Stains Peeking Out of Siding Planks

I’m interested in your thoughts, observations, and comments you would write up if and when you see this sort of thing. There are stains that appear to be some water that surfaced from underneath the plank or planks above. BTW, the roof looks great.
IMG_5263 IMG_5265

It looks like remnants from power washing the siding, to me.

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Need zoomed out pics and more info, could be a number of things.

Try this:

At least I was consistent this time. :grin:


I did not think of power washing. That is very plausible. Particularly when washing from below, it is easy to force water up and under the planks.
That is good insight.
Some years ago, we had gale force winds in a blizzard that drove snow under the north facing siding on the barn and then when it warmed up, water trickled out like this, but these areas on this home would be sheltered from something like that.

Is it wood or wood composite siding? Here in the South, it’s common to see stains similar to this made by the the dust created by Carpenter Bees. The dust seems to adhere to the wood and the moisture from the rain will actually make it set and stain the wood.

Also see the holes above the stains.

Just a guess…

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Composite siding. No carpenter bees here. We don’t have many of the destructive pests that you see in the south. Termites are so rare here, that termite inspections are not required and rarely done.

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Well…back to head scratching here…

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It could be from washing the house or a poorly insulated house with indoor horticulture, condensation?


Some years ago, we had blizzard here that drove snow under the Hardie planks on our barn. The previous owner had built the barn and while I was pleased that he used Hardie, he didn’t wrap the barn (or the house, for that matter) and melting snow drained on the inside of the OSB sheathing as well as out from under the exterior facing planks. The incident more than convinced me of the merits of some kind of exterior water proofing system under the siding/veneer.

Bats in the eaves?

I had this happen this summer, my shed started sweating and under the siding and dripped down, my only guess was that I did not install a vapor barrier between layers and the color came from the plywood sub wall component. no evidence inside though.

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Is it spray foam insulation?
It is common to see staining at double studs and rafters where the foam doesn’t cover
Path of least resistance for moisture and heat loss is at the seam in the joist studs rafters