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How to avoid same problems next year

The winter of 2011 has provided the Northwest Corner with some truly stunning displays of icicles. Drive (or take a slippery walk) down any local street, and you will be struck by the prevalence of huge icicles and ice dams on the eaves of many homes, both old and new.

Beautiful as they may be, these ice formations are the symptoms of some serious outflows of energy from within the structures they adorn.

The ice buildup, commonly referred to as an “ice dam,” is typically created when heat leaks through a snow-covered roof.

The escaping heat melts the underside of the snow layer, causing water to run down to the eaves. The eave portion of a roof, however, extends beyond the volume of the building it shelters, and so is not warmed by the escaping heat. Thus the snowmelt refreezes before it is able to find its way off the roof, transforming into ice on the eaves, in gutters and in the form of icicles, and eventually creating a dam.

The appropriately named dam then blocks any subsequent snowmelt-water from running beyond the dam, and forces the water up and under the shingles and into the interior of the house.

Soon the presence of leaks is discovered in the form of wet spots on ceilings and walls and around windows. Wires may also short out and wood floors warp.

Less immediately apparent is the damage the water can do to the wood structural members, where excessive moisture leads to mildew, mold and wood rot.

While the many recent efforts to clear roofs of ice and snow may resolve the ice dam problems temporarily (and also prevent some potential structural failures due to the weight of this winter’s snowfall), the only way to permanently prevent the dams from forming is to air-seal and insulate, especially at the attic or roof level, where a majority of heat escapes.

If everyone effectively air-sealed and insulated their houses, energy would be conserved, people wouldn’t risk their lives hacking ice off their roofs, and homes would be protected from the potential damage that the dams create.

Air-sealing is nothing more than sealing any leaks that are present in a home’s air barrier.

Basically, you want an air barrier that works like a zipper-topped storage bag, sealing in conditioned (i.e. heated or cooled) indoor air and sealing out unconditioned outdoor air when it is closed.

Adding insulation alone without air-sealing first would be akin to filling your oil tank when you know it has a hole in it.

Checking for leaks

The best way to find the leaks in an air barrier is to have an experienced professional use a piece of equipment known as a “blower door,” which is an adjustable frame and membrane panel with a big fan stuck in it.

The blower door is placed in an exterior doorway of a house with all other exterior doors, windows and storm windows closed tightly. The fan portion of the door is then turned on, blowing air to the outdoors and thereby creating negative pressure inside the house and pulling outdoor air through any existing cracks and holes, thus making them easy to locate.

The areas where cracks and/or holes are found are then sealed using some basic materials such as caulk, spray foam and rigid foam.
Once a home has been thoroughly air-sealed, there are several means and methods of adding insulation.

The best strategy for each unique situation needs to be determined based on issues that include energy performance, sustainability, cost and payback time, and disturbance to the functioning of the home as a household.

There is a federal energy efficiency tax credit available for air-sealing and insulation projects (10 percent of the cost up to a maximum credit amount of $500).

For possible assistance in financing air-sealing and insulation work of an “emergency” nature, it would be worth contacting the Connecticut Housing Investment Fund (chif.org).

At least it isn’t melting

As a last resort, if air-sealing has been carried out but insulation levels cannot be increased enough to eliminate ice dams, a roof-venting system can be installed. This keeps cold outside air circulating between the roof and the insulation so that the roof stays cold and melting doesn’t occur.

It also means that heat is likely being transferred to the ventilation air and exhausted through the vents. Heat may still be escaping; it’s just not melting the roof snow.

Abeth Slotnick is an architect who lives in Salisbury.

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