DIY Doctor

How necessary is a roof membrane?

Postby Curious7839 » Sun Apr 11, 2021 4:51 pm

The middle bedroom in my sloping roof house (built 1930) has had a continual problem over the years with a roof leak. This has always been attributed to the valley needing a bit of TLC. Once done, the leak would stop but eventually returns, usually about three years later.

With the return of the leak in the recent heavy rain, I’ve had a couple of roofers out again to take a look. One said that the only sure-fire way to get rid of the leak was to fit a membrane under the tiles. There is some water getting onto the rafters (obviously, because it’s leaking) but he also says he can see some “stage 1 rot” occurring. I’m partially sighted and I had difficulty seeing this for myself both in his photos and when I stuck my head up into the loft. The rafters are too far away from my reach to see if I could easily pull off some splinters of wood to check.

Obviously, fitting a membrane is a lot more expensive than repairing a valley. I’m prepared to pay this if it will. 100%, get rid of this wretched leak once and for all. My question is: is a membrane really the ultimate solution and can I be sure that the leak will be gone? Both the roofers I’ve seen offer 10 year guarantees on their work, so I can call them back if the problem returns in 2024. Both have said that I am not in need of a full valley replacement.

Thanks in advance for any and all advice offered.
Curious7839
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Postby stoneyboy » Mon Apr 12, 2021 9:28 pm

Hi curious7839
Unfortunately there is not a simple answer to your question. The fact that the problem re-occurs every 4 years or so indicates that there is an inherent defect or remedial work is not done correctly. Presumably your roof does not have under slater’s felt fitted. So yes it would be possible to strip back the valley and adjoining roof, fit a slaters felt of some form and replace the valley.
Will this solve the problem - there are too many variables to say yes.
Guarantees on roofing work are fairly ethereal - don’t place too much hope in them.
Regards S
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Postby Curious7839 » Fri Apr 16, 2021 7:36 pm

Thanks for your reply Stoneyboy and please accept my apologies for the delay in replying.

The roofer I saw the next day basically trashed what the previous fella had said (I thought he would) and I've gone for a repair with a 10-year guarantee. Putting in the membrane did seem a bit over the top. He seemed pretty thorough and also touched up a few other areas of the roof too (he thought water might be getting in through a skylight as well).

When he left he said "I've never been so certain in my life that a customer won't have any more problems". I said I'd let him know in 2024 if he was right. :)
Curious7839
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Postby stoneyboy » Tue Apr 20, 2021 9:34 pm

Hi curious7839
Valley gutters can be a regular problem if debris gets stuck part way down them, this can form a dam allowing water to penetrate the sides.
Hopefully you new roofer has sorted the issue.
Regards S
stoneyboy
Rank: Project Manager
Posts: 4463
Joined: Wed Dec 10, 2008 6:44 pm



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