Multiwire branch circuits, which are now permitted in the NEC, are the only way to wire a shop, IMO. I have 2-gang duplex outlet boxes every 4-6 feet around my shop, each with 2x 120V outlets and 2x 240V outlets, all 20A. This makes it very convenient to plug in any machine up to 2-3 hp, along with any other corded tool, vacuum, etc. Each floor is broken into a few individual circuits, but all as multiwire branch, which saves a ton of copper.
The other must-haves here are heating
and air-conditioning. That shop is my solace, my happy place, on every 90F+ humid July or August afternoon, as well as every rainy April or November day. I schedule indoor vs. outdoor work according to the weather, so it's often "bad weather" when I'm working in the shop. I went with a Mitsubishi mini split system for this shop, with multiple indoor units sharing a single larger outdoor unit.
Agreed on what others have already said with painted OSB vs. drywall. OSB
painted a light color wins every time, for durability in a shop. On the painting, I moved into my prior shop (1998) before taking time to paint he OSB, and then it became impossible or impractical to do it later. For the most recent shop build, I was smart enough to realize that it'd never get done if I didn't just bite the bullet and paint everything before moving in. It makes an enormous difference in lighting and visibility, the older unpainted shop was always too dark to see and work on things, no matter how many shop lights I hung.
Another thing worth noting is high ceilings. I was working within an existing shell, adding a second floor to an existing roof line, so I had constraints. I chose to make the first floor ceiling higher, at the expense of second floor ceiling height, and glad I did it. If you work with wood, having the ability to turn sheets of plywood over end to end or corner to corner without hitting the ceiling is a convenience I always appreciate, as my prior shop had a ceiling low enough that this was a problem.
Hard air lines in ceiling of first floor, at full compressor pressure, distributed to separate regulators and separators on each floor. See recent thread on compressor air quality. No need to have hoses strewn all over the floor, esp. if you're parking tractors, vehicles, and implements in the shop.
I like the prior mention of a solenoid valve tied to the lighting circuit, to close off the compressor to potential line failures, although my only "compressor running all weekend" scenario has been due to a failed pressure-relief valve on the compressor's pressure switch assembly, and the valve on compressor outlet would not have prevented that. So in place of the valve, or perhaps in addition to it, a contactor with a 120VAC coil tied into the lighting circuit might be a better path to achieve the same. (edit: I see
@Runner just posted his electrical disconnect next to the light switch, even simpler/better.)
I've been researching closed cell spray foam, and it isn't as flammable as I had thought, and does very well at sealing. Apparently there is an Intumescent paint that reduces the spread of flames.
My shop is retrofitted into a 1770's (perhaps older) carriage barn, 2 story timber frame construction, which I framed in with 2x4 studded walls and OSB for wall board. I had the whole thing, including vaulted roof, spray foamed. If it weren't for the overhead doors, I'm convinced the rest of the building is tight enough that your ears would pop every time someone slammed a door.
Anyway, I was running copper air lines recently, and had to sweat a few joints right up against that spray foam, so I texted the insulation contractor to ask about its flammability. He claimed it was self-extinguishing, and I later proved he was correct in that assertion, it just burns out after a few seconds if you manage to light it. It's also pretty hard to light, in the first place. The wood from which the building is constructed is the much greater danger, than that foam.
