It's wintry and pretty outside with the recent snow and now sunny skies, but those glistening icicles hanging from the roofs of some houses signal more than just ambiance.
Ben Weil is a building scientist and the director of Climate Action and Project administration for the City of Northampton. He knows a lot about building envelopes and what damage can come from those icicles.
Weil says when people talk about problems with ice dams, they're essentially describing the action that is caused by heat loss, compounded by the insulating effects of snow.
"Ice dams happen when there is enough snow on a roof, that the snow is functioning as sufficient insulation to cause the roof surface to be above freezing, so that it melts the snow from below," he says.
And most of those roofs with issues are sloped roofs where the now liquid water will flow down to the edge that overhangs the walls of your house, called the eave.
"Which is no longer over the building that's losing heat, " says Weil, "And so now the roof is below freezing at that section of the roof. And so, the ice forms."
And as it forms, it creates a dam that holds back more liquid water that freezes up, gaining mass. Eventually, because the ice dam is growing, it will rise up and get under the roof's surface.
"And ironically, of course, the more snow you have, the more insulation you have. And so the colder it can be outside and still melt snow at the roof," he explains.
Weil says homeowners should look at their eaves, because that's how you can tell where the dreaded ice dam will form. That's where the pretty icicles are.
'[The] decorations that we see [icicles] are indications that you are melting snow on your roof," he says.
The weather this time of year is sort of the sweet spot for forming ice dams.
"The other factor," Weil says, "is how cold is it outside. So, when you're pretty close to freezing but still below freezing, that's the optimal time to form ice dams. If you're above freezing... obviously, you can't form an ice dam because you're not going to freeze any of the liquid water!"
The good news is that he says more modern houses that have R-40 or R-50 insulation, probably have enough to prevent getting an ice build up unless there's more than a foot of snow on your roof. But even houses with adequate insulation could have small air leaks, and those will be apparent by the icicles hanging from the eaves.
Weil explains, to prevent ice dams, some intervention will be needed, "We're actually taking warm air from inside ...and it's rising through whatever hole [is] connecting the inside of your house to the attic. And so the best solution is to look at that spot. See if you can find it on the inside. Usually that means crawling up into an attic. Pulling away the insulation and gun foam sealing it."
Weil says not everybody can safely get to their attic and do what needs to be done. That's when homeowners should call in a professional. He says there's also a pretty good chance the fix would be financially covered by MassSave, a home energy assessment group.
So the moral of this, is to look for those beautiful icicles.
"Use it as a diagnostic tool to figure out 'Where do I likely have either gas insulation or even more likely, big air leaks?' " Weil says.
And consider yourself lucky if ice is not affecting your house right now.
Ben Weil studied and formerly taught on the subject of building envelopes at UMass Amherst for more than a decade. He is a building scientist who lives and works in Northampton.
