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Flat EPDM Roof Terrace Leaking


steveoelliott

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Hi Folks,

 

I moved into our house 8 months ago... Before purchasing the house, when we were viewing the previous vendor had a leak (they were open about it and it was obvious). It was apparently due to an issue with the outlet and that was corrected prior to us moving in.

 

Around a month after moving in, we discovered some blown plaster on the wall downstairs that is beneath one of the parapet walls on terrace and a small water spot on the ceiling. A local flat roofer, took all the slabs off the terrace and filled with water and reckoned he couldn't find any leaks. The advice was then to re-lay the coping stones on both parapet walls and install a DPC underneath. This was completed in January 2020.

 

The room below stayed dry until we relayed the slabs recently. The slabs sit on plastic pads that are laid on a protective fleece. Following heavy rain we noticed a large water stain on the ceiling. In a series of experiments, I have identified that the leak seemingly only occurs (or is visible) when the slabs near the outlet are in situ. Removing a bunch of slabs together with pads and fleece near the outlet seems to stop staining on ceiling below. I can presume this is due to the water flowing off more quickly.

 

It is worth noting that following rain / me flooding the roof with water, it can be many hours before the staining appears.

 

The main reason I am here is I am looking for opinions on how to tackle this moving forward. I've had a series of local roofers visit to quote and these are options presented:

 

1) Inspect roof and lap another layer of EPDM over every seal.

2) Remove EPDM roof and replace with 3 layer torch on felt as 2 roofers said they don't touch EPDM /Rubber membranes; stating they are problematic / unreliable.

3) Paint over EPDM with some kind of liquid membrane.

 

All roofers quoting have stated that the up-stands don't sit high enough and that lead flashing should above (they are not present currently.

 

Personally, I want to replace EVERYTHING that it could be. This is not a cost saving exercise but rather one of ensuring I don't have further leaks / problems and the assurance of a proper guarantee. I am looking to replace the coping stones with aluminum copings as I want to avoid issues in future with the copings coming porous / mortar joints allowing water ingress.

 

I just want professional opinions on how best to address this. I am based in Kettering Northamptonshire, in case anybody happens to be local/ wants to quote :)

 

Below are a series of pictures, including the plans where terrace featured back from 2009 in case there are questions on materials etc.

 

Thanks in advance...

 

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Terrace Plan.jpg

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do you know the product used for the EPDM?

I've had one in a previous office where the manufacturer sent out an inspector to look - basically it hadn't been done properly, but the solution was to basically start again from scratch to make sure it was done to the manufacturers spec and then it got a guarantee on the work too

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I am sorry you are having this problem.  I think the solution is to strip what you have there and re-do.  Make sure the contractor is responsible for the whole job.  Done properly with quality products, single ply, built up felt, GRP and liquid applied all do an excellent job.

 

Go for a BBA approved system and a contractor approved by the system manufacturer.  Make sure they produce a proper approved design and spec for their proposals and do not accept any "by others" clauses.

 

The rainwater outlet does not look great.  Also I am not sure if there is cavity tray and weep holes just above the upstands.  Failing that a coat of Storm Guard on the brickwork above.

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3 minutes ago, Mr Punter said:

I am sorry you are having this problem.  I think the solution is to strip what you have there and re-do.  Make sure the contractor is responsible for the whole job.  Done properly with quality products, single ply, built up felt, GRP and liquid applied all do an excellent job.

 

Go for a BBA approved system and a contractor approved by the system manufacturer.  Make sure they produce a proper approved design and spec for their proposals and do not accept any "by others" clauses.

 

The rainwater outlet does not look great.  Also I am not sure if there is cavity tray and weep holes just above the upstands.  Failing that a coat of Storm Guard on the brickwork above.

 

Yes all roofers have said they would install a new outlet... There are weep holes on the outside of the wall (not onto terrace). If you look at the picture closely you can see them on the third course. I'm guessing that if replacing the copings with a DPC underneath, this should stop any water getting into the parapet wall cavity in the first place.

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  • 2 months later...

So is the weight of the slabs causing something to flex or separate and thus it leaks? 

 

Are the boards/roof under the slabs firm enough to take the weight of the slabs without flexing?

 

I've had some problems with both flat roofs and paving and had many conversations with roofers and patio layers.

 

I think they say that paving could always be kept two courses of bricks below your DPC as rain droplets can bounce that far and thus breach the DPC.  I'm assuming your upstands are in place of a DPC, so they should be higher especially around the bottom of door where there's a chance for water to get in. 

 

Is the paving sloping away from the house and towards the drains so that water doesn't pool against the house?

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It's difficult to say why removing a few slabs near the outlet stops the leak. I guess there could be any number of reasons but until the roof is fixed, that's how I've left it. I've had a real nightmare getting trades to fix this. I've found the guy I want to do the work, he has good reviews and came across well but unfortunately has been snowed under with overrunning work, made worse by some of his workforce having to self isolate etc.

Edited by steveoelliott
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I think the first thing i would do would be to remove all of the slabs, leaving the epdm exposed.

The second thing i would do would be to coat all of the brickwork inside the balcony area with a good couple of coats of Thompsons Water Seal.

The above Two things would give me a good idea of if the rain water is bouncing off the slabs, and making the brickwork above very wet.

I would have the coping stones removed, and have dpm run under them from the inner face to just more than halfway across the outside brick. I would have the copings re-laid but where they meet the wall, i would have lead saddles, rather than mastic.

Providing that solved it, next years i would have some of that fancy plastic decking put down on plastic bearers. Sorry, but i just don't like those slabs.

Hope you get it sorted. I would defo be doing some experimenting before i started having it ripped off. especially with winter coming along any day.

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17 hours ago, Big Jimbo said:

I think the first thing i would do would be to remove all of the slabs, leaving the epdm exposed.

The second thing i would do would be to coat all of the brickwork inside the balcony area with a good couple of coats of Thompsons Water Seal.

The above Two things would give me a good idea of if the rain water is bouncing off the slabs, and making the brickwork above very wet.

I would have the coping stones removed, and have dpm run under them from the inner face to just more than halfway across the outside brick. I would have the copings re-laid but where they meet the wall, i would have lead saddles, rather than mastic.

Providing that solved it, next years i would have some of that fancy plastic decking put down on plastic bearers. Sorry, but i just don't like those slabs.

Hope you get it sorted. I would defo be doing some experimenting before i started having it ripped off. especially with winter coming along any day.

 

Thanks Big Jimbo... Appreciate your feedback.

 

The coping stones where they meet all walls are joined with mortar rather than mastic. I agree with the lead saddles though and I think that's what my roofer is intending to do when they are replaced. I am looking to replace the stone coping stones with the more modern looking aluminum type.

 

Is the reason for the water seal application on the wall one of weatherproofing to prevent water penetrating the bricks?

 

I had considered running the epdm over the wall and under the coping stones but it seems some standards advise against that approach though. Also the EPDM material doesn't look very attractive and I certainly wouldn't want that on the taller parapet wall unless absolutely necessary.

 

 

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