New Membrane Leaking Multiple Places Valley

BathDIY · 20 Nov 2020

Installed Cromar Vent 3 Light membrane in the roof valley area and noticed leaks along plywood installed to support the fibreglass valley in multiple places.

More membrane has been nailed up on top just to prevent water ingress.

The leak seems to have stopped now despite more rain indicating that it is something about the new installation.

oldbutnotdead · 20 Nov 2020

You sure the membrane is leaking rather than it being condensation (from warm air in the loft hitting very cold membrane)- I've had that with that exact same membrane type.
And leaks while just the membrane is in place aren't a definite indicator of problems for the future- see what happens once you get the tiles back in place.

BathDIY · 21 Nov 2020

I thought as the membrane was breathable condensation couldn't be causing this. I did notice it in the morning then added more on top which stopped the issue (despite heavyish downpour). I imagined that condensation would gather uniformly not in patches (appreciate no images of this it dried so fast after I added the additional membrane).

I am relieved that you have had similar issues.

datarebal · 21 Nov 2020

Some of the underlay is creased and taught, battens poorly joined . Water will seep through nail holes if not done properly.
Some of those short bits of batten are not ideal.
The screwed little bit is poor.

You can get condensation even if it's a breathable membrane. Usually while there's drying out going on.
Worth remembering too , most breather underlays are water resistant ..not water proof.
Heavy rain and direct strong winds can make it pour in

Owen74 · 12 Nov 2023

I have that same type of valley on roof and get terrible problems with condensation on the underside of it, despite doing all I can for insulation and ventilation.

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New Membrane Leaking Multiple Places Valley

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