Insulation

Published on November 28th, 2013 | by Henri

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Power ventilators not a solution to ice buildup

Q.    I need some advice regarding attic ventilation. I live in a large 12-year-old-home that was built with steep hip roofs — totally inappropriate for New England winters as the amount of ridge vent available is inadequate for proper winter ventilation.

This, in addition to a south-side cathedral ceiling, results in large amounts of ice build-up. I’ve had leaks, rot and huge icicles. Over the 10 years I’ve owned the home I’ve used heat tapes, redone portions of the roofing materials to include storm shielding (as this was not used originally), and I still am not satisfied that I’ve addressed the problem properly.

I believe I have to force air through the attic to achieve the least amount of melt-off. So I have come to the conclusion that I should install power roof ventilators. Do you have any recommendations?

A.    I would not recommend power ventilators, as they are likely to make matters worse by drawing make-up air from the living quarters. Ventilation is an important part of roof health but there are other ways to prevent the problems you are experiencing if ventilation cannot be provided.

The most important thing to do is to make sure there are no convective paths from the living parts of the house into the attic. Be very careful in that examination. Years ago, I worked on a case where extensive rot of the rafters had occurred in an unventilated attic from a drywall tape that had separated at the peak of a cathedral ceiling; warm, moist air entered the rafter spaces and wreaked havoc.

There should be no recessed light fixtures, no cracks anywhere. Seal all wall and ceiling electrical boxes with closed-cell gaskets throughout the house. If there is a scuttle hole to the attic, make sure it is weatherstripped with closed-cell tape. If there is a folding attic stairway, install a specially-made insulated cover for it.

Make sure that all bathroom and kitchen fans are vented to the outside and not into the attic. Same goes for the dryer vent.

Once you have made sure that there cannot be any convection into the attic, look into adding insulation in the attic over flat ceilings. Several inches of cellulose blown in would be ideal — don’t hesitate to have two feet of insulation.

The cathedral ceiling is another matter. The best way to deal with it is to fasten 2-inch thick extruded polystyrene or polyisocyanurate rigid insulation to the ceiling (tape all the joints) and cover it with new drywall.

These steps should reduce, and perhaps even eliminate, the melting of the snow cover from heat loss.

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