Flat roof question.

Recent rain has shown my flat roof is leaking. It's part of a conversion built about 30 years ago. Very nicely built - the correct lie etc and marine ply decking, and lead flashing. Think it is three layer. Size
approx 5x5 metres.
Any of the modern alternatives better? Membrane or fibreglass? And a rough idea of relative costs would be nice too.
Access is easy, but it's never walked on etc except for any maintenance.
--
*I tried to catch some fog, but I mist.*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Sun, 26 Jul 2020 13:35:58 +0100, Dave Plowman (News) wrote:

I find it mildly curious that in the 21st century, no one has seen fit to come up with something that can be poured, finds the crack and seals it ...
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On Sun, 26 Jul 2020 13:42:50 -0000 (UTC), Jethro_uk

I have done just that with Isoflex liquid rubber. Leaked at the junction between my and my neighbour's garage roofs, bitumen felted. Must have been quite a big crack as it took quite a lot, and at one point appeared dribbling down the inside of the garage wall. Sealed the leak though. https://tinyurl.com/y2fgfmzo
--

Chris

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It's already had that treatment. But same as paint, doesn't last forever.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 26/07/2020 16:32, Dave Plowman (News) wrote:

Isoflex, when used with its special primer should add about 8 years to the life, provided it has no ponding or other problems.
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On Sun, 26 Jul 2020 14:07:41 +0100, Fredxx wrote:

Had ours fibre glassed about 10 years ago. New OSB boards, the old torch-on felt had failed and knackered those boards. Took the oportunity to fit 100 mm of celotext between the roof joists. The fibre glass is still waterproof or at least if it is leaking it's not getting to anywhere visible inside. But then there is a poly sheet on the warm side of the insulation and up and over the joists...
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Big snag is actually knowing how long these 'new' methods do last. Plenty claims, though. The decking is marine ply, so hoping it will still be just fine. The chippie who did the work was very good indeed.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Sounds like the story of the salesman who turned up at Steinway pianos saying "We've got this wonderful new material for piano hammers instead of that old fashioned felt." Steinway said they try it out. "Ah, when should I come back?" "In about 100 years."
--
from KT24 in Surrey, England
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On 26/07/2020 19:18, charles wrote:

Sometime in the 1970s I was involved in a submarine cable project. Featuring Germanium transistors "Silicon hasn't been around long enough to know they will last"
Asked my oncologist "what is the 15 years outlook for this chemotherapy?" "Dunno: it's only been around just over a decade"
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On Sun, 26 Jul 2020 18:20:35 +0100, Dave Plowman (News) wrote:

True enough, though glassfibre has been about for quite a number of decades in other things like boats.
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On 26/07/2020 18:20, Dave Plowman (News) wrote:

Marine ply won't disintegrate if it gets wet - it'll just dry again.
Unless it keeps getting wet, when it will rot just like any other wood.
Andy
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On Thursday, 30 July 2020 21:58:01 UTC+1, Vir Campestris wrote:

Marine ply is one of those things much talked about but never seen in diy or pro house maintenance. If someone says marine ply, it's something else.
NT
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Most timber yards round here sell it. Or rather what they call marine ply. At about 5 times the price of general purpose stuff.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 31/07/2020 14:22:14, Dave Plowman (News) wrote:

If you want to go to the extreme make sure the marine ply it is of the WBF type. A further extreme is to get Buffalo board. I've used it on a shed roof without felt. My experience is it lasts 25 years in the open air environment and is still serviceable and waterproof.
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I'd say you'd have to ask them. ;-)
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*I couldn't repair your brakes, so I made your horn louder *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Sun, 26 Jul 2020 13:35:58 +0100, "Dave Plowman (News)"

Here you go, Dave. Don't say I never do anything for you:
https://polyroof.co.uk/
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On 26/07/2020 15:22, Chris Hogg wrote:

Joints in flat roofs are almost guaranteed to fail, especially if both were originally built-up 3 -layer felt and one half has been replaced with 2-layer torch-on felt. The heat of the sun, and the dryness, especially the weather we have had this year will soon make the joint fail.
IS the decking chipboard, plywood or OSB ? The first will not like ingress of water.
If you are going to treat flat areas their special primer is well worth using first.
I did my garage roof with an EPDM kit, but that involved redecking with OSB3 first. 5.5 mtres by 2.8 metres. It was just on the limit of my ability to get it up the ladder. A 5x5 sheet of epdm will need 2 people.
Flat roofs need replacing at least every 20-25 years. Some really bad bodge jobs, like the garage roof of my first house was done in 2-layer felt in 1976, before the days of fibreglass reinforced felt and every house had a leaking garage roof within 10 years.
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On 26/07/2020 13:35, Dave Plowman (News) wrote:

Glassfibe will be quite a bit more expensive than EPDM. Probably best to find a roofer who can provide quotes.
I don't think any special tools are needed to install EPDM, so it may be suitable for DIY, though you may need several people to handle the weight. It took 1 day to reroof a double garage with EPDM including changing some boarding and maybe a joinst.
--
Michael Chare

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On 26/07/2020 13:35, Dave Plowman (News) wrote:

How about old fashioned lead ?
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Doesn't help indoor FM radio reception.
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from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
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