Q: Even though we have done a good deal of work to increase energy efficiency in our 1960 split-level home, we are having a difficult time keeping the warm air inside the house during winter months.
We have replaced all the windows with energy-efficient windows. We have R-19 insulation in the attic. Last year we had a new furnace installed. Most of the heating ducts are in the crawlspace under the house or the garage. Some are in the walls to reach certain rooms since it is a split level. Our house is very cozy and we have had relatively low energy bills in the winter.
But this past October we had a new asphalt shingle roof put on. The house was already equipped with soffit vents and the roofing contractor added eight passive vents on the roof. Now, all the cold air coming into the attic means our house maintains the furnace heat for only a short time.
What can we do to keep the warmth in the house during the winter? Should we add more insulation in the attic? Or should we cover the roof vents in the winter? Maybe we should just wear down vests?
A: Attic vents in some shape or form have been a standard feature in home construction for many years. Drive down any street of older homes and you’re sure to see gable vents staring at you from the apex of walls meeting pitched roofs.
Roof vents installed near a roof’s ridge and continuous ridge vents are relative newcomers to the world of attic ventilation. Whatever type of roof ventilation exists in a home, the purpose is the same — to provide airflow through the attic space.
Air movement inhibits the formation of condensation by equalizing the attic air temperature with the outside air temperature. This also means that warm air is removed from the attic. The unintended consequence of your recently installed roof vents is that your house got colder. In the winter months, warm attic air is vented to the outside through the ridge vents and is replaced by colder outside air sucked in through the soffit vents. In essence there is a mini jet stream in the attic. The system is behaving as designed. We think the problem lies with warm interior air migrating to the attic and getting caught in the jet stream. This makes your new heater work overtime, increases energy costs and makes your home uncomfortably cold.
While we have nothing against down vests, we do think of them as outdoor, rather than indoor, wear. And don’t cover the vents — they’re doing the job efficiently. But definitely add more insulation.
The standard these days for attic insulation is R-38. That translates into a full 12-inch thickness of blown-in or batt insulation. But beefing up the insulation alone may not solve the problem.
Channel the soffit air and button up the cold spots before the new insulation goes down. The air entering the soffit vents must be directed to the attic space, and the interior walls and ceilings must be fully separated by insulation from the attic air.
Possible areas where interior air could leak into the attic are around pipes, voids in the insulation, and at the soffits where the vents should be unobstructed and the interior spaces should be fully insulated.
Before installing the new insulation, make sure you seal penetrations from the interior space to the attic. This includes holes for electrical wires and plumbing pipes. Seal them with expanding foam insulation available in an aerosol can. "Great Stuff" is a brand name that comes to mind.
Isolate the air moving through the soffit vents into the attic by fabricating a chimney from cardboard at the soffit in each rafter bay. On the bottom edge of each rafter, nail or staple an 18-inch piece of cardboard so that it covers the entire width of the bay and extends to the top plate of the interior wall. Make sure it does not obstruct the soffit vent. Install the insulation tight against the cardboard.
The result will be a fully insulated interior ceiling and a chimney directing the outside air from the soffit vent into the attic. Done carefully, this process should eliminate cold spots where the attic meets the interior and improve the energy efficiency and comfort of your home.
This should make wearing down vests inside a matter of choice and not necessity.
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