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What’s the Cause of a Warm “Bald Spot” on Roof During Snowfall?

  • Transcript

    LESLIE: Kathy in Indiana is on the line. Is dealing with a bald spot on her roof when it’s snowy out. And we’ve been getting a lot of snow this winter, so your house must look like it’s in need of a toupée. What’s going on, Kathy?

    KATHY: Hi. Yes, we just moved down here from Wisconsin, down to Indiana. We bought this house and we’ve been doing a lot of work on it. And when we got our first snow, I noticed, on the back part, there is a – like a foot-and-a-half-inch diameter bald spot every time we get a snowfall. And we had a friend – a contractor – come down. He went up in the attic and he’s like, “There is nothing going on here.” So the only thing we thought, well, maybe is going on is we have a heat pump and we also have our dryer vent in that same area back there.

    And so now I had two different suggestions. He said to put a soffit venting on that whole area to get more air going up through there and possibly maybe it’s coming from the heat pump. But then I went to The Home Depot and I was talking to the guy there that seemed to know quite a bit. And he said – and what he would do is take it and remove all the vented area – vented soffit in that area. And so if there is heat coming up – he said, “But this shouldn’t happen.” He said, “This is what people do. They put their heat pumps outside.” And he’d never heard of anything like this before.

    So we ended up doing that and so we don’t know yet if that actually helped it or not but …

    TOM: Yeah, it’s not hurting the roof not having snow on that one spot. If you want to know why it’s happening, it’s because that spot is warmer than the other spots around it. Now, why is it warmer? Well, you mentioned there is a dryer exhaust duct near there. If the dryer exhaust duct is not completely sealed, if it’s dumping warm air in there, that’s going to heat up that spot over the roof and then any snow that hits there is going to melt and roll down. If the insulation has some gap in it of some sort in there where more room air can get up and heat that area right above it, that could cause it, as well.

    But I would not tell you to start messing with your venting and everything else just because you’ve got a foot-and-a-half spot that doesn’t – where snow doesn’t stick. It’s curious but it’s not a major problem and I wouldn’t recommend major work for it.

    KATHY: OK. So it’s – we don’t have to be concerned that there is heat getting up there and it’s going to cause mold and issues going on?

    TOM: Well, I mean I would try – I would determine if there’s an obvious source of warmth that’s getting into that spot. But actually adding heat to that area is not necessarily going to cause mold. You’ll get more mold in the less heated spaces, frankly. Because when you warm moist – when you warm air, it uses more moisture, essentially. That’s why the warm air holds more moisture, so that’s not really a concern. It’s just kind of a curious thing.

    And if you’ve got a dryer vent that’s right near there, I’d start with that because that would make perfect sense. If the dryer vent is losing some of its air right in that space, that’s not a good idea, either, because you don’t want to be dumping any lint into the attic. That could be dangerous, OK?

    KATHY: OK. Well, very good. Thank you.

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