My wife & I just bought, in Connecticut, a house (Cape-style, built in 1951) with an asphalt shingle roof that is about halfway through its life and needs some relatively straightforward minor repair and maintenance, which we will of course have done. A semi-finished room had been created out of 3/4 of the attic, and we definitely want to finish the room and have it fully habitable. But, although there's insulation blown in beneath the finished portion of the attic and a forced air duct up to it, there is NO insulation under the roof (behind and above the drywall shell of the room created within the attic). The room can only be habitable if insulation is installed; otherwise heating or cooling would prove incredibly costly and wasteful. However, before we move to install insulation and properly renovate, the issue of the roof's ventilation needs to be resolved.
The roof, which is not steeply pitched, is unventilated, except by very small gable vents at either end of the attic, and windows at either end of the attic below them. (One window — in the smaller, unconditioned portion of the attic that has become a closed-off storage closet — has a large fan). There is no ridge vent and there are no fascia, hence no soffits. The lower edges of the roof [which lies on tongue and groove boards that are in good shape, not plywood] simply end at the vertical walls of the house, where the gutter is located.
After speaking with several roofers, there seem to be 3 options for the roof (which have different costs and very different insulation implications):
One roofer suggests adding a ridge vent and a solar powered fan to keep the roof ventilated. If this is adequate ventilation, presumably then some form of insulation batts could be installed while leaving space for air flow. (My concern is that this option, without any soffit vents, still may not set up needed intake of cooler air from below.)
A different contractor has proposed adding a ridge vent AND extending the lower edge of the roof on all sides to allow the creation of fascia and installation of soffit vents leading to the ridge vent. This would definitely work for ventilation of the roof, and presumably conventional insulation could be installed over the vents, while preserving air flow. But I presume the roofing work would likely be extremely expensive — it means rebuilding the roof at top and bottom. (We're still waiting for the written estimate from this contractor.).
A colleague who had a similar situation out at his last home in Seattle suggests keeping the roof in its current configuration (with suitable repair of shingles & flashing), and then using closed cell spray foam insulation underneath it. (I have been told by a friend who is a carpenter that spray foam insulation right under the roof would eliminate the need for ventilating the roof.) Though I know that the closed cell spray foam is considerably more costly than other insulation, this option might be cost effective in view of the costs of alternative number 2.
I would love to hear any informed opinion about these options, especially from someone who is not trying to sell us something. If we put in a ridge vent, can one solar attic fan (or even two) provide movement of enough air (especially cool air in the winter) to prevent mold or rot beneath the roof and avoid ice dams? IF spray foam insulation under the roof proves a cost-effective alternative to adding a ridge vent + extending the roof and installing fascia and soffit vents (plus, of course, conventional insulation), is it reasonable to leave the roof's current configuration unchanged (except for closing off the small gable-type vent) and apply the spray foam? Beyond cost, is this option likely to cause roofing problems (now or in the future)? Do we really have no option other than creating a ridge vent + fascia+soffit vents?