Why does my house have ice dams?

Every climate type poses its own set of challenges to overcome.  In a cold weather climate, where snow and ice are common, it is not unusual to see icicles hanging from the eaves of a home.  If you are interested in the well being of your house, it is worth your time to understand how ice dams form and how their presence can impact your house.

What is an ice dam?

Icicles are formed at the bottom of a roof when water suddenly gets cold enough to freeze.  The water running down your roof from snow melt or a rainstorm can sometimes reach the bottom of the roof and freeze where it is most exposed.

These large frozen masses can put weight on a gutter system that was not designed to hold that kind of weight or, even worse, lead to ice dams, where the frozen mass can get underneath the roof covering and potentially damage the covering or even the roof structure.

Icicles and ice dams are a symptom of a larger problem with the house where the roof covering is warmer than the eaves, even in below-freezing temperatures.

What causes Ice Dams?

Ice dams are caused by poor insulation and lack of proper ventilation in an attic space.  If your attic insulation is poor, the heat from your house will rise to the attic space and warm the roof deck and roofing material.  This will cause falling snow that lands on your roof to melt quicker.

The snow melt will then run down the roof to the eave, which is more exposed and not close enough to the warmth of the attic space, which then causes the snow melt to freeze again.  Similar conditions can arise in a house with adequate insulation, but very poor attic ventilation, as the attic space will retain heat and warm up the roof deck and roof material.

Additionally, a home with poor attic ventilation can result in condensation forming on the underside of the roof deck.  If you were concerned about water getting into your attic space, you probably think about the roof covering first and moisture coming from outside.  However, it is not uncommon to see moisture staining and damage inside an attic space from poor attic ventilation.

Preventing Ice Dams?

Without minimizing the potential damage that ice dams at the eaves and condensation on the underside of the roof deck can have, this is a simple problem with a simple solution.

Increasing the attic insulation and improving ventilation will keep the roof deck and roof covering at a consistent temperature, preventing falling snow from melting easily, causing ice dams at the roof eaves.  The ideal house will keep each part of its roof deck at a temperature near the outside air temperature so that there is no sudden melting and re-freezing occurring anywhere on the roof.

We will sometimes see “heat coils” installed on a roof to melt ice dams that build up over the winter.  This is an installation that treats the symptom, not the condition. Review insulation levels and ensure proper ventilation of your roofing system, to address the root-cause of ice dams on a home.

If you are interested in knowing more about the insulation and ventilation of your attic space and how these systems can affect your home, we recommend that you consider having an Energy Audit performed by the energy efficiency specialists at Scott Home Inspection.