Sorry, I should have specified my location -- we are just outside of DC, so we typically have hot, humid summers and fairly cold winters. We don't get the extremes of some areas of the country though. I'm encouraged by the comments from both of you. Worthy, thanks for the article. I understood most of it. I think we have done a pretty good job of separating the conditioned living spaces from the unconditioned attic so the underside of the roof stays cool in winter. When it snows, the snow stays on our roof much longer than it does on neighbors' roofs (I always thought this was a good sign that our insulation was working) and we've never experienced any ice dams. We never see signs of moisture or mold in the attic or on things stored there. It does get very hot in the summer. As you climb the stairs from the second floor to the attic, you can feel the temps rise. Our basement used to be very damp, but since we had closed cell insulation sprayed on the rubble stone walls, it feels and smells much drier...if we're keeping the moisture out of the house, the attic should be drier as well, yes? Worthy, I'm thinking and hoping that you are right and that if it has been fine for 108 years and we've improved the envelope, we should be fine. Thanks so much for weighing in.

First, you need to separate "attic ventilation" from your desire to "cool the attic air", then understand the purpose of each and then understand their effect on the roofing shingles. Attic ventilation is for the purpose of allowing moisture to escape from the attic space with an area ratio of 1:300 which involves very little air movement. Studies have shown that this level of ventilation has little if any meaningful effect on the temperature of the attic air or the temperature of asphalt shingles. But it does allow excess water vapor to escape and insulation to dry out if there is a leak or if water vapor has entered from bathrooms or rain and/or snow blowing through oversized vents. Don't try to make this system do more than that. If you want to cool the air in attic space you will need to move a great deal more air but there are two problems with doing that. First, that amount of air may draw moist air into the attic. Second, the major source of heat in an attic is the radiant energy (invisible infra red light) that is emitted from the hot back side of the roof sheathing. As radiant energy travels through air it does not raise the temperature of the air but when the radiant energy strikes the attic floor, it heats the floor and the floor then heats the attic air. Exchanging this hot air with less hot outside air by fan might lower the temperature of the attic air but it will do little to cool the hot attic floor and roof sheathing. Adding a radiant barrier under the rafters or on the attic floor will help to reduce the heat reaching the interior of the house by directing it back up toward the roof sheathing but that will not help cool the roofing shingles. Roofing shingles directly exposed to the sun are already as hot as they're going to get and there is little you can do inside the house that will reduce the shingle temperature by more than a degree or two. If you want to keep the hot attic air from increasing the cost of cooling the house add more insulation and move any AC ducting out of the attic. I prefer to include the attic space in the conditioned portion of the house by insulating between the rafters and installing an air vent path between the insulation and the roof sheathing. Aluminum foil on the back of the sheathing will help to reduce the heat that reaches the attic but this design will not reduce the temperature of the shingles. More effective ways to increase the life of your asphalt shingles are to use a lighter shingle color, trees, etc. for shading, face the smaller side of the house toward the south, or move farther north.

A gable fan would be hard to install because the gables are up there behind the ceiling and walls. The only access to the eaves are the kneewall doors and there isn't much space behind them. We'd have to cut the ceiling to get up there to the gables. The extra roof is an interesting idea. Would the sleepers run up and down the roof and create the pathway for the air? Or would they go across the roof? If they go across, wouldn't they then block the air pathways? Would the extra weight of another roof be a possible problem? How could I tell if the structure could handle sleepers and an extra roof? The present roof sheating is 1x4 boards, not plywood. I'm told there are some soft spots and some of the sheating is likely going to have to be replaced. There was a leaking problem in 1998 and roof repairs were done then, but I don't think they did anything to the sheating then. Can baffles be put in from on top the roof after the top is cut off for the ridge vent? Could they slide in from there or do they tear up too easily? Are baffles ever made of anything besides foam? The house has been there 56 years and the present roof has lasted 29, all without roof ventilation except for the gable vents, so I'm wondering why a new roof would start to have problems because of lack of ventilation. It's a pretty steep roof, if that makes any difference in this issue. I'm going to use a light-colored shingle. There are mature shade trees in the yard, and one in particular shades it from the west. Virginia is hot in the summer, but in the winter it seldom gets below 20.

The air vent is used to cool the roof during the hotter months so cooler air flows up thru the attic and drops the temperature and the reverse during the winter. This is a good solution.