We live in Thunder Bay, On. In 1992 we had new soffit installed. He put it over the old without enlarging the vents. We have had trouble with condensation in the front of the house ruining the plaster. We had it repaired by ice & water shield, applied to the roof and valley. The front soffit was removed to make larger vents, then reinstalled. They went up into the attic and put more vents in front, and also pulled the insulation away from the vents. We had no problems with condensation last winter. They told us we need more insulation to bring it up to R40.
Answer:
Your rule of thumb is going be to have 1 square foot of roof venting for every three hundred square feet of attic floor space. A baffled ridge vent will look after that and all the others can be removed. Along the bottom (soffit) you might look for daylight all the way along the lower edges of the roof. This system will give you far more than the recommended ventilation but remember, you cannot over ventilate an attic.
