I live in west Michigan in a home built in the early 1900s that has a walk-up attic. There are no soffit vents, but there are 3-5 "pop vents" installed in the roof. The attic has five separate gables, each with double-hung windows that are glass on the top and vented on the bottom. The house has no insulation in the outside walls, though there is some insulation between the first and second floors and the second floor and attic. Would it be a better idea to block some or all of these vents instead of letting all the cold air inside? I understand the need to vent the roof to try and minimize the build-up of ice, but the amount of venting I have seems extreme. Does anyone have any good suggestions?