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Staining above crawlspace vents


scrump747
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Hello All, From a newbie on this forum...

Has anyone seen or can you explain...

On a grey house, stucco siding, crawlspace.

Above the crawlspace vents (only on the southwest side of the house) there is what seems to be staining on the stucco from some vapor rising out of the crawlspace. There are vents all around the house, and there are only 3 vents that show this staining. The furthest southwest is the worst, and as one moves north, the staining gets progressively less, until the 4th vent shows no staining. This house is in Danville, CA, an area noted for its very hot and dry summers and relatively wet winters. The crawlspace was moist upon inspection. There is not a furnace or anything else other than plumbing and HVAC ducts in the crawlspace...Thanks. mark

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It sounds like the prevailing wind is creating that issue by forcing most of the crawl space air out through those particular vents, but what the stain substance is would be anyone's guess. I would normally think very fine, powdered dirt or mildew, but that doesn't sound like what you're describing.

Brian G.

Bug Farts? [:-slaphap

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How about this?

The air exiting the vents is causing a bit more moisture around some vents. Dirt particles in the air then adhere to the moist areas at a greater rate than they do the the surrounding areas that are a bit more dry on average.

So its not so much where the dirt is coming from, but more that dirt sticks better to wetter surfaces.

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Originally posted by SonOfSwamp

Originally posted by AHI

How about this?

The air exiting the vents is causing a bit more moisture around some vents. Dirt particles in the air then adhere to the moist areas at a greater rate than they do the the surrounding areas that are a bit more dry on average.

So its not so much where the dirt is coming from, but more that dirt sticks better to wetter surfaces.

Don't go by me, but I wouldn't say that because I don't think there's any way for an HI to confirm that, unless he actually measures humidity at the vents, samples the "dirt," etc. And even if he does all that, conditions will change frequently, prolonging the mystery.

It's all totally meaningless anyway. Schmutz happens. If it bugs the homeowner, tell him to wipe it off. TSP, warm water, soft brush...

WJid="blue">

Walter, you said some kind of particulate is coming out of the vents. My point is, maybe it's not. If I can't prove what I said, you cant prove what you said either. I go by you, thats why I engage. HI's do say things that they can't confirm sometimes, don't they?

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Hi,

Well, it's the initial poster that's claiming that the staining is being caused by vapor coming out of the crawlspace and, frankly, I think he's wrong. I don't know what's causing it, but I don't believe it's caused by crawlspace vapor. He says it's stucco-clad. I can't recall ever seeing dark stains above crawlspace vents here and, here in the northwest, we've probably got the dampest crawlspaces around.

I certainly would have written up any moisture issues in the crawlspace for correction but I doubt it would have changed the way the cladding is becoming stained.

Looking at it from the standpoint of the cladding that was used, I suppose it's possible that, if the vents pass through the stucco cladding, that the stucco guy didn't install weep screeds above the vents and used ordinary metal termination beads above the vents that don't weep. If that's the case, stucco is porous and will absorb a certain amount of moisture; that moisture then needs to drain to the base of the wall and escape. As that moisture moves downward and encounters the vent terminations it's forced to either side of the vents, causing more moisture to be present in the stucco immediately above the vents. Dust blowing around outside might be clinging to the damper stucco.

That's a possible theory, but without seeing the house and being able to examine the stucco I don't think it's a theory that one should voice to the customer. Frankly, if I'd seen it I'm not even sure I would have bothered to comment about it unless I saw it as the basis for some other issue. The weather does come from the southwest here on the left coast, so I suppose that, if there aren't proper weep screeds I'd have a basis for a theory; however, I'd hold that theory in check until I could talk to some stucco guys - the Northwest Wall and Ceiling Bureau (www.NWCB.org) for instance, and confirm the theory before I offered it.

If, there aren't weep screeds over the vents and, based on talking to NWCB and others, I thought I'd figured it out, I probably would have only written up the lack of weep screeds as an issue and would not have bothered to go into the darkened stucco or any of the other theory because it would only confuse the issue.

ONE TEAM - ONE FIGHT!!!

Mike

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Maybe the same kind of staining one sees on a roof coming out of roof vents?

Often, I'll find darkening around all sides of several roof vents on the same home. I don't think anything of it nor do I say anything.

I just sign it off as some kind of stuff coming out of the attic. Way too scientific for me and it's not doing any harm.

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