Icicles tend to be the stuff of holiday cards. Pretty to look at and reminiscent of bygone eras, they are essentially stalactites of ice. They decorate the eaves of a snowbound home with an air of beauty and provenance.
However, while they are inarguably beautiful to look at, they often indicate an underlying problem: heat is escaping through the roof. It’s not always the case, but leakier and poorly insulated older homes tend to excel in this department.
Generally speaking, icicles are the product of melting snow. However, the snow may not be melting because the ambient air temperature is above freezing. Rather, it’s the air beneath it–the air in your attic. As the attic air warms the roof deck, the solid snow liquifies and starts to trickle down the shingles into the gutter or eave (this can also create ice dams). At the eave, however, the air returns to freezing and that water once again becomes solid, this time as ice. As more water makes its way to that spot, the droplets become larger and larger until they’ve formed an icicle.
In some cases, snow can clog gutters and, whether the snow is melting because your roof is leaking air or because the air temperature rises above freezing then falls again quickly, the result is icicles: the gutters have filled with snow and water and the melt has to go somewhere (assuming the gutters don’t fall off), which is over the side where it immediately freezes and becomes an icicle.
If you have icicles forming, they may be forming only in certain areas of the house–the leaky parts–and can be a guide to where you might want to beef up insulation. If they’ve formed all around your house, you probably have ice dams as well which may lead to big time roof leaks.
After all, holiday cards are designed to bring about warm feelings with fictional art. Houses have a much tougher job living in the reality of a world where heat is not free. Plus, you can save money to buy me a present.