Just when you think you've seen it all...

recently bought a house, and excited to turn a 14'x20' garage into a shop. There's some funky stuff the previous owner did in regards to, well, everything! (wiring, framing, hanging doors, etc.).

there are new, 14' 2x8 joists (24" OC) that do not rest on top of either side stud wall. rather they are just screwed and nailed in to the 2x4 rafters of the hip roof. Essentially these ceiling joists are now rafter ties.

on to my question...I want to hang 1/2" drywall and add some insulation above. There won't be any additional storage weight in the new attic space. Is this acceptable? I'm not worried about meeting code, because there's so much stuff that isn't code in there and at the end of the day it will still be an unfinished garage space.

I don't really want to remove/replace the joists either. Are collar ties or some kind of metal hanger/tie sufficient to transfer the roof load? Can I just leave it as is?

not the best picture, but you can see the joist ends at the stud wall...

I'm not a builder.
But those seem like overkill as rafter ties, and they aren't collar ties.
14' span means a pretty small attic height, maybe 32"?
Beware of making a ceiling and blowing in insulation. You get into problems of no ventilation, a very hot space closed in, turning to sponge wood in 10 years, susceptible to fire, plus probably filled with critters and bugs, or rot from moisture getting in, all typical shed situations. Dead mice in the walls or ceiling, ugh.

If it were my shed and I planned to heat it, I would put up 2 x 8 x 1.5" foam insulation (nice and light and removable) right onto those existing ties, tape the seams, then cover with thin vinyl strapping. Might not be pretty, but I would want a shed that is easy to get to hidden spaces. You can even put some of it up 'wrong' across the ties, so that there is only a little bit left over.

And 2 small square vents on the roof, or a ridge vent.

Move the wiring, fill with batts, staple on a vapor barrier, add drywall or white 4 x 8 vinyl panels.
Easy access would be key to me.

Probably because they didn't want to buy 16' joists and then cut off almost 2 ft. of them. They only hold themselves up but do help to keep the walls from spreading. I'd use inexpensive floor underlay for the ceiling, not much more than drywall and a lot easier to hang. For extra support, if you think you need it, drop a 1x4 from the ridge to the 2x8. Looks like it might have had a metal roof that was removed and decked with plywood.

@joypulv thanks. It's a small attic but the garage won't be heated (well, maybe a space heater a few days in the winter), was planning on adding two vents anyway

If the garage won't be heated, I'd think twice about any insulation at all. You are just asking for rot, mold, bugs, mice and taking 30 years off the life of the wood. Even occasional heat, I wouldn't do it at all. Even with ventilated roof and vapor barriers. Trouble, trouble!