Are icicles unavoidable? Roof color an issue?


Old 02-17-14, 10:38 AM
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Are icicles unavoidable? Roof color an issue?

I have lots of insulation in my attic but still getting icicles. Are icicles unavoidable when we have weather like this in the northeast?

Are there rules of thumb as to how much eaves ventilation you should have? And vents at the ends of the house? Seems like more them merrier (no such thing as too much?)

I have a remote thermometer in the attic and like seeing that it's much closer to the outside temp than the inside temp. That's good right? Are there guidelines about that? ( attic temp should be no more than x more than outside temp when its cold outside? Or is the heating of the sun on the roof in the winter too hard to take into account? Or check at night? Seems light colored roof would be better in general? I used to think dark roof in the northeast is good beause it will absorb heat / lower heating costs? but the attic insulation will keep the heat from getting into the house anyway. it will just heat the roof, melt snow and lead to ice dams? Light color would keep roof cool in summer and winter?
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Old 02-17-14, 11:14 AM
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Roof color, orientation,pitch,length of slope, number and size of valleys will all contribute less or more to ice issues. Is there ductwork in attic space? Of course all of the issues regarding air leakage from living space to attic are also critical.

You are going to find that in many cases, even with insulation and ventilation to code, extremes of weather will bring about the shortcomings of an assembly.

I even see icicles on roofs sprayed with foam. And foam may give you other concerns such as limited snow melt which contributes to increased load on the structure with possibility of structural compromise.

I've always been a fan of metal for the first 2'-3'of roof edge and raking the snow off the edge of the roof where the gutters and roof edge seem to work together to develop the problem. Short of good luck, use ice melt cables.

One of the better practices I see is the use of a raised heel truss or a ceiling assembly with a rim at the edge of joists to give increased space for insulation and a greater clearance for ventilation.
Old 02-17-14, 05:05 PM
Join Date: Oct 2008
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The rule of thumb for ventilation is 1 sq ft of NFA (net free area) for every 150 sq ft of attic floor. If extreme efforts have made the attic/ceiling plane air and moisture tight then half of that number. Then the resulting vent area is generally divided half high and half low. Note, few home achieve a well sealed attic floor plane. Also, the soffit ventilation needs to easily access all rafter channels.

The solution to ice formation is air sealing that attic floor/ceiling and lots of insulation. Done right the ventilation is not as necessary. With all of that insulation already in place, target as many of the major leak sources as possible. A complete sealing effort would be difficult. See link below:

Shingle color and reflectivity are part of the equation to be considered when you eventually replace what is there.

If you have gable vents they will work if large enough. More is better until mother nature starts blowing the rain and snow in, which varies with each house and location. A ridge vent in combination with what you have would be best.
BSD-135: Ice Dams — Building Science Information

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