Attic Rafter Insulation (attic is damp).

Gumbyman2000

Hi! I'd love to get any opinions on my plans here.

Problem: My attic is damp & every Winter stuff gets a coating of mould. The attic is floored and insulated underneath (so is outside the envelope of the house, technically). However, warm & hot air is rising up and into the space. It hits the cold surfaces in the attic and condenses. The roof felt for example weeps.

Planned solution: bring the attic within the envelope, or at least reduce the temperature differential between the attic and the rest of the house, by insulating between the rafters (rockwool, not pumped, hoping to do it myself - stuffing it between the rafters and securing with battens, any tips here most welcome!).

Note: I have tried to reduce the humidity in the house, but can't nail it that way. Short of running dehumidifiers 24/7 in the house & in the attic, which is not sustainable.

Does this plan make sense? Any flaws or suggested improvements?

Thanks!

Steve.

Dave 101

Is the roof felt Breathable? Sound like it’s not, might need to look at getting roof vents installed

denismc

You need to improve the ventilation in the attic.

I would think roof vents would be your solution, they seem to be standard now on any insulation upgrades.

listermint

You're eves probably have no Ventilation in them. You need a mix of that and roof tile vents. That the only real solution.

Gumbyman2000

Hey! Thanks everyone. I appreciate the advice and had a good think about it. I'm worried that roof vents might make it worse by further cooling the attic space, thus increasing the temperature differential between the attic and the warm (humid) air rising into it from the house, without a sufficient airflow to get rid of the humid air out of the attic. That humid air will condense even more on the (now) colder objects in the attic. That's why I was thinking of going the other way and including the attic in the envelope. Whadday reckon? Is it a valid concern?

Alkers

Make sure your extractor fans are not leaking into the attic space.

What ventilation is in the attic as is?

Gumbyman2000

Thanks - looks like they pump to external vents.

Very little ventilation in the attic, I haven't been able to find any under the eaves. I can see a tiny bit of daylight at the top of both apexes (if that's the right word - the triangle of concrete wall at both ends).

bfclancy2

https://www.boards.ie/discussion/comment/121277543#Comment_121277543

ventilate the attic, ensure attic floor is adequately insulated so heat is not rising from house below, that will ensure no issues, including attic in the envelope is the wrong approach in my opinion, no need for it, address other two issues (these are easily sorted) and you will have no problems

antoinolachtnai

https://www.boards.ie/discussion/comment/121277543#Comment_121277543

You could do what you describe, but it is a very big project. It is not as simple as putting some insulation between the rafters. You would need specialized advice for this.

It should be much more simple to ventilate the attic. If it is properly ventilated, the humid air will ventilate out of the attic.

It does sound like there could be some sort of significant leak of humid air from the upper storey rooms into the attic, in addition to the lack of ventilation.

Penn

https://www.boards.ie/discussion/comment/121277710#Comment_121277710

I have to agree.

Warm air can carry more moisture in it than cool air, and stale/stagnant air (through lack of ventilation) will also contain more moisture. Depending on how the flooring of the attic was done, it's likely that it's affected the insulation layer at ceiling level, as otherwise you should not have warm air getting into your attic from the rooms below.

You're better off improving the existing insulation envelope and airtightness at ceiling level than trying to create a new one at rafter level, particularly as rockwool between the rafters will likely not be thick enough to form an insulating layer to current standards and you'll then have two insulating envelopes which don't address the issue. Improving the insulation at ceiling level will prevent heat from within the house entering the attic, and ventilating the cold attic space will reduce the moisture content in the roof void and thereby reduce condensation/mould.

listermint

Exactly as clancy and Penn have said above.

Majority of attic spaces in Ireland are cold zones. With fibre wool insulation and ventilation in them.

You've no Ventilation. You need it. It's meant to be a cold space it's per design it needs airflow and a decent amount.

Unless your going to shell out of a conversion don't undertake anything like brining it into your envelope. You won't have the expertise and will cause other problems.

Shoog

I agree with the general advise, improve the ventilation.

Your house sounds a bit like my old 1950s house with no eves ventilation and no possibility of adding any. Higher up cross ventilation might be enough to draw the moist air out. We get condensation on the north side of the roof and I cannot think of how to address it.

If you were to try to improve insulation you could try what we have done in some rooms, drop the ceiling by about 30cm, add 20cm of insulation and finish off by adding a vapour barrier on the bottom before your finish layer. It has transformed our houses comfort level and will have reduced moisture ingress to the attic.

Gumbyman2000

Hey! Spot on, thanks a million for all the advice here, the verdict appears to be unanimous which is always very useful! I'll do as advised - stick in some crossed roof vents (not sure I can do anything with the eaves, but I will check). Not sure I have the height to drop 20cm of internal insulation, but I'll go step by step and see how the vents go for starters. No obvious humidity leaks but will rethink that side of things too and see if any sneaky culprit.

Again, thanks everyone - I really appreciate the advice, wonderful people.

Cheers,

Steve.