Damp in loft despite breathable membrane (Ed.)

[Owen74]

And yet it passed all the building inspections... really worrying.
I thought I could work around this by sticking superfoil insulation on the underside.
Now I'm wondering if the whole valley needs ripping up and redoing with felt underneath.

 

[Owen74]

It's just literally bare exposed plastic on both sides. That's all they did on the build. Isn't this a building regs thing?

 

[berty3000]

My house was re-roofed using Cromar Vent3 Pro and I've come to the conclusion that venting is required. I intend to use lap vents and soffit vents to introduce more air movement.

I spoke to somebody at Cromar over the phone and they told me that this membrane doesn't let moisture or air pass through it. I was surprised by this and asked why it was called breathable in that case. They said it results in a breathable roof when used in conjunction with venting as moisture is less likely to condense on to it than older type felts.

However, having looked again at their technical information, it does specifically say that it is vapour permeable.

I'm confused.

 

[Owen74]

My house was re-roofed using Cromar Vent3 Pro and I've come to the conclusion that venting is required. I intend to use lap vents and soffit vents to introduce more air movement.

I spoke to somebody at Cromar over the phone and they told me that this membrane doesn't let moisture or air pass through it. I was surprised by this and asked why it was called breathable in that case. They said it results in a breathable roof when used in conjunction with venting as moisture is less likely to condense on to it than older type felts.

However, having looked again at their technical information, it does specifically say that it is vapour permeable.

I'm confused.

Me too, my question would be is there any reason to NOT add vents when a so called breathable membrane is used. I'm going to add some lap vents to mine this week and see what happens.

 

[Owen74]

I'll see your "Oh dear" and raise you a "WTF?"

I hardly dare ask but how big a job might that be for a roofer to take up the valley and replace it with felt/membrane under it. Presumably it would entail lifting a load of tiles and replacing the battons either side too.
Would this be an essential thing to do, in order to protect the woodwork?

 

[berty3000]

Me too, my question would be is there any reason to NOT add vents when a so called breathable membrane is used. I'm going to add some lap vents to mine this week and see what happens.

Having discussed this with several roofers, posted threads on these forums, and read up a lot online - the overwhelming consensus seems to be that ventilation is a good thing. At worst, it won't do any harm.

Worth bearing in mind that new builds will use breathable membranes and are expected to have vents, at eaves and ridge levels. It will enhance any breathability the membrane has.

Perhaps less ventilation will be needed than if the membrane were not breathable. I am planning to put 70mm round soffit vents in at roughly 1m centres. So that will be 30 around my bungalow. I will then add these lap vents, maybe ten of them, higher up in the attic. So then the two will work together - fresh air drawn in from the soffits and exhausted higher up where the air pressure is lower, taking moisture with it.

It will make the attic colder (more like the outside), but also drier and fresher. The home below will be protected by all the insulation sitting above it. I intend to ensure that pipes in my attic are adequately covered in insulation to reduce the odds of freezing once this cooler air is being vented in over the winter.

 

[cdbe]

I used proctor roof shield, very expensive, when you hold it up you can see tiny pin holes in it - hopefully it lets warm moist air out but not water in.

 

[berty3000]

I think the membrane in my attic has been installed a bit too tight for me to be able to install these lap vents. Annoying. So there goes the nice easy and cheap DIY option. Unless I can use some smaller objects to open up gaps... pieces of 10mm plastic pipe maybe? Otherwise, looks like tile vents will need to be installed and felt beneath them cut.

 

[^woody^]

I hardly dare ask but how big a job might that be for a roofer to take up the valley and replace it with felt/membrane under it. Presumably it would entail lifting a load of tiles and replacing the battons either side too.
Would this be an essential thing to do, in order to protect the woodwork?

Not so much a big job, but an awkward job - and therefore roofers may not want it or price it high.

Left, it may well be OK for years, but it's a massive risk as you won't have the second line of defence for any leaks at the valley.

 

[Owen74]

Not so much a big job, but an awkward job - and therefore roofers may not want it or price it high.

Left, it may well be OK for years, but it's a massive risk as you won't have the second line of defence for any leaks at the valley.

Thanks, I am more worried about the immediate risks from condensation seeping into woodwork, rather than future leaks in the valley. Although by the sound of it this job of replacement is best done before that happens.

 

[^woody^]

If the valley underlay was there, you would not see the condensation. It may still occur but not within the roof space.

 

[Owen74]

If the valley underlay was there, you would not see the condensation. It may still occur but not within the roof space.

Presumably it would also protect the wood beams from the condensation.

 

[noseall]

Presumably it would also protect the wood beams from the condensation.

Correct.

 

[JohnD]

CONDENSATION IN LOFT (ANSWERS)

This seems to be the time of year for condensation in lofts, so instead of replying to lots of queries I though I would write this "one-size-fits-all" post. Please also see //www.diynot.com/wiki/Building%3ACondensation-in-Houses Condensation in lofts occurs when the amount of water...

www.diynot.com

 

[Owen74]

Correct.

OK. Given my current situation - the plastic roof valley is exposed, I can't un-expose it, but I can cover/insulate the underside of the roof valley to stop the warmer air condensing on it.

(I've had some luck wiht this on one section, using SuperFoil bubble wrap).

Plus I need the usual measures for ventilation and insulation in the loft space, of course.

I can't do anything about possible future leaks in the plastic which may happen, I can only live with the awful risk - and hope the plastic doesn't crack or leak - maybe replace in a couple of years just in case.

Meanwhile I'm trying to get a roofer to look at it for an expert opinion / risk assessment.

Does this sound like a reasonably sound plan?