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attic mold concerns after home inspection


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We are going through the home buying process. During the home inspection, the inspector pointed out mold in the attic. He didn't actually test it, just visually pointed it out.

We were concerned, and this is the feedback we received from the sellers: "Most attics have some staining. The staining on the backside of our attic was there when we bought this house 13 years ago and never got worse. We do not believe that it is a health issue, but they can test it if they want."

I'm going to reach out to our home inspector again this weekend. But I'm curious if anyone else has experienced this. I snapped one picture, it should be attached to this post. Thanks in advance.

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I see this quite often in homes. Can't tell from photo but it looks like the plywood sheathing may simply be darkened from moisture penetration, possible past roof leak. Quite common to see this at lower areas near eaves. It may be fungi/mold growth, if it is I would clean up remedy as necessary. Worse case scenario you might need to replace some damaged roof sheathing and patch the roof. If this is the only area it was found I would not let it be a show stopper.

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No need to test, it's mold that has most likely been caused by a poorly vented attic, improper venting, moisture migration from the living area and probably a little ice dam in the winter months.....

Is it a health hazard? It could be if you are allergic to mold. Does the home have a musty smell?

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It is a common problem in cold climates. Too much moisture entering the attic from the house, not due to roof leakage. Damp basements and crawl spaces and humidifiers are common causes, along with an easy way for air to enter the attic (pull-down stairway openings; pipe/chimney chases, etc.). If there is no ductwork in the attic it is my opinion that the exposure to mold is probably not significant, but some people are highly sensitive, so can't say it will not be a problem.

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You mean mould? This is Canadian attic mould. What you got there imight be a bit of stain from past mold growth.

Look for a source of moist air in that area. Sometimes moist air is coming in thru the soffits, maybe from the prevailing wind. I once saw stains in the soffit areas of an attic where the people had a steamy swimming pool behind the house. Soffit ventilation was bringing moisture in.

Usually the moisture is coming from warm indoor air rising from below.

Seal all gaps that are leaking warm indoor air into the attic. Pot lights are always leaky. The attic hatch should be insulated and sealed with weatherstrip. Bath fans leak. Warm air rises in the walls and bleeds into the attic at the top plate This house had all those things.

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It is a common problem in cold climates. Too much moisture entering the attic from the house, not due to roof leakage. Damp basements and crawl spaces and humidifiers are common causes, along with an easy way for air to enter the attic (pull-down stairway openings; pipe/chimney chases, etc.). If there is no ductwork in the attic it is my opinion that the exposure to mold is probably not significant, but some people are highly sensitive, so can't say it will not be a problem.

I'm with Mark. I doubt its a roof leak. Maybe a bathroom exhaust fan under all that crappy batt insulation? Recessed lights out of the pic? Most likely an air seal problem.

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Your home inspector perhaps should have better addressed your concerns.

Addressing your concerns is his primary job description.

As mjr6550 and others opined, the issue is common and is likely a result of multiple factors that combine to cause the attic air to become saturated. Saturation happens when air temperatures and dew points become the same.

A crack inspector onsite is your best bet to get answers.

Marc

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Thank you for the feedback. I do believe my inspector addressed my concerns at the time. He pointed out what he considered mold, and told me that it was due to poorly installed baffles (which he also pointed out).

My realtor informed the seller's realtor of the mold, and last night I received their response. I won't be speaking to the inspector again for a day or two, so I figured I'd post it here to see if it made any sense at all.

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I once saw stains in the soffit areas of an attic where the people had a steamy swimming pool behind the house. Soffit ventilation was bringing moisture in.

John, any chance that was the north side of the roof? Moisture in the attic in the middle of the summer from the swimming pool?
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I once saw stains in the soffit areas of an attic where the people had a steamy swimming pool behind the house. Soffit ventilation was bringing moisture in.

John, any chance that was the north side of the roof? Moisture in the attic in the middle of the summer from the swimming pool?

Yes, North side. I don't know when the moisture was worst. Only was there for 3 hrs, eh? [:)]

Maybe in the fall when they were heating the pool? The attic had mould and stains only where the pool was adjacent. Still just a guess on my part.

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I do believe my inspector addressed my concerns at the time. He pointed out what he considered mold, and told me that it was due to poorly installed baffles (which he also pointed out).

The baffles may or may not be the problem - there can be several potential causes. Even a well ventilated attic can have dampness issues due to some other problem in the building.

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told me that it was due to poorly installed baffles

Not sure I agree. As others are pointing out, humid air in the attic is the cause and controlling the source is the solution. It is likely mostly from the interior, and the fix is to "air seal" the attic floor. This would normally be done by an insulation, weatherization, or home performance contractor. If it were me I would remove all the fiberglass so I could see the entire floor, air-seal the whole thing while running a blower door, then replace the insulation with blown-in material. Very easy job for someone who knows the drill.

You should also look at the exterior. Is there a window below that stained area?

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  • 2 weeks later...

I sometimes see this on a north side only. I am in a dry climate and from what I am seeing is this happens during certain conditions where there exterior humidity shoots up and the roof is still cold causing condensation. Typically this is an early spring late winter event. The moisture is actually coming from the exterior of the home.

Not knowing that this case here, but thought I would throw this out for food for thought if you are in an area like Eastern Washington.

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I sometimes see this on a north side only. I am in a dry climate and from what I am seeing is this happens during certain conditions where there exterior humidity shoots up and the roof is still cold causing condensation. Typically this is an early spring late winter event. The moisture is actually coming from the exterior of the home.

Not knowing that this case here, but thought I would throw this out for food for thought if you are in an area like Eastern Washington.

I agree. Very common here as well.

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