Ice Dams and Winter Woes

What a winter this has been in New England! Storm after storm and continued cold weather. This combination has wreaked havoc on so many homes it is hard to count. Loads of snow on roofs and ice dams clogging gutters and creating massive ice features. They may be visually stunning, but are causing extensive problems for building owners.

As an architect, I get many calls as to what to do. The immediate strategy is to get as much snow off of your roof as possible. I have received dozens of faxes from companies soliciting their services to remove snow and ice. Be wary of unsolicited companies. It is always best to find a contractor or roofer that you know or that may be given as a reference from someone that you know. If you are determined to do it yourself, exercise extreme caution, and use a snow rake to get rid of loose material. Climbing on icy roofs is not a good idea. Care should be exercised to pull downward so as not to dislodge roofing shingles.

Removing the ice is a harder task. With care, dripping icicles can be knocked off, but the ice that has formed in the gutters can be intractable. Hacking at the ice with hammers and axes can damage gutters, trim and roofing. Some suggestions are to use nylon stockings filled with ice melt, placed over the ice formations.  Ice melt comes in many formulations- calcium chloride, magnesium chloride, or rock salt to name a few. Calcium chloride is noted to have the best result with a lower melting temperature. I have tried this method, but find it to be less effective than suggested. This is likely due to the extreme cold temperatures that we have been experiencing this winter.It has also been noted that these salts can interact with flashing and fasteners, but that is a risk that is likely to be chosen when water is leaking through your roof. One viable method is to use steaming equipment to melt the ice dams. Companies normally working in the mid west have flocked to New England and are working around the clock to relieve our massive ice build-ups. They will typically charge hundreds of dollars per hour, but the decision of cost must be weighed against the potentially large cost of repairs due to water damage.

Consider the source of the ice dams to prevent future formations. The key to prevention is to keep the roof cold. Ice dams form when the upper sections of a roof warm and melt the snow. As the melting water reaches the cold eaves, it freezes and forms ice build-up. As this cycle continues, the water is pushed back up-hill, under the roof shingles and into the building enclosure. 

 

Courtesy of Univ. of Minnesota www.extension.umn.edu/

Today there are three basic methods to maintain a cold roof. The most historic practice has been to apply insulation to the attic floor and lower level walls, maintaining a vapor barrier to the warm/room side of the assembly. With this strategy, cold attic air must flow from ridge to eave. If there is insufficient insulation, air leaks or blockages, the roof may become too warm. 

With cathedral ceilings or finished attic rooms, the insulation must be placed within the plane of the roof structure. Under this scenario, the vapor barrier is located behind the ceiling finish, on the warm/room side of the assembly, with insulation over and an air space maintained by the use of vent chutes between the insulation and the roof sheathing. This method requires a combination of eave and ridge vents to allow cold air to flow under the roof to keep the temperature from rising.

One of the most current insulation techniques is the use of spray foam. Energy codes are now requiring greater insulation values in roof structures. Foamed insulation provides a greater R-value per inch, making it a more viable choice for roof applications. Open cell foam still requires a vapor barrier beneath. Closed cell foam has the higher R-value and forms its own vapor barrier. These can be applied without eave and ridge vents and are installed to form a continuous thermal layer. Again, it is important to provide care to prevent cracks and locations where air leakage can occur. Newer methods apply the insulation on the outside of the roof/wall structure and sheathing, but that is a topic for further discussion (see http://www.buildingscience.com/ for extensive methodologies on exterior thermal enclosures).

If you have had the unfortunate experience of water leakage, you will not only have to consider the cosmetic damage, but also possible issues within the wall/ceiling cavities. If older insulation products have become soaked due to water infiltration, as the season warms, mold may have a chance to form.

With care and attention to detail, this problem can be addressed. Hopefully the remaining winter weather will be a bit more relenting.