Originally Posted by roofnron
Agreed with WoW, there are directions on the ridge vents that tell you how much to cut. It is a little different based on whether or not you have a ridge beam or trusses.
A house I am working on this past week the carpenter but the ridge vent 2 inches on either side of the ridge. Now the ridge don't look like a ridge, looks like a min-flat section up there. Cutting too much can also affect the weather-tightness.
I am using a ridge beam (offset a bit), so I get 1.5" on either side of the ridge board, but 3" at the bottom of each rafter cavity, continuous up to very near the top. I just don't see how 3" of space (on each side) can vent out completely through a 1.5" (per side) ridge vent. Still, the Ontario Building Code requires a minimum 2.5", and I am creating the 3" space in each rafter cavity, then furring the 2 X 6 rafters out 3" (with n=2 2 X 2's) so I still have 5.5" left to fill with R22 Roxul. (The I will apply 4' x 8' sheets of R13 foil-covered Thermax high-density foam overtop, for a total R value of R35.)