Moisture in the attic...

I am a fairly new inspector. I have noticed in my last couple of inspections that there is a lot of moisture in the attics, so much so that the sheathing has black spots (looks like probably mold) and the moisture meter reads in the 15-18% range. In Michigan here we have had a fairly wet fall - just wondering what your opinions are… does there seem to be a lack of ventilation, or is this something that is fairly common at this time of year?

IDK about MI but if I saw that here I would be looking for the bathroom exhaust vents, proper insulation and ventilation, leaky ducts, or obvious openings to the conditioned area of the house.

That definitely appears to be mold- not “normal”. Like Juan said- its either a lack of roof ventilation, exhaist fans that are not connected to a vent cap, or a combination of the 2.

The strange thing is that all the exhaust fans seemed to be properly directed to the outside, and there were baffles at the soffits so the insulation didn’t seem to be blocking the ventilation… and the ‘mold’ signs were spread throughout the whole attic, not concentrated in a specific area.
Both houses that I noticed this in had ridge vents. I am kind of wondering if they are really as good as regular roof vents…

I don’t know what you mean by regular roof vents but a properly installed ridge vent and soffit vent is the best passive ventilation there is. Were the ducts in the attic? A chimney? Did the house have recessed lighting?

Seeing the blown-in insulation, did you look to see if the majority of the soffit vents were obstructed? Pretty common with the blown-in stuff. Even with baffles, they can be obstructed.

I dont consider this condition ‘normal’.

If everything looks OK, does anyone think that a missing vapour barrier on the attic floor could be a cause of this? But if vapour barrier was missing it would probably cause damage to the insulation before anything else. Just a thought.


A missing vapor barrier? Is that what you guys do in Canada?

Dont know what you mean when you say ‘do in Canada’? Are you asking if this is something we look for in a home inspection? Or are you trying to say that NO, this is not the cause of the problem we are discussing here?

Or maybe you just missed the ’ :slight_smile: ’ all together in your post.

I just meant that I’ve never heard of or seen a vapor barrier in the attic. The only barrier is usually the drywall and paint. I can imagine that in Canada it might be something used since it gets a lot colder up there. Are vapor barriers required or common up there?

Hi Juan,

I am not sure about ‘required’ but they are pretty common here. Perhaps more senior Canadian members can shed some light on the requirements for the VP in attic.


Yes, they are required here Gents.

What condition is the roofing in ?

They are absolutly required. It is part of your building envolope. Vapour barrier on the warm side of the attic insulation.

Gotcha. It’s not required here

Shingles were in OK condition. I am pretty sure that was not the cause.
Buyer hired a remediation guy to come in and look at it… $4-5000 to clean the mold out of the attic. I think they will also put a new ridge vent on to try to increase the circulation.