Do Icicles Mean Bad Insulation?

Origins

• The most important cause of winter icicles is loss of heat from the interior of your home. As the heat escapes into the upper story or attic, it eventually reaches the roof. Packed snow and ice melt, both from this escaping heat and from solar energy that strikes the exposed portions of the roof during the daytime. Water runs down the roof and over the gutter or roof line.

Formation

• In the process of falling from the roof, meltwater will freeze and accumulate as ice when temperatures are low enough. As a result, an icicle begins to form at the roof edge, growing downward as more water falls and freezes. The longer the icicle, the greater the volume of water feeding it. Some icicles can grow several feet in length and remain intact for weeks or months as winter's freezing temperatures continue.

Insulation

• If your attic insulation is poor, more heat will escape from the roof and more melting will occur. An ice dam will form at the edge of the roof, causing some of the meltwater to back up into the eaves and underneath the shingles. Eventually, this will cause a leak into the living spaces, either from the ceiling or walls. Icicles also damage gutters, shingles and the roof decking; water leaking into the attic can also cause mold and mildew.

Prevention

• A well-insulated home should not have a large number of icicles, and keeping the roof clear of snow will eliminate icicles altogether. If you spot icicles forming, you should attend to your home's insulation, and of course ensure that the icicles aren't large enough to threaten injury to anyone on the ground should they fall.