Roof vents

Published on May 7th, 2013 | by Henri

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Ventilation problems and ice dams after new roof installation

Q.    We own a two-story colonial built in the late seventies. The garage is attached to the main section of the house. A new roof was installed four years ago along with roof vents. The original roof was white while the new one is a grey/green color.

Since the new roof was installed the garage is excessively hot in the summer and likewise cold in the winter. The family room, which is adjoining the garage, is also affected in the same manner. The garage is not insulated except for the area surrounding the family room.

When we tried to contact the roofer, we found out they had gone out of business. We turned to a local contractor and he suggested that since the problem wasn’t there before the new roof was installed maybe the area of the ridge vent was too much and he covered the opening from the inside with some light insulation. This did help the situation slightly. The section of the house under the main roof is not affected in any way.

Last year, for the first time in 30 years, we had a problem with an ice dam forming on the back roof over the family room. Any ideas you may have concerning this problem and a possible repair would be greatly appreciated.

A.    The previous white roof reflected the sun’s heat and kept the garage cooler. The new, darker roof lets a lot of the sun’s heat penetrate. I doubt that the new roof is affecting the temperature of the garage in winter; if there is a marked difference, it is for another reason such as increased ventilation.

You mention new roof vents but you didn’t say what they are so I can’t tell if they are part of the problem. Reducing the ventilation of the ridge vent as the contractor did is not the best idea; what you want in summer is more ventilation to exhaust the build-up of heat but, to be effective, there must be equal or greater ventilation intake from the soffits with no interference from any gable vents.

The fact that the section of the house under the main roof is not affected tells me that you have ample insulation of the ceiling in that part of the house. This slows down the transfer of heat from the attic to the living quarters below during the day. Later the attic cools down as the sun goes down and the day’s temperature also drops.

As for the new ice dam on the back of the family room, ice dams form when the roof’s snow cover melts from below because the attic’s temperature is above freezing. As the ensuing water reaches a cold part of the roof, it freezes and the ice dam builds up as further melting takes place. If this never occurred before, were any changes made to cause it to happen now? Was a skylight installed? Were heat producing can lights added in the family room? What else was done?

As for remedies, the easiest way to cool the garage down is to increase ventilation so the air is exhausting faster as it gets warmer. Another solution is to staple special aluminum foil under the garage’s rafters to reflect the heat back out through the roof.

I would also suggest that you remove the insulation the contractor stuffed in the ridge vent.

To eliminate the ice dam, check for any sources of heat that were not there before and deal with them either by removing them or taking measures to control them effectively (obviously nothing can be done if you have a skylight). Add insulation in the ceiling of the family room and increase the attic’s ventilation.

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