Garage insulation and polyiso boards?

[bud16415]

Given the construction method of the wall and that you like the idea of foam and it is DIY so the time spent on the project isn’t a factor.


I would do the whole job with 3” thick foam. I got a load of free used foam when I did my garage workshop and it was old DIY construction with stud bays of all different widths. I cut and fit the foam for each opening sometimes piecing it in. I got it fairly tight and when done I used great stuff spray foam on any cracks and joints. I cut mine with a sawzall. But any saw with a long blade will cut it like butter. There is no waste as you can piece it in to use it all up.


Then inside drywall or peg board or even plywood and paint.

 

[Sparky617]

If you aren't heating and cooling your garage your ambient humidity (low in most of California to begin with) will be the same as the outside. A vapor barrier on the inside isn't going to do anything. The tar paper on the outside is secondary protection for rainwater that gets past the siding. Keeping a proper coat of paint on and sealing seams in the siding and around penetrations along with gravity (water flows downhill) will keep the sheathing dry.

 

[fastsvo]

Out of curiosity, how about if I do one day to decide to cool/heat the garage. What would I do differently here? Our climate here is definitely on the dry side.

 

[bud16415]

@ Sparky617


I don’t think he has sheathing that’s the reason for all the cross pieces for someplace to nail the board and batten siding.


No one around here would build a wall that way anymore.


@fastsov


If you did the solid foam I don’t think you would do anything different if you added heat or AC. It would be the same system as if you had it spray foamed just not as expensive. In a way you will be conditioning the space if you leave a window open over night the area will be cool in the morning. Close the window and trap the cold inside against the heat of the day. Or if you are using the space as a workshop like I do a small window AC unit will keep it cool if insulated fully. We get temps as low as –30f here in the winter. I use the workshop with a small propane furnace that has two inferred burners. I fire it and go back in the house for an hour in the morning and it is not to bad when I go back out. I also have a window AC but it doesn’t get used too much here. I was worried about condensation and my tools but so far it hasn’t been a issue.

 

[MrMiz]

depending on what's going to be put on the wall I would do full sheets of Polyiso with foil side out then cover with drywall or plyboard, and appropriate length screws. If your going to be hanging anything really heavy on the walls you might need to support the plyboard a little more, but then if you ever get around to the siding, fix the exterior house wrap then. It's probably been fine that way for years. You don't have to fix it this project. Your doing and interior project this time and in my mind that means an exterior fix is a different project for when you have time or money. While I think everybody can go on and on in the debate about exterior house wraps here is what I know. In a "dry" climate exterior wrap (that doesn't have rain or plumbing leaks already) isn't mandatory. I'm in a dry climate, and I have 2 houses over 100 years old that don't have any house wrap or insulation in them and they are in great shape with no decay. If you were in a humid/rainy climate then that is a totally different animal. I think sometimes people forget building for the climate/zone/location your in can significantly alter the things you do.
In your case I'm sticking with address the efficiency and finishes interior and don't sweat the exterior project till its time. My 2 cents.

 

[Snoonyb]

Kinda amaze how you guys deal with the heat! I'm curious on what type of wall you have in your garage? Is it concrete?

See the photo in post #9.