Roof ventilation help condensation and mould

[Looba45]

Hi everyone hope you're all well and enjoying the warm spell. 

 

In need of some help with my roof which I did myself (novice roofer/builder) in the summer. Looking for advice and not criticism please! I have a loft bedroom and it has recently been plagued with bad condensation and mould, and I believe the issue is that there isn't enough air flow between the insulation and felt. I was wondering if installing vents in certain locations as on the drawing I've done will help or just make things worse. It's a fiber slate roof with breathable felt, eve vents and dry ridge with the felt cut at the ridge.

 

Holding my hands up, this was a big lesson, I opted for more warmth than airflow and I'm paying for it now. Just wanted to see if what I suggested is an option to avoid having to get the scaffold back up and the insulation board swapped.

 

Thanks 

[Mr Punter]

Yes, ventilation will help.  Also you need to prevent warm moist air getting into the structure.  What type of insulation?  Is it all boarded and finished?  Where is the mould?

[Looba45]

I've brought an electric dehumidifier to try and stop the moisture and it is 50mm recticel insulation board with expanding foam to stop heat gaps. The mould is gathering on the breathable felt and picture frames stored in the eve cupboards there is insulation board between all the roof rafters and floor joists in the the eve cupboards. 

[Looba45]

The loft room is all plasters and finished with 2 velux and dormer. 

 

[Mike]

13 minutes ago, Looba45 said:

I believe the issue is that there isn't enough air flow between the insulation and felt. .....It's a fiber slate roof with breathable felt

If it's a breathable membrane installed in accordance with the manufacturer's recommendations / the BBA certificate, and the conversion was done to Building Regulations standards, then the probability of that being the source of the problem is low. More likely it's a problem generated within the house.

 

Condensation is caused when warm humid air cools down, which suggests that you need to improve ventilation in the room / house, remove or reduce the sources of humidity, improve the heating in the room, or all of these. As the problem is only in this room, maybe that's because it's not much used and therefore may has a shut door and maybe isn't heated often / much? At least I'd guess that the eves cupboards are the least heated / worst ventilated part of the room.

[Roger440]

Im unclear where the condensation/mould is?

 

In the room or outside of it?

 

 

[Looba45]

Yes the membrane was installed correctly and the loft room was there when moved In. it's just the roof that is new. It is only used for sleeping in and doesn't get much heat. I have been wondering if re plastering with a damp proofing behind the plaster would help? As a solution in the future. The eves cupboard is in the cold part of the roof where the air flow is and shower /bathroom underneath with an old extractor fan. 

[Looba45]

The condensation mould is not in the room it's on the felt/rafters and eve storage cupboard that is separate to the bedroom. 

[Looba45]

Iknow the diagram of the roof vents I've drawn is far from detailed but wondering if where I'm planning on placing the vents will help with the intake/ outtake and airflow, never had a problem with condensation before the new roof. And just wanting a cheep fix while Christmas time is always hard financially.  

[Mike]

1 hour ago, Looba45 said:

It is only used for sleeping in and doesn't get much heat. The eves cupboard is in the cold part of the roof where the air flow is and shower /bathroom underneath with an old extractor fan.

That ticks off everything I mentioned above. So most likely a major part of the solution is to replace the extractor fan, boost the room temperature, and leave the eves cupboard doors open. And apply some mould killer.

 

1 hour ago, Looba45 said:

I have been wondering if re plastering with a damp proofing behind the plaster would help?

It seems unlikely that the damp is coming through the roof (if that's what you're thinking the damp proofing would help), so probably not. But maybe I've misunderstood.

 

1 hour ago, Looba45 said:

wondering if where I'm planning on placing the vents will help with the intake/ outtake and airflow

As you're sure it's all built OK as above, I don't think that's likely to help.

[Redbeard]

Is there a leak in the extractor fan duct, or around its exit through the bathroom ceiling (i.e. are you feeding water vapour into the eaves void?

In terms of 'quality' of ventilation I much prefer eaves ventilation (preferably about 25mm) across the whole width of the roof on both sides, so that you have excellent cross ventilation. In most of the situations I come across with a roof moisture problem where a few tile vents have been used, the problem continues, suggesting that whatever number of tile vents you think of putting in, it's often not enough. Add to that the fact that they tend to start say 900mm above the gutter, and that leaves the water vapour 'un-purged' from the bottom of the triangle.

 

[Looba45]

Sorry by damp proofing I meant vapour barrier to keep moisture in. And will definitely try what you said and see how it goes, thanks.

 

[Looba45]

And no leak just an old extractor fan that sounds quite haggard and is coming out the wall so the steam could be coming back in through the existing eve vent. I installed the eve vent when I did the roof it's just that there's not a 50mm air gap That can take the air up to the ridge line. was planning on installing 8 altogether. 2 either side just where the air gap gets tight 20mm so could be sucked in the eve and put the vent and 4 at the top 2 low down just above the 20mm gap and 2 higher up in the hopes air will flow through one side and out the other.