Mould and damp in attic space

jusmeig

Hey hey

Just noticed a significant amount of mould on the attic storage boards, and the back of the roof membrane is damp!

Recently did a home renovation.

House was wrapped in external insulation. Attic was insulated at floor level with 300mm of rockwool.

We had a mechanical heat recovery system installed. All ducts have been insulated with lagging.

I've no idea where so much warm air is coming from, as it seems the insulation is sufficient, and the MHRV properly insulated. I'll attach a few snaps.

The moisture is dripping down and some ceiling joists getting damp now.

The Continental Op

So whats the ventilation like in the attic space? Have you sealed everything up?

Sarn

We noticed a similar issue in our attic a few years ago when the weather was cold. House all recently renovated and insulated, ended up getting roof vents installed and the problem was solved. Our neighbours also noticed a similar issue after getting their place insulated.

Sonic the Shaghog

Also do a check on your bathrooms and see if the extractor fans are just vented to the attic. You wouldn't believe the amount of plumbers, electricians etc that did it and claimed it was the done thing even up to 4 years ago

jusmeig

https://www.boards.ie/discussion/comment/121583284#Comment_121583284

Thanks for reply. There are no traditional vents in the bathrooms, just vents from the mechanical heat recovery system. That is vented into roof vents so should be good. There is a lot of moisture up there!

The Continental Op

https://www.boards.ie/discussion/comment/121583318#Comment_121583318

So how is that moisture going to get out? Is there good ventilation up there?

jusmeig

https://www.boards.ie/discussion/comment/121583416#Comment_121583416

The vent in the wet rooms goes directly to the MHRV unit, which has a pipe leading to the outside. In terms of ventilation in the attic, it's a standard soffit with vents.

phelixoflaherty

Check the attic door seal

jusmeig

https://www.boards.ie/discussion/comment/121583605#Comment_121583605

Will do, at quick glance it looks fine.

Trying to resolve mould and damp is a tricky issue being honest. Ventilation is only a small part of the issue. Since you have had the attic insulated the temp has dropped dramitically in that space. So the warmer air below is now hitting colder surfaces up there which then results in condensation.

Roof vents might be advised. But they may or may not solve the problen.

jusmeig

I mean preventing as much warm/moist air getting into the attic space while also increasing the ventilation up there has to be the path forward. If I leave this as is I'm going to have serious mould. As it is, we are only in 5 months and there is significant mould growing 🙄

https://www.boards.ie/discussion/comment/121584053#Comment_121584053

Its going to be an issue with the 2.

Ventilation. Insulation.

Insualtion should keep the attic dry.

Ventialtion should let out moist air.

In my experience its never been thay easy.

gobo99

Check that the rockwool is not blocking the vents in the soffit. If it is, pull it back a little at the vents.

KungPao

It the damp localised or all over?

I had something similar over my en-suite, where the attic flooring was damp in winter. In the end it was steam rising up through some small gaps in the ceiling light. I've since taped the hole around the cable.

It may also be a soil pipe vent that terminates inside the attic, you have one? Hot water from showers can then rise up through this.

listermint

Soffit vents may be covered with your rock wool. Make 100 percent sure they are free and open.

Other than that. They may not be good enough to allow good airflow. You might need extra vent tile at the top to promote airflow soffit to vent pulling out the warm moist air.

Finally mhrv. The roof venting of these is probably the worst method tbh it's the reason I avoided this type of exhaust ventilation in mine. I opted to go through gable wall. The warm exhaust air from your mhrv can cling to to the inside of your flue stack and fall back down.

I would definitely have the exhaust of the mhrv checked both at the tile and down the exhaust pipe to unit.

10-10-20

Do you have foil-backed plasterboard on the ceiling or standard paper-faced?

jusmeig

https://www.boards.ie/discussion/comment/121584814#Comment_121584814

No, as far as I'm aware it's standard plaster board.

jusmeig

In relation to the soffit vents, our builder used pipes on all the gaps between joists that go down to the soffit. Because we have solar covering the south facing roof, adding vent tiles was not an option. So these plastic pipes were put in on both sides to endure insulation did not obstruct airflow.

https://www.boards.ie/discussion/comment/121584907#Comment_121584907

Plumbing vents?

10-10-20

https://www.boards.ie/discussion/comment/121584898#Comment_121584898

Then that's the probable path of the moisture as opposed to perforations in the foil/VCL if you had one fitted.

listermint

https://www.boards.ie/discussion/comment/121584907#Comment_121584907

Would need to understand the detailing here, it's unclear whether your new ewi or your rock wool, or both. Is impacting airflow. Was any of this a problem prior to the works?

tom23

https://www.boards.ie/discussion/2058330121/mould-and-damp-in-attic-space

Funny that... we got our attic insulated with the SEAI grant. And I've noticed a lot of condensation in the attic under the felt. The 'walkway' that was put was musty. I called the isolation company and they said thats to be expected and that they put in roof vents... still couldnt believe the amount of condensation...

listermint

https://www.boards.ie/discussion/comment/121585037#Comment_121585037

It's definitely not to be expected. Sole vents are useless unless there's supply . A 'flow' of air is required. Vent to vent. Soffit to vent is best. Or soffit to ridge even more superior.

tom23

so do I have a good reason to go back to them? they are reputable company and nice to deal with but am I been fobbed off?

listermint

https://www.boards.ie/discussion/comment/121585104#Comment_121585104

They should be checking the ventilation is working. Without adequate airflow then moisture cannot disappate.

You may need more vents you may need soffits checked.

tom23

I’ll drop them a mail tomorrow -

thanks for the heads up

jusmeig

https://www.boards.ie/discussion/comment/121585160#Comment_121585160

Did installing the additional vents remove the condensation problem or the company is just proposing that the vents are added?

jusmeig

It's not to be expected btw, by architect and builder have both said the attic should be bone dry and feel cold and breezy (like air moving not a freakin gale)

tom23

i took photos tonight - it doesn’t tell

the full picture there’s a lot of condensation

10-10-20

That's a crazy amount of condensation alright. I'd guess that the very cold periods where there is little wind isn't helping matters as it's not driving the moisture out of the attic.

Given that you have a MHRV system I'd wonder if you're not bleeding warm air into the attic at a loose junction?

jusmeig

https://www.boards.ie/discussion/comment/121589279#Comment_121589279

This is probably slightly worse than my problem. Had the MHRV guy out and he had a few practical tips. One of the steel boxes that connects the ducting was not covered in insulation, so would result in heat transfer, simple fix.

He noted quite a large roll of CAT cable not currently in use but run from the warm house to the attic. I had it lying in the area where it had collected quite a lot of condensation. It's copper after all. He advised me to bury it in the insulation.

My lift hatch seems to be the weak point tho. While it is insulated 36mm, r value of 1.1, the rest of the attic would be far higher. I've been advised to install a loft hatch cover to bring this area up to same r value as the rest of attic.

Finally architect said let's do above, which is all cheap enough, and if we done kill the condensation look to improve ventilation.

MHRV is basically an insulated box, and U are right I cannot rule out a damaged duct, but inspecting all of it would be troublesome. If above does not fix there are damp experts with flir cameras, that would be where we head next.