New flat roof has standing water (+link)

[oddjobboy]

I've just had my flat roof replaced with traditional tar/felt and yet it's still not draining properly.

Overall I'm happy with the quality of workmanship but the roofer who surveyed my house prior to doing the job failed to pass the message onto his team that an extra 2inches of fall was needed.

I'm now at the stage where I need to pay for the roof, but I'm not sure whether the work that's been done would be considered up to scratch.

Should I go to the expense of getting a surveyor to give his/her professional opinion?

Or is a half inch of standing water considered acceptable?

Any thoughts very much appreciated.

3.4MB Quicktime movie of what I'm talking about here:

[Nigel Molesworth]

A flat roof doesn't drain.

[sm_jamieson]

Huh ? I would never have a flat roof that was actually flat. I remember a grand designs, where they fitted this fancy german standing-water type of roof. And guess what - it leaked. I "flat" roof should always have enough fall for it to drain. Your surveyor / workers messed up. Are they the same company ? I would not accept the work. Simon.

[tony sayer]

In article , oddjobboy writes

Thats his fault then, and they should rectify that at their expense. From the vid looks like the edges could be raised a bit too, so the water doesn't go over the edge during downpours IMHO.....

I don' think it is not with puddles like that all due to insufficient fall..

I'd point it out to them all in writing of course, and threaten that you are going to take pro advice..

No..

[TheScullster]

"oddjobboy" wrote

Couldn't open the video!

Last year we had a flat roof removed and replaced with tiled pitched version, but:

The flat roof that was removed included tapered pieces of wood to create a "fall" (I think these are called firrings - sp?) The high side and end of the roof also had a ridge close to the edge so that water would - in theory - drain off the roof along one side only. Hence guttering fitted along low side only.

So....flat - yes ...........level - no.

Phil

[Phil L]

Of course it does because it's not flat, it's supposed to be sloped, although this one isn't. Also he's done it all in green mineral felt which is bad. It's supposed to be smooth and have a couple of coats of reflective (aluminium) paint - once the sun gets on that it will be a mass of bubbles, which will then burst and he'll have to start all over again.

My advice is not to pay for it, tell the roofer it needs doing properly, with another 2-3 inches of fall and finished with a reflective finish.

[Chris Bacon]

Perhaps that would have made the job too expensive. What were the specifications? It should have three layers. Was the deck replaced?

It looks OK, a little clumsy in the detail, but OK...

Up to you. Have you a guarantee? Is it worth anything in terms of you being able to claim against the roofers in a few years?

That's not a problem at all. What *is* a problem is if some putz puts 2" of "chippings" up there.

do unless it's vital, either don't wear shoes, or wear very soft-soled ones such as plimsoles.

[Nigel Molesworth]

There is no requirement to put a pitch on a flat roof.

[David Hansen]

On Fri, 07 Apr 2006 11:40:48 +0100 someone who may be Nigel Molesworth wrote this:-

A "flat roof" should have a gentle fall to a drain, which can sometimes be identified by a gap in the upstand that forms the edge of the roof. Without that fall and drain, water would pour over the edge all the way round and seep into the walls. Some ponding is not a great problem, providing wind and sun will soon remove it.

Standing water, heated by the sun, is an ideal breeding ground for Legionella bacteria. These bacteria are present in the rain, though not in a high quantity. Heating them on a roof provides ideal conditions for the little devils to multiply rapidly and become a health problem.

[Phil L]

There are 'reducers', long lengths of timber which go from 3 inch (or whatever) to zero over their length, these are fixed to the top of the joists prior to boarding, this is what gives you the pitch, albeit a small one, about 1 in 30 in most cases, while the underside of the joists remain level for affixing the ceiling to. Whether it is a requirement or not is immaterial, the OP requested it and moreover any roofer worth his salt would have made sure there was adequate fall, especially with a roof like this, which according to the video, appears to be taking most of the main house roof water too.

[Rick]

You did get a written statement as to what would be done ?

Rick

[Dave Fawthrop]

|I've just had my flat roof replaced with traditional tar/felt and yet |it's still not draining properly. | |Overall I'm happy with the quality of workmanship but the roofer who |surveyed my house prior to doing the job failed to pass the message |onto his team that an extra 2inches of fall was needed. | |I'm now at the stage where I need to pay for the roof, but I'm not sure |whether the work that's been done would be considered up to scratch. | |Should I go to the expense of getting a surveyor to give his/her |professional opinion?

Flat roofs are never flat, they should have a slope of,IIRC from doing mine, 1:50

|Or is a half inch of standing water considered acceptable?

No

|Any thoughts very much appreciated.

Get the job re done. Call in Building Control, they will play hell.

[Dave Fawthrop]

|On Fri, 07 Apr 2006 12:49:19 GMT, Phil L wrote: | |>> A flat roof doesn't drain. |>Of course it does because it's not flat | |There is no requirement to put a pitch on a flat roof.

There was when I did mine 1:50 slope.

[Christian McArdle]

That's a new one on me. I've never even heard of a flat roof without a pitch. How would it be expected to drain?

Christian.

[owdman]

Oh yes there is Nigel - otherwise you will get standing water and leaks. Unless the roof is designed to take standing water which is unlikely, and would be very expensive to do properly. The op is going to have a lot of trouble with this roof and shouldn't pay the builder until it is put right i.e. with a fall of about 1 in 40 or more. Fall of less than this may become inneffective due to settlement etc.

cheers

Jacob

[Steve Firth]

Umm well I've seen wet roof construction used in many places and they definitely are designed not to drain. The roof of Leicester University library for example. There is also flat roof construction using butyl rubber sheet as an impervious membrane which means the roof can be made without a pitch.

A felted roof needs a pitch.

[Tony Bryer]

I wasn't clear from the OP as to exactly what the firm was contracted to do. IME (limited) the T&C for firms who just lay felt or asphalt say something to the effect that they take the falls as they find them.

[Phil L]

Hmm, 'the falls' are an integral part of the roof and need to run the right way for the roof to function normally. If he found that the joists or other timbers were rotted, or incorrectly placed, he should have informed the client and agreed a price as an 'extra'...also the OP says that he requested an extra 2 inches of fall prior to work starting, in other words, the contractor should have already priced this with the original quote but he hasn't done it...if it were mine I would have them back, I doubt that roof would last 18 months before it leaks in.

[oddjobboy]

Thanks everyone for helping me decide how to proceed with this. I've added a few pictures to further illustrate the standing water on the flat part of the roof.

thought it interesting that Dave suggested I call in Building Control. I wasn't aware there was a body I could turn to for support.

I suppose there'll be a fee to pay if I do go down that route.

This is all very frustrating because it could have been avoided if the decision to add the extra fall to the roof timbers had been communicated to the guys who eventually arrived on site to carry out the job.

[John]

I wouldn't pay a bean until you are satisfied with the work. Some of the pictures show a lot of standing water over joints so are potential leaks. As for the guys on site, if they're worth their salt and knew what they were doing, they should have known a fall needed to be made and not have to be told as much. Why don't you have a word with the roofer that did the survey and see what he has to say!

Cheers

John