Insulation, Radiant and Vapor Barriers - Insulating Unsheathed Garage Walls

I'm helping my son convert an old garage into a sculptor's studio. He plans to instlall a propane heater with external combustion air intake and insulate the ceiling and exterior walls. The structure was originally built without sheathing on the exterior walls--just siding nailed to the studs. How can I insulate these properly since there's no Tyvek on the exterior surface? I see no evidence of water damage to the siding, but should I be concerned about moisture damaging the insulation?

Also, some of the studs are on 12" centers and some (in the ceiling) may be 20". I guess I just need to cut, staple and tape pieces in sized so as not to compress, right?

As always, thanks.

angus

Fiberglass is only affective when you airseal along with it...air can pass right through it...seriously weakening its thermal barrier properties. tyvek...for example would be a wise descision to apply before hand....even though you haven't seen moisture...personally , I wouldn't take the chance. Also..propane heaters should be used in well ventilated areas...so keep that in mind...and install a Carbon Monoxide detector in the studio...good luck!

What type of siding is applied? Horizontal lap, I would be concerned about walls racking. Are let-in 2x4 blocks nailed on the diagonal at each corner? Or 1x4? Is the garage detached ( stand alone)? If not, you should fix the shear stability first, or at least befor wall board. Be safe, GBR

What type of siding is applied? Horizontal lap, I would be concerned about walls racking. Are let-in 2x4 blocks nailed on the diagonal at each corner? Or 1x4? Is the garage detached ( stand alone)? If not, you should fix the shear stability first, or at least befor wall board. Be safe, GBR

It's horizontal lap siding. There are diagonal 2 X 4s on the corners and it is detached. The original garage has been there since the mid-40s and they apparently added two bays on one side of it. It seems very stable.

Thanks.

Fiberglass is only affective when you airseal along with it...air can pass right through it...seriously weakening its thermal barrier properties. tyvek...for example would be a wise descision to apply before hand....even though you haven't seen moisture...personally , I wouldn't take the chance. Also..propane heaters should be used in well ventilated areas...so keep that in mind...and install a Carbon Monoxide detector in the studio...good luck!

Thanks for the reply. This is a 1940-s era garage. How would I apply Tyvek to the inside of an existing structure that has siding but no sheathing? Would I run an unbroken roll across the studs and staple it deep in the cavities, or would I cut a piece for each cavity? Can Tyvek be used at all once you've installed siding?

Secondly, do I even need Tyvek if I use faced insulation with the moisture barrier on the inside? Actually, I assumed that this is how I'd handle this, but with the non-faced side of the rolled insuation touching the unsheathed siding, it got me wondering about moisture issues.

Thanks again.

Well it depends how much money you want to spend. Spray foam would take care of the moisture barrier and insulation at the same time. Providing there are no big gaps in the siding that the foam could push through to the outside.
Another option would be to cut tar paper or roofing paper to fit between the studs with enough extra on the sides to be able to staple it to the studs. Then if water did get by the siding it would be stopped by the tar paper before it gets the insulation wet. Just be sure the water cannot pool inside the stud cavity at the bottom and get wicked up by the insulation.
Check prices you may be able to get it sprayed for just a little more than the materials and labor of other options. Don't forget to factor in the added benifit of knowing the insulation will not get wet and mold.