Saw this on the exterior around a bathroom and/or laundry vent.
Is this just mold because the vent can’t open?
Thanks.
Mark
Mildew/mold growth due to frequent and slow expulsion of humid air. If it’s a dryer vent, although I see no signs of lint, it could be clogged.
If he was doing his job he should have ruled that out. ( ladder ) Dryer fire?
You need to know if it’s a bathroom or laundry vent (dryer). I’m with Kevin looks melted.
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It also looks dented?
did You look in the attic ?
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My bet is soot from burning candles in the bathroom and running the fan.
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You sexy guy you, Taking candle lite bubble baths. 
JMO, but it appears that it is the termination of a dryer vent. I have yet to see the louvered vents used on other types vents, but that’s not to say they are used for other venting. We see it all. The louvers on the vent are distorted and most likely stuck in place, the reason the discoloration is forming the way it is. It appears that it is blowing out of the sides of the housing or stuck louvers.
With that said, I would recommend, replacing the vent cap and have a licensed HVAC/ Plumber to determine the cause of the discoloration of the siding.
Things like that require a closer look. I, too, think it looks more like smoke and scorching than mold. The pattern doesn’t have a typical mold look. Look at the discoloration on the fascia. Frankly, that looks really bad and my red flag alert is waving.
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If it’s from a bathroom vent the candle thing might be it, but just as likely is that someone has been getting baked on the reg in that bathroom and blowing the smoke into the fan. No matter what I’d write it up. Remember we don’t need to necessarily know what caused a defect but simply that it exists. That being said I’d recommend examining the fan for defects, clearing the vent pipe and changing the fixture on the exterior.
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Mark, it is kind of like ghosting, where warm moist air hits the outside cooler air and collects the dirty/potentialy spore filled air and it sticks to the damp siding. I would bet it is a fan vent termination from a bath or such…IMHO.
We power wash our house every 2-3 years to remove stuff like that…it comes right off.
And, I bet, the louvers are disfigured because they are flat and have no reinforcement strong backs on the inside of them. I just replaced one of mine because it was as I described and got a lot of sun and is on the prevailing wind side.
Can you post the homes ventilation equipment, energy source for heating and any pictures of duct work in the attic, and the gable end insulation, or lack thereof, please.
As for the atmospheric grim. The aluminum fascia cladding has residue even though drip edge was installed at the gable. Warm air risers.
Lint fire.
Possible dust from blown in cellulose insulation?
Looks melted. Don’t see how a bathroom vent would melt.
too many burritos…
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At that point we didn’t know if it was bathroom or dryer. So I guess you’ve never seen melted siding?
This thread needs a knife put in it, The OP could have figured this out on-site, soot or mold? bath vent or dryer vent? I guess he don’t have a ladder. Crazy, why was he there?
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