Cedar Shingle Roof Moisture ingress or mould?

[BadetBadarkos]

The issue I am having with mould. I would appreciate folks' thoughts and help.

For context, we are based in the UK, and our construction system consists of; cedar shingles, cedar breather, felt underlayment, plywood, actis multi foil 90mm with an integrated vapor barrier followed by a plywood lining internal lining.

Essentially, we're having some mould marks internally now. I am unsure whether this is caused by mould due to humidity levels being as high as 80% in the cabin continually for the past 2-3 months or if it is due to poorly fitted roof shingles causing water to run in? Were going to install a de-humidifier etc as a starting point.

The issue is a roofer I spoke with today said we would need to rip the whole thing off and start again. Our shingle gauge is 150mm, but the roofer said this would need to be 125mm, which he believes is causing the issue. The roof has a pitch of 45° and 90°. Of course, we want to avoid this and would appreciate your thoughts.

I have attached some photos, including the interior, that show the mould.

 

[freddiemercurystwin]

When you say 'felt underlay' do you literally mean actual felt or do you mean it's a breathable membrane? A sketch showing the exact roof makeup would help. Why is the humidity so high? Do you have any background ventilation eg trickle vents in the windows etc? How often do you open the windows? What is the heat source? How often is it running? What is the purpose of the room, how often is it occupied? Interesting build!

 

[BadetBadarkos]

When you say 'felt underlay' do you literally mean actual felt or do you mean it's a breathable membrane? A sketch showing the exact roof makeup would help. Why is the humidity so high? Do you have any background ventilation eg trickle vents in the windows etc? How often do you open the windows? What is the heat source? How often is it running? What is the purpose of the room, how often is it occupied? Interesting build!

Hey, thanks for the response. So, I have attached an image of the detail and the wall build-up. To answer why the humidity is so high. I am not sure to be honest. It's not being used at the moment, we do have trickle vents in the windows however, i have just opened them today only. We do not open the windows often. The heat source is biofuel, which creates more humid air, however we will install a dehumidifier shortly.

My concern is it is moisture ingress, I am worried the 150mm gauge is not enough, has to be 125mm, requiring us to remove the whole thing.

 

[BadetBadarkos]

To answer the rest of your questions, its not used often at all, its intended final use is as a holiday let but its still a build in progress.

 

[freddiemercurystwin]

So are you saying the felt on the walls is the impervious traditional type?

 

[BadetBadarkos]

The felt we used tyvek uv facade

So are you saying the felt on the walls is the impervious traditional type?

 

[BadetBadarkos]

Per this detail

 

[freddiemercurystwin]

Are there no counter-battens between the plywood and the shingles?

 

[BadetBadarkos]

There are not no, its a US construction method but it is used in wet areas the 'cedar breather' acts as the counter battens.

 

[freddiemercurystwin]

Hmm, well in the UK you'd normally adhere to UK construction methods, see how you go with the ventilation, that won't have helped. What was the exact insulation?

 

[freddiemercurystwin]

Going back to your first pics, are those massive glazed bit just perspex?

 

[BadetBadarkos]

Yea, because of the curved structure, the Cedar Breather US product made sense. Many people recommend it out there and as shingles are more of a US construction system, it made sense at the time. Insulation is: Actis Multifoil 90mm.

 

[BadetBadarkos]

Going back to your first pics, are those massive glazed bit just perspex?

That is a 35mm multiwall polycarbonate, for context, it has similar u-values to double glazed windows.

 

[BadetBadarkos]

I have just seen this chat from some years back that you were involved in, they were looking at using the Benjamin Obdyke product as well: https://www.diynot.com/diy/threads/ventilating-underlay-for-cedar-shingles.507566/

 

[freddiemercurystwin]

That is a 35mm multiwall polycarbonate, for context, it has similar u-values to double glazed windows.

OK but how are the windows sealed? What are the others made of - they just look like thin perspex screwed to the frame over a seal, any hybrid windows like that will be prone to water and air leakage etc, suspect that will be the cause of your high humidity.