We have a 1924 duplex in Washington, D.C. and we are in the process of renovating our attic. We are concerned about proper ventilation and insulation between the area we want to use as living space and the mansard roof which is mostly flat, but peaks towards the front and side.
Do we need to create an air space between any insulation and the roof? or can we simply put in insulation with vapor barrier in the ceiling, and not worry about ventilating behind the insulation?
If we do need to ventilate, where does the air go? We don't have a true peak where we could let air escape that way. We could create a space that connects to the unused attic space which is at the flattest part of the roof, but since heat rises, would that merely push the air up to the highest point with no escape? There are soffits on the front and side of the house which we could vent, but again, the air could only go in one direction, up, to the peaked part with no escape.
If we have an attic fan in the unused portion will that be enough to draw heat out?
Any advice is greatly appreciated.