- Q. I have a job with a ridge beam built-up out of four pieces of LVL. Is there a ridge vent available that will span the wide opening this requires in the roof?
A.Henri de Marne responds: You could use a system I devised years ago before the advent of variable pitch ridge vents, a design which Air Vent Inc. (800/247-8368) borrowed and illustrates in their product literature for using utility vent on steep roofs.
You have the choice of setting the top of the rafters up 1 inch above the top of the LVL so as to allow an air space or of leaving the rafter tops flush with the top of the LVL and simply carrying the plywood to the ridge, where the two sides will butt (for extra support you can add triangular blocks on top of the ridge beam). If you choose the second option, cut a 1-inch-wide ventilation slot at the appropriate spot on each side of the ridge (see illustrations).
The ridge vent is composed of sections of Air Vent’s Utility Vent (it comes in 8-foot lengths, four to a package, with connector pieces and filter material) installed on each side of a site-built mini-roof. We found it easiest to build this mini-roof in 8-foot sections on the ground, attaching 1/2-inch plywood to 2x2s 24 inches on-center. After nailing the mini-roof to the ridge, we installed the vent strips over the plywood, and covered the whole thing with 15-lb. felt and roof shingles.
We used this system on my own house in 1979 and on a number of other jobs before adjustable-pitch vents became common. It is still one of my favorites because it is externally baffled and is as strong as the roof itself.
Henri de Marne, of Waitsfield, Vt., consults on building technology and is a contributing editor of the Journal of Light Construction.