Roof insulation and snow melting


I'm confused about something. I've always heard that you can tell how good the insulation is in the attic/roof by how long it takes for the snow to melt off the roof. Does good insulation in your attic/roof make the snow melt off quicker or does it take longer?
I tried looking at different roofs in the area to figure this out but it only confuses me more. For example, my garage and shed still have snow on them but my house doesn't. Sometimes a neighbors (much newer) house will have snow on the roof and mine won't have any. Then I look at another shed that has no insulation and is somewhat in the shade and it has no snow on the roof.
When I searched on Google, that confused me as well because unless I'm reading something wrong (I probably am) it's saying that my shed has better insulation than my house! BTW, the roof of the garage and house are both facing the southwest and the garage roof is only slightly lower than the house roof.
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Typically good insulation will make the snow and or frost last longer on the roof. If you have a garage that's uninsulated, without a ceiling, the interior/roof will generally be the same temperature.
You can also tell a lot about the health of your roof and attic by looking up on the roof regularly. For example if you have a spot near the eave that constantly melts but there's snow above and below, you have insulation/ventilation issues. This leads to a whole list of more questions, is there vent space between the insulation and the roof, is there adequate ventilation from the eave to the peak?
Here's a link on ice dams that explains a lot about roof ventilation: <http://www.buildingscience.ca/documents/digests/bsd-135-ice-dams/2006-10-30.2876199823/download and another for some great information on heating and ventilation: <http://www.buildingscience.ca/buildingphysics/thermalcontrol/heatflowbasics
If you suspect issues and are able, crawl into the attic and see what's going on...
Good luck,
DAC

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For the rate of snow melting to have any relation to insulation, the space underneath has to be heated, like the living space of a house. If the insulation is lacking, enough heat can rise to the roof to make it melt faster. However, even here a lot depends on other factors too. If the roof is poorly vented, it will likely melt faster, as little outside air can work it's way inside. And obviously the exposure the roof has to the sun is going to be a big factor. A roof facing southwest is going to melt a lot faster than one facing north. The garage roof is going to take longer to melt, because there is no heat in the garage.
The unheated shed in the shade may have had less snow to begin with, being blocked by trees perhaps?
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wrote:

The house wastes heat thru poor insulation. The heat melts the snow on the roof. So the longer the snow stays on the roof, the better the insulation.
As soon as enough snow melts for sunlight to hit the roof, then all bets are off - because some roofs absorb much more heat than others.
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If you kept your house as cold as the shed and garage get, you wouldn't see that difference. :-) The garage and shed have no heat to lose through the roof to melt that snow.

Conclusion: the neighbors have more attic insulation and or more soffit or ridge ventilation than you do. This is a datapoint worth acting on.

Is the shade caused by the proximity of another structure that's keeping it from getting snow?
This is a datapoint worth ignoring.

I think you just failed to consider the notion of needing heat before heat loss becomes apparent.
Best Regards, -- Todd H. http://toddh.net /
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...

Other responses are good, I'll just add that if the exposure and amount of snow caught are even approximately the same on the two houses, it's a reasonable bet that owing to the fact the neighbors' house is newer it probably is better insulated and more tightly sealed than yours. It's pretty likely with these symptoms that more attic insulation would be a discernible cost-saver. Most utility companies have programs for energy assessments that are either of no or fairly low cost or at least have lists of companies that do them that have been screened. Might check in on that as a starting point. It might be there's even some cost-share for any upgrade/improvements you make.
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wrote:

Roofs can heat up but the 'cold roof' concept heavily relies on roof ventulation. If there is no ventilation, then what ever heat gets into your attic space, will build and build, and cause the snow to melt.
Just might want your ventilation checked.
tom @ www.Consolidated-Loans.info
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Mike S. wrote:

Heat rises, so if the snow is melting, there is little insulation in the attic. In other words, good insulation prevents snow from melting.
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