Paid a visit to my attic earlier today to see if there was any winter damage. Looking all good except for a small piece of truss that has a black stain on it (see picture). I would have said mold but the symmetry of the stain is odd. Could this be a rust stain or something else that was already present when roof was built? If you look at roof sheathing nearby and cardboard piece preventing blow-in insulation from reaching soffit, it does not look like there was water infiltration anywhere nearby.

Looking for any input that you guys may provide.

enter image description here

  • what is winter damage?
    – DMoore
    Apr 29, 2021 at 15:29
  • 2
    I meant..leaks due to damaged shingles or ice dams. Maybe even condensation cause by roof vents blocked by heavy snow. Winters in Canada get nasty.
    – dstmartin
    Apr 29, 2021 at 15:36
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    I think that is paint on the lumber, but if is that corrugated cardboard under it in the photo, I would get rid of that, as it can mold. Hard to tell phone the photo exactly what it is and why it appears to be stapled to the lumber, Apr 30, 2021 at 1:41
  • (How in the world did I type "phone" when I meant "from" in the above comment? Mods, feel free to correct my comment!) Apr 30, 2021 at 6:42

1 Answer 1


Neither. It's labeling paint. It was either sprayed onto the entire lumber unit or this truss set for identification.

enter image description here source

  • Are the dark marks on the ends of a few of those pieces of lumber burn marks from the rotary saw? Apr 30, 2021 at 6:44
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    Or potentially, before being installed in the roof, that piece of wood was used to hold up something else that was being spray painted, and you're just looking at some over-spray. Either way it's perfectly harmless. Apr 30, 2021 at 13:49
  • @RockPaperLz-MaskitorCasket it's mostly natural variation in the wood.
    – isherwood
    May 2, 2021 at 0:54
  • @isherwood Thank you. I was wondering why I rarely see it in wood I cut. Probably just different species or variation of trees. May 2, 2021 at 1:09

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