Contractors: How much to expect

[Fitzroy]

I've just had two flat roofs replaced, both with EPDM, at the advice of the roofer. The front roof is above a bay window, which is sunken c. 2 inches below the level of the stone work of the bay. The old roof used to collect water, which the roofer advised was bad, and in his quote included:

2. Re-board using 12mm OSB redirecting water if there is not sufficient “fall” on roof".

It's just finished raining and the new roof has a pool of standing water on it! I've not paid yet and wondering, does it matter to have standing water on EPDM, it feels unreasonable to ask him to try again as it would need all coming off. Thoughts very welcome.

Fitz.

 

[sunnybob]

If the roof is truly flat, then youre never going to clear it of all water.
How deep is the puddle? If its a half inch or less then I would accept that. I had a very large flat roof on one house, and it was covered in gravel. When I asked the question, I was told the gravel helped to trap the water, and stop the material drying out in the summer.

I'm, not a roofer, but that was what I was told, and when I had to have it re roofed after 20 years, again gravel was laid on it.

 

[Zeddedhed]

If EPDM has been properly laid then standing water is not a problem - in Germany it's not uncommon for the outlets on flat roofs to on an upstaged so that the roof remains underwater. Helps to keep it cool and minimise expansion/contraction.

 

[Woody2Shoes]

Hi

as I remember, the definition of a flat roof is anything with a pitch of less than ten degrees. I don't think that the odd small pool of water is an issue.

Two things in your post made me wonder slightly:

1) 12mm OSB seems a bit thin - I'd have used 18mm (and probably have used OSB3 not OSB2 for good measure)

2) If he said he would lay it to a fall, he's obviously failed rather badly (unless it's sagging because it's only 12mm and poorly supported undernaeth I suppose)!

Probably best not to worry (for another few years anyway), cheers, W2S

 

[finneyb]

If its holding water I'd have him back, standing water will find a way through eventually and he did himself advise it was bad.

Brian

 

[stevep]

EPDM is commonly used for gaskets in between flanges for pipe work, so a little standing water shouldn't be a problem.

 

[RobinBHM]

I think flat roofs should have an effective fall of 1 in 80, which in practice means setting firrings at 1 in 40. The steeper fall then allows for seams in felt roofs and inaccuracies in the joisting and firrings.

Is the standing water caused by a seam thickness or a lip around the outlet or shoot? Thats quite a common reason. A small amount of ponding if fine, roof joists can sag or be a bit warped.

12mm osb was probably laid as an easy substrate for sticking the epdm to. It is too thin to be used to correct falls. Was the roof stripped or just overboarded?

In theory an epdm can have a very long lifespan even if under standing water -after all epdm is used for ponds!

 

[John933]

I've got a flat roof as well. But to me a flat roof is not flat. Always has a run off. Don't ask me what mine is, but it's enough to do the job. I had problems with mine. Thought I would repair it. Did not work still leaked. Got on e bay. Drove down to London, north circular. Picked up three roll's of really heavy duty felt for a good price. With six roll's of light weight stuff. Took all the stones off. Then tacked two thin layers down, or more one thin and one a little thicker. It's common sense in how you put it down. Tip. Get a warm day measure the length you need. Roll it out on the lawn, cut it. Let the sun warm it up. Roll it up and get it on the roof. Then tack it down. I cut about four lengths at a time, each one warming in the sun. One or two of them you have to cut down the length the make half widths. It's for the over lap. But you will work it out. Then I got my self a bottle blow lamp from a mate, or a car boot sale. With two of us. We got the top layer torched down. I did not take the old layer off. Just cleaned it up, and layer on top. So now it got about six layers of felt up there and stones. That woun't leak in a long time. If it's going up against a wall. You will need to dig out some cement to feed an end in. I then took the next course up and dug out some more to put a small pice in for a over drip. When it's all done. Wait a week or so. Then get up there with a mastic gun, and finish off the wall seals.
Hope that help's.
John933