Backside venting for wood shingle roofs?
I’m an architect specializing in historic preservation projets. We’re going to be re-roofing some wood shingle roofs on some historic barns and outbuildings in Long Beach, CA. The buildings need seismic upgrading, so we’re also considering adding plywood sheathing to the roof on top of the existing skip sheathing.
We’re concerned about the loss of ventilation to the backside of the singles. Conventional wisdom is that this shortens the shingle life. Do you see that in the field? How much shorter is shingle life on a solid substrate?
If we want to ventilate the backside of the singles, any tips on how to efficiently do this on top of plywood sheathing? Putting skip sheathing nailer boards on top of the plywood only creates a sealed air space below the shingles. A double layer of perpendicular 1x skip sheathing (boards going up the roof at 16″ o.c. under boards across the roof at the normal skip sheathing spacing) would create a place where air could flow, but we’d need to add eave and ridge vents to make that actually work. Of course we’re not real anxious to change the eave and ridge detailing on a historic property.
Any suggestions and input would be greately appreciated.