Vinyl Siding Nail Telegraphing

[Jerry Simon]

Seems like we talked about this before, but for the life of me. . .

It appears each and every nail head for the sheathing behind the vinyl siding is telegraphing through the siding, and readily visible outside; you can see white, round spots on the siding, same apparently coming from the sheathing nail heads behind the siding.

Attached pict shows such. What's causing this? Each neighboring house had the same thing. (No, I didn't pop any siding to see behind.)

Click to Enlarge

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[Jim Katen]

My guess: The nails are conducting heat from inside the building and forming tiny little warm spots on the siding. Water vapor condenses on the cold siding but not on the warm spots. Dirt sticks to the condensed water.

[Chad Fabry]

Cool.

[Jerry Simon]

My guess: The nails are conducting heat from inside the building and forming tiny little warm spots on the siding. Water vapor condenses on the cold siding but not on the warm spots. Dirt sticks to the condensed water.

I scoured the internet 'bout this, and heat probably does play a part. The nail heads may be too close to the siding, and the sun heats up the heads and affects the siding in some weird way (multiple theories on the internet as to exactly how the siding is affected). I tend to side with this, as the discoloration was most pronounced on the south and west sides of the houses in the hood.

It ain't dirt according to the internet folk who've tried to clean the siding (or at least "washable" dirt), but I think you're right about heat being the culprit.