Dry water staining on house side of eave. Thoughts?

Specific Inspection Topics Roofing Inspections
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West coast of Canada in moderate climate that doesn’t freeze often. 2013 build. 3 bed, 2 bath rancher with architectural shingle roof. Roof appeared to be in good condition. Roof sheathing in excellent condition with no signs of water or staining. There is 12-14 inches of blown fiberglass insulation with poly standing vertical to hold it back from the non-insulated garage ceiling.

I’m seeing dry water stains (although we are in dry season) on the house side of the eave. There are no water stains where the eave meets the fascia/gutter. Assuming they used poly to hold back the insulation from the eave as well, I’m guessing that this is likely from condensation where the insulation is warm in the cold season and the humidity in the air is condensing on the exterior of the poly and dripping down to the soffit.

Would like to hear what others think as this is first for me. Thanks in advance!

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Any photos of the roof and attic?

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I can see any soffit vents.

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Soffit vents are perpendicular from the exterior wall to the eave. Pic is from a different issue but shows the soffit vents.

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Likely the end grain was not sealed. As well not venting.
That’s my wag.

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My 2 cents. This is due to air movement or vapor transfer. Differing materials promote it.

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This is roof, flashing, or gutter related.

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Evening, Brian. Hope to find you well.

I concur. Likely the rotted wood and fastener corrosion is likely due to drip edge flashing not preforming well or clearance, lack thereof.

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As for air movement or vapor transfer. Moisture vapor transfer rate, or MVTR, is a scientific measurement quantifying the amount of water vapor or body moisture that can pass through a fabric or garment. Or WRB. I would not say that IMO.

Thanks.
Robert

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First, I said nothing about MVTR.

So, what would you say? What is your diagnosis?

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My 2 cents. This is due to air movement or vapor transfer. Differing materials promote it.

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Bulk water or vapor condensation… I wonder what the interior wall and ceiling are. Is the air barrier monolithic? From the moisture condensation approach: Possibly interior air barrier / moisture barrier issues where the wall and ceiling meet. Possibly no wind wash barrier at the juncture of the eave and interior wall can be a factor.

I wonder if there is evidence of ice dams on the roof. Equally as suspect, that’s a bulk water source.

More technical analysis and further exploration of the roof and attic are needed. Testing for air leakage at that area for one. Infrared imaging with blower door prudent. Both will provide evidence re condensation.

Thorough roof inspection; ice & water shield present or not? Roof and attic - evidence of ice dams? Ask seller about history of icicles or ice dams.

For the HI, I’d report moisture stains, moisture meter reading xx%, recommend further evaluation. May be a bulk water or condensation issue.

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