Ceiling insulation question for a detached midwest garage

Hello - I'm trying to figure out how I should insulate the roof of my detached garage. I've read a bit on here about the methods, but I'm wondering if there are specific recommendations for what this roof looks like.

The garage is in the Chicago area, and was built by a contractor. My goal is to be able to work inside it on most hot days, and most cold days - but if it is super cold and I can't get heating and insulation to make it comfortable, missing those days is fine.

The garage has a pyramid hip roof, with two vents near the top on two of the four roof planes. The garage is about 20' by 20', and the roof is probably from about 8' high off the ground to 12-13' off the ground. So far, my plan is to use R-13 faced fiberglass batt insulation on the walls - correct me if that is unwise, I haven't gotten far into installing it yet.

For the roof, I was looking at hiring a contractor for spray foam, but based on the pricing I've seen and the process, it might be beyond my hoped-for budget. Is there another way to do that roof that would work for this style garage? Also, I'm just planning to use that space for storage, once I get it insulated.

Thanks for any advice!

Maybe you could glue foam board to the underside of the roof sheathing?

I don't know how much I'd be willing to "stack" on those rafters, as they're not engineered trusses.

The common misconception people make is thinking they can stack everything up in their garage attic, when the wood was never designed to handle the load they're adding.

Personally I would run R13 or R19 (it appears to be a 2x6, so r19) between the rafters, and then run r30 the other way on top of it (it's about 10 inches thick).

If you wanted some boxes or something of LIGHT stuff to store up there, you could build a few legs that screw in the bottom chord of the rafters you have (10 inches tall so it clears the insulation), and stick a sheet of 4x8 OSB or plywood on those feet, so you have 32 sqft of LIGHTWEIGHT storage, over many rafters, up in your attic.

DO NOT a glue foam to the bottom of the roof deck !!!!!

If you insulate, you do exactly the same at the home.
Build out the ceiling Joists for support and drywall the garage ceiling.
Then insulate the ceiling with batts or blown in.
The idea is the attic area Temperatures should be as close outside as reasonable. The roof deck needs to cool in summer and cold in winter. Cold in winter stops ice dams and cool in summer prolongs the life of the shingles.

Attic area should be vented.
R30-38 in the ceiling is the minimum.
Obviously the walls would be batt insulation and covered.







Spray foam the roof deck is another choice.......Very very very expensive, limited depth and still has to be covered, also not a DIY job.

Showkey said:

DO NOT a glue foam to the bottom of the roof deck !!!!!

If you insulate, you do exactly the same at the home.
Build out the ceiling Joists for support and drywall the garage ceiling.
Then insulate the ceiling with batts or blown in.
The idea is the attic area Temperatures should be as close outside as reasonable. The roof deck needs to cool in summer and cold in winter. Cold in winter stops ice dams and cool in summer prolongs the life of the shingles.

Attic area should be vented.
R30-38 in the ceiling is the minimum.
Obviously the walls would be batt insulation and covered.







Spray foam the roof deck is another choice.......Very very very expensive, limited depth and still has to be covered, also not a DIY job.

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I totally agree with this, you need to create an attic space. Since you already have the vents installed, you are one step ahead of the game. You always need air flow underneath your roof deck. Just insulate the ceiling

Thank you for the help! I'm new to this so it took two times reading through to fully understand, but it makes sense now - close off the attic space, and insulate the ceiling, allowing the attic to still have air flow. I also understand the point that the ceiling joist aren't meant to be load bearing for a bunch of stuff, so I'll be careful about that.

I'm going to look up guides on how to create the garage ceiling out of what I'm starting with.