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Asphalt shingles are wet in the morning

kjmass1 | Posted in General Questions on

Zone 5 – Boston

The last 2 mornings I’ve noticed my neighbors’ 3 tab flat shingles have a lot of condensation on them almost like it had rained and was drying off. That got me thinking if that is a positive or negative based on their roof build and insulation. We’ve had highs around 90 and overnight lows 65-70 with dew points around 60-65. I haven’t noticed any on my roof across the street with similar sun.


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  1. GBA Editor
    Martin Holladay | | #1

    It's called dew. Dew forms on cold surfaces. Roofs can be cooled below the air temperature if they are exposed to a clear sky at night, due to a phenomenon called night sky radiation. This cooling effect doesn't occur if a roof is shaded by trees, or on cloudy nights.

    Black roofing cools off faster at night than white roofing, so black roofing is more likely to have dew in the morning than white roofing.

    More information here: "Night Sky Radiation."

    See also: "Why is black the best emitter?"

    1. kjmass1 | | #2

      Thanks for the article, that is helpful. I realize it was dew but curious why they seem to be the only one it is noticeable with - must be tree shading on the other homes.

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