Mould Issue

[nelsonob1]

I added a carport on my barn last summer, basically wood framing, plywood deck, tyvak sheathing, tin roof. It's performed well with no leaks and is in a well vented, dry area of the field.

There is black mould or mildew spreading on the framing under the roof and the underside of the plywood. Don't have mould anywhere else on the building nor elsewhere on other outbuildings.

Hoping someone might understand what is going on and what I should no about it.

[sourdough doug]

You seem to have covered the bases......however....moisture = mold

[Desert Eagle]

One thing we found at Work, tin gets condensation on the bottom and you really need to have good ventilation to get air movement to help deal with it.

[Passthru]

What was used in between the tin roof and the roof sheeting? Tar paper? Poly? I’ve done Reno’s where home owners unknowingly used poly on the outside of the roof sheeting thinking it’s a great water barrier. It is, but, it will also trap moisture and condensation rotting out the roof sheeting. If that’s the case, you want tar paper. Tin roof also needs sleeper boards to space the tin roof from the roof sheeting. A tin roof doesn’t usually get roof sheeting anyways, just sleeper boards across the roof trusses

[Grizzly Adams]

Nelson BC. That's a dessert isn't it ? :confused:


Grizz

[58thecat]

What was used in between the tin roof and the roof sheeting? Tar paper? Poly? I’ve done Reno’s where home owners unknowingly used poly on the outside of the roof sheeting thinking it’s a great water barrier. It is, but, it will also trap moisture and condensation rotting out the roof sheeting. If that’s the case, you want tar paper. Tin roof also needs sleeper boards to space the tin roof from the roof sheeting. A tin roof doesn’t usually get roof sheeting anyways, just sleeper boards across the roof trusses

this...roof vents...good air circ....ave 74% humidity in this area....

[nelsonob1]

The layers are:

Framing - plywood- tyvak - tin.

The tin was not strapped. Screwed straight to plywood. But its a carport open on three sides.

[58thecat]

The layers are:

Framing - plywood- tyvak - tin.

The tin was not strapped. Screwed straight to plywood. But its a carport open on three sides.

moist air is hitting the tin and condensation is forming.... a redo is going to remedy this like passthru said...good luck.

[Austin]

Is air space needed between the tin and tyvex or do you need to remove the tyvex - trapping moisture

[Sundancefisher]

Does it make sense to rent a paint sprayer and spray the whole area with anti mould paint?

[nelsonob1]

Thanks guys, I guess I'm pulling it off this summer. You think the roofing contractor would have known this! Fortunately he strapped the barn.

[58thecat]

Does it make sense to rent a paint sprayer and spray the whole area with anti mould paint?

not fixing the issue just masking it......

[Arty]

Is air space needed between the tin and tyvex or do you need to remove the tyvex - trapping moisture

Actual Tyvek is designed as an outside air barrier to stop outside wind from pushing air through insulation and to stop air seeps through cracks and holes. It has a little bit of a moisture-extraction function, to slowly wick trapped moisture from its inside to its outside. But it's not supposed to be a moisture barrier like inside poly or a water barrier like outside tar paper would be.

So, for a building or room that is wide open to the outside like a carport, I don't see the point of having it on at all.

If anything, the roofing experts here might recommend tar paper under the tin at some point but Tyvek makes no sense. There is even some synthetic tar paper out there which is printed and might look like tyvek and be confused with it. But it's not real Tyvek, just a tar-paper(felt) that is easier to handle. https://www.gaf.ca/roofing/residential/products/roof_deck_protection/feltbuster