Sunday, March 1, 2015

Dealing with snow and ice dams in traditional roof systems

By mid-January of 2015 it seemed like Mother Nature had forgotten to deliver winter to those of us in the Northeast.  Over the next four weeks, however, Boston and other parts of New England experienced record-breaking snowfalls that would challenge season-long records in a single month.  And, with these extreme conditions, has come ice damming, water intrusion and threatening snow loads the likes of which had never been seen.

As this graphic demonstrates, ice damming occurs when heat loss causes snow to melt and slide down the slope of the roof.  As it reaches the part of the roof over the soffit, it freezes because there is no heat loss occurring.  The result is a buildup of ice that makes it increasingly difficult for melt water to escape as the ice grows in height.  The problem may be exacerbated by gutters which are clogged or don’t drain properly and, in essence, form an icy shelf on which the ice dam may grow.

Once the melt water begins to pool up it will wick back under the roof covering materials and into the building.  Ice dams must be removed without damaging the roof covering materials.  This may involve hand tools, chipping guns and steaming equipment.  The ice dams may be so extensive that the best and/or most cost effective approach is to open channels in the dams and coat the ice with calcium chloride to accelerate the melting process. 

Once this winter is over, countless home and building owners will want to make improvements and alterations to prevent future ice damming and water intrusion.  The first, and simplest measure, is to make sure that gutters, outlets, conductor pipes, and drainage inlets at grade are free and clear of obstructions.  Next, look at the way the building is insulated.  The addition of fiberglass insulation between roof rafters or the attic floor joists will make a huge improvement.  The use of closed-cell, spray foam insulation should be resisted (see more information.)

More involved measures are also available.  The use of heating coils or, “heat tape,” is often employed to keep the snow and ice over the soffit melted and the snow melt water flowing.  If you want to investigate this method further, seek and obtain quotes from three firms that specialize in these systems.  Products sold at home improvement centers, designed to be installed by the purchaser, may have trouble keeping up with even normal snowfalls.  Seek out “commercial grade,” industrial-strength systems installed by professionals, even for residential applications.

Another option is the installation of snow slides, or snow “pans,” over the soffit.  Commonly made of copper sheet metal, they form a virtually impermeable layer that ice has trouble bonding with.  While less expensive materials like galvanized steel may be used, the short term savings should be weighed against the long-term cost when the lesser metal outlives its useful service life and must be replaced.  These systems are commonly seen in Upstate New York and Vermont, and seen less frequently in other regions of the Northeastern and Mid-Atlantic states.        

Because of a general lack of insulation in their roofs, ice damming is not uncommon in older buildings. The problems that they can cause when water infiltration damages interior finishes necessitates removal and, where possible, prevention.  Care must be taken to remove the snow and ice safely and without damaging roof covering materials, gutters and cornices.  By keeping gutters clean and clear, and adding insulation, much of the cause of the ice dams may be mitigated.  Installation of heat tape and snow pans will further reduce the chances of ice dams from forming but are not inexpensive.  Always consult with an experienced, traditional building professional before undertaking such a project.

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