Any idea what would cause this?
I think this has to be something on the structure behind (tape or something) that’s affected by the atmosphere (heat?) and showing up as discoloration. If you pull off a piece of siding, I’ll bet the cause of it will be easy to identify. I rarely disconnect siding and look behind it, but in this case (and in the summertime) I would. If I saw it in the wintertime, I probably wouldn’t to avoid the possibility of breaking the siding.
It could be caused by a few things. The staining looks like it lines up with the weep holes in the vinyl siding. Depending on the age of the home it might not have a WRB behind that siding. WRB was not required until 2006 with vinyl siding and that could be part of the issue as this increases the amount of air leakage in the home which can cause what you are seeing. Or it could be; a poorly installed WRB, no or minimal insulation in that wall which could also cause that.
Did you put a moisture meter on the interior wall or use an IR camera to see if it showed anything?
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My WAG is dirt along with high humidity.
Notice the upper rows are dirtier than the lower rows, maybe because the lower areas are exposed to rain and wind driven rain.
Did you try to clean any of the staining/dirt off?
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Thermal bridging at studs. Condensation from high OA humidity.
Happens in cooling season. There will be moisture behind the siding. Check what Scott said.
Note the V pattern. Dripping water makes an inverted V.
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No one has mentioned the possibility that someone made a lousy attempt at washing the house, and water got behind the siding and dripped out the weep holes.
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I still see tar paper/underlayment being used as the WRB… add mositure… air movement… draining from weeps… VOILA’!!
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David mentioned dripping from weeps correctly, IMHO.
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Larry, you are not reading the treads correctly, Dave did not mention weep holes, and I was saying someone may have washed the house. And as far as the felt paper goes, I have never seen a problem with it behind vinyl siding if the siding is installed correctly.
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So, are you saying weeps DON"T make an inverted V unlike the pic the OP posted?
Because washing the house would make inverted Vs of dirt. Not Vs of dirt like the OP pics.
You never know what accumulates behind vinyl siding.
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Guess you never came behind someone with a pressure washer.
Let’s get back to the main subject of this thread:
There are only three causes of water in a building, a hole in the building envelope, a broken plumbing pipe, and condensation.
Vinyl siding is not waterproof. It is only cosmetic.
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The material is waterproof, the installation is not…
Again, I’m suggesting condensation, which has to do with air infiltration, not water.
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Look at the bottom of the gutter pans and soffiting. Atmospheric grime is washing down the wall.
As for the localization, likely the contours of the siding.
Cause prior or present dirty clogged gutters.
I can give you pictures of gutter leakage. They are not a V pattern, rather a straight line in most cases.
If the gutters are leaking behind the vinyl siding, that would be another situation.
Because they are 16" on center, I stand with a condensation issue.
I blew up and enhanced the pic’s and I see no weep holes.
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It looks like soot to me. Is there a wood or oil burning appliance nearby?