Dan, the garage ceiling is the underside of the roof; IOW it's completely unfinished. I don't want to put in a ceiling under the roof joists because the storage space above them is too valuable, especially for long lumber. (Your question about the gable makes me think that I might indeed need a couple of doors in them. Thanks!) I might someday insulate the underside of the roof.
But to answer your question in more detail than you may have time to read, there's solid blocking above the top plate only between every other pair of rafters. The alternate pairs have nothing at all, not even screening.
So while I can put in screening for pest control, I need the little swinging doors for humidity control and ventilation. (We've never had a squirrel get in, although we did have one set up housekeeping above our bedroom, but we do have a rodent problem. Last time it was a wood rat--a kind of pack rat--and for a couple of years after we got rid of it I kept finding caches of small L-screws up in the rafters.)
As I said, we get a lot of rain, and rust is definitely a problem in the garage. My second year up here was an El Niño year that delivered over 100 inches, and in 1982, following 2 months of record rainfall and a 24-hour total of around 12 inches, the steep mountainside above Love Creek in a town just down the road basically melted, burying 9 houses and 10 people under 600,000 cubic yards of mud: 80,000 dump truck loads. None of the bodies could be recovered and that part of Love Creek Road now literally runs over a cemetery.
I can't just block off the openings permanently because I can't afford air conditioning, so I need the doors openable to get the most ventilation possible in summer, which is very dry and often hits triple digits. In fact, the year before last, during a scorching heat wave, Boulder Creek was the hottest place in the U.S., even hotter than Death Valley. Fortunately, since we're in a Mediterranean climate, all but a tiny fraction of our rainfall arrives between November and April, with freezing temperatures in January and February, so I'll only need to open or close the doors twice a year.
Anyway, thanks for your welcome and your questions, which not only gave me an idea for lumber storage, but also taught me the proper terminology for some of the components of a roof and the part of the wall it rests on. That sort of knowledge makes it a lot easier to communicate with a contractor; much more so that pointing, handwaving, and using words like "thingumbobby!"
Last edited by davetrow; 03-23-2019 at 07:20 AM.