Insulating advice for an old drafty one

[dickfink]

Been reading here a bit and ya’ll seem like a smart and knowledgeable group! I’m a decent woodworker (more furniture than home building) but could use some input on insulation and AC Stuff.

I have a long and narrow garage — probably built around 1925 or so. The front 2/3 is storage + workshop, and I’m slowly turning the back third (about 11.5x14) into a craft room / part-time office. I’m in the LA area so fairly dry and warm in the summers. No freezing temps. Right now the structure is completely uninsulated so it is pretty miserable in the summers.

Long term we might turn the whole thing into a more proper back-house, but for now I’m looking for a bit of a temporary improvement and figured insulating the walls, adding (and insulating) a ceiling and sticking a mini-split in would help. I was thinking just un-faced fiberglass batting.

The thing is…the back 1/3 has a Dutch gable roof, with the gable end is a lattice. I think I should cover it (at least loosely) to prevent critters from getting in and nesting in the insulation — but there are no other true vents — although the roof to wall definitely isn‘t air tight.

And the “ceiling” joists are the original 2x4s…spanning 14 ft. It looks like there used to be some ceiling material on it, but I’m a bit concerned about it holding drywall up.

Attached is a photo of the space (it had some plywood sheets for earthquake/structural stability — I might keep those and I just put scraps in the other parts), the ceiling above it (showing the gable end) and the old ceiling material (in case anyone knows what it might be).

Also any input on order of operations? I figure 1. run electrical for HVAC 2. insulate 3. wall it in (ceiling first) 4. Paint 5. Install Mini-split.

Sorry for the ramble…

 

[AC-WC]

I'm not sure those are true ceiling joists and they may not hold up drywall and insulation. Are they 16" on center? If you can tell if your house has 2X4 joists then you're probably safe.
A potential is hanging white barn siding as the ceiling and blown in insulation.
It weighs less than drywall and already painted UNLESS you really wanted the smooth look of drywall.

You will need to use these regardless of type of insulation. There are different styles but most DIY places have them.

ADO Products Durovent® 22" x 48" Polystyrene Attic Vent Chute

The Durovent® attic ventilation system helps keep air flowing in your attic. The ventilation system can be cut to fit most joist spaces and provides you with an economical way to meet energy code requirements for attic air flow. Install the system between rafters to provide an air channel...

www.menards.com

Keeps the air flow from the wall/ceiling gap from being plugged up with the insulation. Recommended regardless of type of insulation. You need the airflow to vent out from the side up the rafter to your gable end.
It sounds like you're in So Cal so vapor barrier needs to be closest to the heat side. It does make a difference for your geographical heat zone. In my area we need it on the inside.
Your order of install is right on. Electrical is WAY easier with exposed studs.