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Attic Mold/Mildew


Rick Bunzel
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Anyone know where I can find any articles about attic mold? I would like something that I can pass on to sellers/ buyers etc. I probably find symptoms in 5% of the homes I inspect.

I would also like to hear how inspectors refer this out. Sorry guys but I don't like referring it to Mold Mitigators or qualified professional. The mold guys are like grave robbers and trying to describe what a qualified professional is to my client or worse yet the sellers realtor is a royal pain.

//Rick

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Rick,

You can always send them to the CDC website. http://www.cdc.gov/mold/

My main concern when I see "mold", it to try and pin down what caused it. Then I can properly explain to my client what needs to be done to remedy the situation. In attics it always one of 2 things. Blocked vents/not enough venting, or an active leak. I also run into the disconnected bathroom fan duct that might have caused some mold.

Show your clients the pics, or if the hatch is easily accessible, let them look. Explain what you see and what the likely cause is.

Hope this helps.

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Rob,

I run into a few recently that aren't so simple. For example last weeks attic mold was as follows:

New house built in 2008 but never occupied. Attic had 15" of insulation (R-38) , eave baffles, full ridge vent and no visible openings between living space and attic. Roof deck was osb and visibly dark from the mold/mildew. The mold shadow appeared to be pretty even on the north side of the attic so not apparent source of the moisture could be located. Heat was radiant floor and I was told was kept between 55-60 while house was on the market. My client's really like the house but if the issue grew this fast in 2 years they will probably walk unless the root cause can be identified and resolved.

Quite frankly the CDC is pretty basic and really doesn't address these type of issues.

//Rick

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15" of insulation, by itself, doesn't mean anything. If it was low density white fluff, it convects air (and moisture in the air) right up into the attic.

Ventilation, by itself, doesn't mean everything is OK. Ventilation can increase stack effect in a home, causing moisture migration to the attic.

There's got to be a moisture source; otherwise the mold won't grow. You could have any number of strange little micro climates that are causing moisture to condense, travel, or otherwise find it's way to the underside of the sheathing.

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Hi Rick,

I wouldn't bother going to the CDC site, they know germs but they don't understand squat about building science. The EPA mold site is a little better and the Association of Walls and Ceilings used to have a pretty good free book on their website for download. Check out the forum "free downloads" or some such. I think I put a link to it in there.

Were there gable end vents in addition to the ridge vents? I keep finding those; the damned builders here are taking a belt-and-suspenders approach and seem to think that having gable end vents will help ventilation when it usually inhibits how well the ridge vent pulls air from the eave vents.

I'd tell 'em to get the underside of the roof nuked with BoraCare® a go on with their lives. Once the deck is saturated with that stuff it's going to be Chernobyl for fungi.

ONE TEAM - ONE FIGHT!!!

Mike

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Rick,

I've become convinced that, in our climate, in some (not all) attics, "proper" ventilation *causes* condensation and mold growth.

Short version: In some houses, during certain times of day, the air that's drawn in through the soffit vents is warmer than the attic sheathing and causes condensation on it.

- Jim Katen, Oregon

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Short version: In some houses, during certain times of day, the air that's drawn in through the soffit vents is warmer than the attic sheathing and causes condensation on it.

I just saw Lstiburek and he said the same thing. The sun beats down on the wall and the warm air rises into the soffit vent, melts the snow on the roof deck and causes an ice dam on the exterior and condensation on the interior.

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Interesting. One question: If we limit our consideration to those dwellings on which there is no snow on the roof, would that eliminate the incidence of having a roof deck cooler than the incoming soffit air?

Marc

No. All it would take would be a tree that provided shade on the roof while allowing sun to hit the wall.

Or, in my climate, a roof that was cooled by constantly falling rain while the wall, protected by wide overhangs and warmed by heat loss from the house, would provide a film of warm, humid air rising up into the soffit vents.

I've heard from others that houses in the southern states don't have attic condensation problems. Is that your experience?

- Jim Katen, Oregon

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I've heard from others that houses in the southern states don't have attic condensation problems. Is that your experience?

- Jim Katen, Oregon

Absolutely. I've seen but one case of attic condensation issues in 7 years here, involving an air handler and high humidity. Makes me come up short when I'm on a forum with membership mostly from the northern states.

I do enjoy the 'exercise' though, and the opportunity to expand my understanding of concepts. I know the principles of psychrometry well from my AC background, but I have to labor to apply them in ways not seen down south.

Marc

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The problem is caused by a fundamental flaw in our building science, compounded by a removal of qualifications to design buildings.

First, the vast majority of new homes are designed by the builder, the material provider, or a home designer these days, no training required. They are flawed while still in plans, so it's really surprising that more of them aren't seriously flawed as buildings.

Second, we have this magic bullet called attic ventilation, a one size fits all system that is left to no less than 3 trades to properly install. It's a wonder any of it works at all, so why are we surprised when we find one that has failed?

Ventilation needs to be designed for the building, and just like any other system, installed by a single skilled trade, but until there are more stringent requirements for the people designing buildings that is just a pipe dream.

Tom

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The problem is caused by a fundamental flaw in our building science, compounded by a removal of qualifications to design buildings.

First, the vast majority of new homes are designed by the builder, the material provider, or a home designer these days, no training required. They are flawed while still in plans, so it's really surprising that more of them aren't seriously flawed as buildings.

Second, we have this magic bullet called attic ventilation, a one size fits all system that is left to no less than 3 trades to properly install. It's a wonder any of it works at all, so why are we surprised when we find one that has failed?

Ventilation needs to be designed for the building, and just like any other system, installed by a single skilled trade, but until there are more stringent requirements for the people designing buildings that is just a pipe dream.

Tom

Lots of truth there.

William B. Rose writes about this a bit in his book. Our current mess of building code mis-perceptions are based on incorrect conclusions about building design and materials that go back to the 30's, when insulation was first being installed in buildings.

The introduction of new insulating materials has compounded some of the original mis-perceptions, as the same untrained folks that were designing them wrong then are doing it again now.

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