In Vancouver you get three types of roofs. The first is the heritage home where the eave of the roof is probably twenty feet from the floor. The pitch of the roof is probably a 12/12 with three layers. The first layer is cedar and the two above are asphalt. Now day building code requires all roofing to come off before  a new roof is placed on. Plywood is essential and an increase of ventilation. Most of the heritage homes in Vancouver do not have soffit vents so having them installed is crucial.