The Ice Dam article in the September/October 2011 issue of Minnesota Community Living by attorney Matthew Drewes discussed some of the most common causes of ice dams, including inadequate ventilation within the attic and air leaks (bypass air) from the living space into the attic, as well as answers to some other common questions about what owners and community associations should do about this problem. The article also mentions other potential causes of ice dams such as inadequate insulation and heat loss from ventilation systems, but people may not realize all the reasons a properly-insulated attic is possibly the second-most important way to prevent ice dams (other than sealing air leaks). This article goes into more detail about how to spot these insulation issues and what can be done to correct them.
There are two primary aspects of inadequate insulation:
1. insufficient insulation depth, and
2. compromised insulation.
These conditions may have similar remedies depending on whether or not air leaks are present from the house to the attic.
Prior to about 1985 the amount of insulation in new residential attics was about R-22. Since about 1986 many attics had the air leaks sealed and insulation installed to a level of about R-44 (about 17 inches of blown fiberglass, or about 14 inches of blown cellulose).
Residential property construction practices before about 1985 typically did not include any attempt to seal air leaks from the house to the attic.
Buildings built before 1985 which have been re-insulated to modern levels without removal of the original insulation and sealing of the air leaks have a high potential for moisture damage to the roof sheathing due to warm air from the house condensing on the sheathing during cold winter nights.
Some modern townhouse buildings with an adequate original amount of insulation have been suffering from excessive heat loss and ice dams due to compromised insulation and air leaks to the attic. Blown attic insulation is easily compromised, when it is compressed or displaced by human foot traffic.
Mice also compromise insulation with tracks and/or tunnels, which are quite common in Minnesota attics.
Attic insulation can also be disturbed by misplaced and/or unbaffled attic ventilators which may permit wind to blow the insulation around in the attic.
A fourth cause of ice dams, which is unfortunately becoming more common in Minnesota townhouses, is the installation of supply air ducts in the attic. The presence of heating ducts in the attic can lead to conductive heat loss to the attic from inadequate insulation over the duct and/or convective warm air leaks from punctures, damage, or loose connections in the ducts. These conditions can often be identified by use of an infrared thermal camera.
Home owners and home owner associations are advised to adopt practices that restrict access to attics and require cable or satellite TV installers, electricians, or others who enter attics to be responsible for correction of any damage to or disruption of the attic insulation.
One way to develop long term remedies for ice dams is to work with an experienced inspection firm to investigate all the causes of the ice dams. The causes of heat loss may be different in each unit, even in the same building. Often the recommendation for best results will be to remove all the existing insulation to permit finding and sealing all air leaks into the attic before re-insulating.
The good news is that most of the long term remedies for ice dams have the added benefit of significantly reducing heating and cooling costs, and may even extend the life of heating and cooling equipment.