It'll be fine as mentioned by Deluks. Certainly no need to paint a load of gunk over it.

 

[Kingo206]

I don't really understand how you can add a channel drain to solve it? If you paid someone to do this and they've built inadequate falls then they should be putting it right/hanging their head in shame but that's another story. It'll be fine as mentioned by Deluks. Certainly no need to paint a load of gunk over it.

Thanks for the replies @freddiemercurystwin and @Deluks ! To clarify, when I said "channel," I didn't mean a separate drainage system. I was thinking would creating a slight dip or groove, by cutting the plywood down a level or so, near the edge of the roof, then layering felt over it to create a smooth slope towards the gutter in the problem areas. Similar to this:

> Do you think this could be a viable solution, or would it likely cause other issues down the line?

I appreciate the input about the original roofer. It's frustrating, but I'm trying to focus on finding the best way to fix the problem now.

 

[Deluks]

What you propose will guarantee you a leaky roof.
If it ain't broke....

 

[freddiemercurystwin]

This:

What you propose will guarantee you a leaky roof.
If it ain't broke....

 

[noseall]

Thanks for the replies @freddiemercurystwin and @Deluks ! To clarify, when I said "channel," I didn't mean a separate drainage system. I was thinking would creating a slight dip or groove, by cutting the plywood down a level or so, near the edge of the roof, then layering felt over it to create a smooth slope towards the gutter in the problem areas. Similar to this:

> Do you think this could be a viable solution, or would it likely cause other issues down the line?

I appreciate the input about the original roofer. It's frustrating, but I'm trying to focus on finding the best way to fix the problem now.

Your roofs fine. Worry about something else.

 

[Kingo206]

Thanks for the input all. I appreciate it.

Although it is worth mention, in the original post, the roof with no water is when the roof was newly finished.

The roof with the standing water is a year or so after installation. The standing water has progressively increased I feel, but I will keep an eye on it.

 

[Notch7]

No a flat roof that has standing water has inadequate falls, whilst a roof may be called a flat roof it must still have adequate falls, minimum 1:80. The definition of a 'flat roof' is one with a pitch that has a pitch of 10 degrees or less. There is such a thing as a Zero Falls Flat Roof where you might try to achieve a dead flat roof or one with less than a 1:80 fall but this is not one of them and you would never build one in this scenario.

Nevertheless @Kingo206 I wouldn't worry about it, at least the laps are going the right way.

My understanding is that a fall of 1 in 80 is a minimum fall, but for a felt roof the fall should be 1 in 40 which allowing for seams and bowed joists will end up as 1 in 80 as a minimum