Green Needham and Next Step Living presented the first in a series of one-hour Weatherization Seminars on January 23rd, 2012. Our inaugural topic was ice damming. Those long icicles hanging precariously off the edges of roofs can cause significant long-term damage to your home and health. The presentation by Travis Estes of Next Step Living covered the causes of ice dams, the consequences and potential preventative measures available through the Mass Save Home Energy Services Program.


Ice damming is the result of heat escaping through a poorly insulated attic that is lacking air sealing.  As the heated air is pushed up towards the roof, thermal bridging leads to heat transfer that begins to melt the snow resting on roof.  As the snow begins to melt, it travels down the roof towards the eaves, which are still typically below freezing.  As the melted snow meets the frozen eave it begins to re-freeze, creating the signature icicles, along with the pooling of water where the ice meets the melting snow.  This pooling often leads to water seeping into the house, to the attic and through the walls.  Once in the walls, this moisture begins to erode wood, compromises electrical wiring, and can create a mold issue, which reduces indoor air quality.

Air flow – the stack effect

The Law of Thermodynamics tells us how heat moves and in what general direction it will move in a given situation.  A home is fairly simple to understand.  As cool air infiltrates the basement and other low leaks, warmer air is pushed upwards.  This movement is dependent on two variables:  how much air can get in and how much air can get out.  The easier it is for air to escape, the more dramatic this movement of air will be, a phenomenon known as the stack effect.  With that in mind, we need to consider how and where air escapes.  Homes lose the majority of their conditioned, heated air through the attic through gaps associated with plumbing and electrical penetrations, top plates of walls, chimneys and bath fans, and attic accesses like pull down stairs.  Heat is also lost through thermal bridging, which occurs when a thermal mass like framing or ceilings conduct heat from one side to the other.  In each instance, there is a proper treatment that can dramatically reduce, if not completely eliminate ice damming all together.

Prevention – air sealing

  • 100% covered by the Mass Save program if specified during the energy assessment
  • Expandable Polyisocyanurate Foam (Spray Foam) to seal any attic penetrations
  • Flashing and Fire Caulking around Chimney Chases
  • Installation of a Thermadome (an insulated air-sealed box to sit atop pull down stairs)

Insulation to prevent thermal bridging and heat transfer

  • Mass Save program pays 75% of the total cost, up to $2,000
  • If more than 50% of your attic is un-floored than it can be improved up to R-38 (recommended by DOE in Northern Climates) by adding up to 12” of Cellulose
  • If you have a floored attic, there are options to air seal through a combined air sealing and insulation treatment, although the incentives are the same as insulation. (Dense-pack insulation)


  • Mass Save program pays 75% of the total cost, up to $2,000 as part of insulation services
  • Through ventilation, heat that accumulates in the attic is purged as cooler air enters through intake vents placed either on the soffits or low on the roof, and then pushes warmer air out through vents higher on the roof or along the ridge line

How to get started

The ultimate goal of the air sealing and insulation treatment is to prevent conditioned air – that you paid to heat to stay warm – from escaping from the living space and traveling into the attic, where it melts snow on the roof and creates ice dams.  In addition to preventing ice damming, weatherization is an effective way to lower your utility costs, increase comfort, and reduce your home’s carbon impact.

Sign up on the Green Needham web site or call Next Step Living at 866.867.8729 now to schedule your no-cost Mass Save home energy assessment.

Preventing Ice Damming