This is my first post here. I was hoping to get some advice on the best way to vent the roof of a detached garage when I can’t install soffits on two sides of the structure.
I’m a homeowner in Portland, Oregon, and I’ve been building this garage/studio for the past few months. This is the first structure I’ve ever framed. Except for the concrete foundation I’ve done all the work myself (with the help of some friends along the way.) I’m at the point where I can roof the unit. If I’d gotten an earlier start and the weather was nicer I probably would have done it myself, but since the weather’s crappy we’re getting bids on having professionals do it.
Here’s a website with some progress photos:
Both the garage and studio will have cathedral ceilings. The roof is around 660 square feet and will have three self-flashing (deck mounted) Velux skylights. The rafters are 2x10’s and will have R-30 high density batt insulation, which will theoretically leave an inch at the top for air flow. My plans call for continuous ridge vents along the two ridges. The tricky part is getting some air flow up from the eaves. Because this unit was built one foot from our north and west property lines (after obtaining a variance from the city) we have to have one hour resistive fire walls on those two sides of the structure. This means a layer of 5/8 inch sheetrock on the exterior (to be covered with Tyvek and siding), no openings in those walls and no roof overhang. That means I can’t put soffits or vents in those walls, and I can’t have any opening in the roof within three feet of the property line.
The first roofer to come out suggested putting SmartVents along the lower edges of those roofs to bring in air. I did some research and that seems like a plausible approach, though his bid’s been the highest so far.
Another roofer, whom I liked and was closer to our budget, wasn’t familiar with SmartVent. He suggested standard square vents in every rafter bay, but that would look hideous. I talked to one of my city inspectors, and he was somewhat helpful, though he didn’t instill me with a ton of confidence since he had to keep putting me on hold to get my questions answered. He came back and said I could install a few standard static vents in some of the bays (no closer than 2 feet from the edge of the roof), then a drill 7/8" hole near the top edge of each rafter to allow air flow between the rafter bays. This seems plausible, though I’m not convinced that would allow enough air flow.
A third roofer came out, but when I asked him about using a SmartVent type system along the lower edge of the roof he said he didn’t like that approach because those kind of vents clog. I don’t know if he was referring to the SmartVent or the metal drip edge-type vent (which I couldn’t use here anyway because it’s too close to the property line.
As shown in my diagram, I will be able to install some typical soffits along the front part of the structure, though a skylight blocks two rafter bays on the studio (south) side.
So, any thoughts or suggestions? I can see that the issue of venting can generate a lot of controversy on these boards, and these firewall limitations are making things harder.