Insulating a Minnesota Garage

[Jeremy5431]

Hi Everyone,

I have one garage wall that is not insulated. I would like to insulate and sheet rock the wall this fall. I have a couple of questions, that I hope ya'll can answer for me.

1. What R rating should I get for the insulation?
2. I want to confirm that I'll need to put a vapor barrier up between the Sheetrock and the insulation?
3. The garage has building wrap under the vinyl siding, do I need to put a vapor barrier between the insulation and the OSB

MODs: if this isn't the right board, please feel free to move.

Thanks,
Jeremy

 

[Denwood]

1. Normally this will depend on 2x4 or 2x6 construction. If you're doing spray foam in MN, use closed cell (at least 2") and as much R as you can afford.

2. Yes.

3. No. You only want vapor barrier on the inside. If using closed cell spray foam, you will not need any vapor barrier.

 

[Jeremy5431]

1. Normally this will depend on 2x4 or 2x6 construction. If you're doing spray foam in MN, use closed cell (at least 2") and as much R as you can afford.

I have 2x4 studs. I was planning on using paper backed insulation from Menardss

 

[Showkey]

I have 2x4 studs. I was planning on using paper backed insulation from Menardss

That’s conventional construction, you would the choice of R11 or R13 in craft faced roll insulation witha 2x4 space.

Do you have ceiling in the garage ? Blown in maybe to R38 would be good choice. Ceiling forming an attic is better than rafter insulation against the roof deck.

Foam is great.......but.......it’s a budget buster, especially on garage. Then if you 2” of foam you still need to fill the cavity.

 

[Jeremy5431]

That’s conventional construction, you would the choice of R11 or R13 in craft faced roll insulation witha 2x4 space.

Do you have ceiling in the garage ? Blown in maybe to R38 would be good choice. Ceiling forming an attic is better than rafter insulation against the roof deck.

Foam is great.......but.......it’s a budget buster, especially on garage. Then if you 2” of foam you still need to fill the cavity.

Im thinking about using the attic for storage, so Im considering using a vapor barrier then rolls on top, then plywood.

 

[Don1357]

The thing about the vapor barrier is that it also serves as a wind barrier; a one inch hole in a 4x8 wall can negate the effect of insulation on the entire wall. When you apply it make sure you tape and seal all the seams in order to keep a minimal amount of air moving through.

 

[Denwood]

Consider the flash/fill where you have 2" of closed cell sprayed in, then fill the rest with batt, or blow in cellulose (attic). It's pretty much impossible to beat the efficiency of air sealing with spray foam...

I also did my shop roof which was vaulted during the shop reno...well worth the expense. It's now a non-vented assembly.

So this:

Vaulted after adding LVL cross beams and ridge beam:

ended up as this:

 

[Showkey]

Let’s go back to cost..........

Closed cell spray foam ranges from $0.90 to $1.50 per board foot so 2” foam might run $2-3.00 per sqft @ 2” thick........4” double that.

R11-13 Batt insulation is about .21 per sqft ...........

So foam is roughly 10 times more expensive..............

 

[WisJim]

Around here I am getting quotes of around a dollar or less a board foot for spray foam, installed. The low price of fiberglass batts is just for the insulation. I'm not going to deal with that stuff again, after using it in a lot of old projects, and ending up itching all over and not getting a super fit around electrical boxes etc. Remember also that the spray foam may have twice the R-value also, and does a much better job of sealing against drafts etc.

 

[TractorJeff]

OP states in first post that the outside is wrapped. Theoretically he should have minimal air infiltration. Which means his Menards budget should be fine using R13 and vapor barrier, then sheet rock.

 

[mobetta]

Tyvek keeps out moisture. kind of. and is NOT a vapor barrier.

I put mineral wool in my walls. cost more than fiberglass but its a superior product. r15 for 2x4 walls

 

[Showkey]

There’s another reality check on garages.........insulation is a total building envelope, spending $3000-$5000 on foam and have two conventional garage doors that might be R3-5 makes the building only as tight as the weakest surface. It’s no different than have a completely tight building and have the window open. The air exchange rate and heat load don’t change because you spent a fortune on foam on 3 walls if the complete package is not sealed and tight.

 

[shamus29]

I am working on my new garage at the moment here in Nova Scotia Canada we have similar winters to you, I put r24 in the walls (2x6 studs though not 2x4) and r40 in the ceiling. Vapour barrier between the drywall and the studs.


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[Jeremy5431]

I am working on my new garage at the moment here in Nova Scotia Canada we have similar winters to you, I put r24 in the walls (2x6 studs though not 2x4) and r40 in the ceiling. Vapour barrier between the drywall and the studs.


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Thanks for the photo! thats exactly what I needed to see.

My goal is to take the chill out of the air for those really cold days. Then add a plumbed heater to work in the garage occasionally next winter. While I would love to heat my garage to 40 or 45 in the winter, Im concerned about how much my gas bill will increase and the fact that I need to insulate my garage doors as well. Although my wife has been asking about getting new garage doors lol.

 

[nadogail]

The last garage door I bought was insulated and metal covered on the inside, from now on that is the only kind I will buy.

 

[shamus29]

Not a problem I have insulted door I think r18. I’m not sure if I’ll keep the heat on all the time or not yet but definitely will have heat on after sled trips to melt off the sleds


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[Plump]

I'm in southeastern Wisconsin so no where near as cold as you get, but I used R13 fiberglass batts in the ceiling joists and walls. Covered one wall with OSB so I could nail/screw anywhere and drywall on the other three walls. I have about half of the ceiling covered in drywall with the other half exposed batts with the paper backing exposed to the garage. I have a decent door but not super insulated. I do put on some plastic on the uber-cheap windows in the winter and have a ceiling fan.

All that said, even the small heaters that I've used has gotten me through even the coldest winters. I don't heat it all the time; just when I'm using it, but I do plenty of work and have people over all the time. Even my wife's van heats up the place enough to keep it above freezing most of the time!