Ridge vent not adequate

check

I am leaving a 3" space umder the roof in each rafter cavity, but the ridge vent only provides 1.5" at the top. Is this adequate?

Windows on Wash

Always better to err on the side of more intake than exhaust. Most soffits and vents don't flow what you think and you need to look up the net free area of the vents in question but you are probably just fine.

__________________

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.

check

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.)