What is the best way to insulate the floor of an attic if the house does not have soffit vents – or any soffits at all? There is a ridge vent and two gable vents for ventilation. Do I need to install special soffit-less vents, or can I insulate right into the corners of the attic, right up to the roofing boards? I live in New England and am concerned with ice dams.
There's a type of vent called an edge vent, specifically designed for this purpose. Edge vents basically extend the roof edge by a few inches so you can pick up space for soffit insulation. A ridge vent is good, but is only half the equation.
Unfortunately for your situation, edge vents are best installed as part of a larger roofing project. The roof basically starts at the edge of an edge vent, so it's difficult to add them after the fact.