Insulation and vapor barrier?

[BigE]

My garage is currently uninsulated on all but the side it shares with the house. It is just under 500 sq ft and attaches to the left side of my house. The house is on a crawlspace and the garage is on a slab with no connection between the two spaces. However, the house attic is structurally connected to the attic over the garage. It is mostly separated by some OSB because the builder went a little overboard on the roof sheeting. I intend to cut it back so I can walk into the garage attic from the house attic. The garage is fully sheetrocked with a popcorn ceiling. However, there is no insulation in the outside walls or the ceiling. I want to be able to heat the garage in the winter. Is it recommended to rip all of the sheetrock down, install insulation and vapor barrier and then rerock? In other words, will I run into moisture problems if I just insulate and don't take the drywall down to install vapor barrier?

 

[440-6 Shaker]

It has been my experience that regardless of location anytime you're going to be seasonally heating a space and having mixtures of cold exteriors and warm interiors you should put a vapor barrier on the warm side.
Too bad your garage is already rocked, its such a messy job to tear out perfectly good drywall.

 

[pattenp]

You can use batt insulation with the kraft face for the ceiling and do blown in for the walls and use a vapor barrier primer sealer paint on walls. Or do all blown in and vapor barrier primer sealer paint on walls and ceiling.

 

[1299]

If my ceiling is already sheetrocked, can I lay the kraft faced down and not staple it? My bottom chords of the trusses are 2x4, so it looks like R15 is the max.

 

[pattenp]

If my ceiling is already sheetrocked, can I lay the kraft faced down and not staple it? My bottom chords of the trusses are 2x4, so it looks like R15 is the max.

It's not the ideal way because it does not provide a sealed vapor barrier, but it can be done that way.

 

[1299]

How else would I seal it? Go unfaced and use 6mil plastic?

 

[spruce]

sprayfoam if the budget allows.

 

[socapots]

Leave that barrier between the two attics. Make sure there Is no existing vapor barrier in the garage ceiling. If there is just blow in some cellulose or fiberglass. Go as thick as the R value you want.

If there is none then put some up re-sheet and blow the insulation in.

 

[pattenp]

How else would I seal it? Go unfaced and use 6mil plastic?

That is an option. You would be able to get a tighter seal. If your garage is going to be heated or cooled occasionally I don't know if the vapor barrier not being prefect is that big of a deal.

 

[Kevin C]

If my ceiling is already sheetrocked, can I lay the kraft faced down and not staple it? My bottom chords of the trusses are 2x4, so it looks like R15 is the max.

You can put in one layer of R15 and then add a layer of unfaced R30 on top of that at a right angle.

I wouldn't be too concerned about the vapor barrier not being tight to the faces of the trusses. Painted sheet rock acts as a moisture retarder. The Kraft paper also helps but does not need to be perfect. The opposite side of the insulation will have not problem dissipating moisture since there should be nothing on top of it.

I would add some type of air space at the edges.

My 1921 house did not have insulation when it was built all I did was put in Kraft paper faced R15 facing side down ( paper facing the living space) and then put R30 over that at a right angle.

 

[1299]

You can put in one layer of R15 and then add a layer of unfaced R30 on top of that at a right angle.

I wouldn't be too concerned about the vapor barrier not being tight to the faces of the trusses. Painted sheet rock acts as a moisture retarder. The Kraft paper also helps but does not need to be perfect. The opposite side of the insulation will have not problem dissipating moisture since there should be nothing on top of it.

I would add some type of air space at the edges.

My 1921 house did not have insulation when it was built all I did was put in Kraft paper faced R15 facing side down ( paper facing the living space) and then put R30 over that at a right angle.

Air space like vent chutes?

 

[BigE]

I just realized that my whole house is insulated, but not vapor barrier'ed. Admittedly, its temperature is much more regulated than the garage will be, but I don't live in an area where it gets extremely cold. I'm thinking I'll be okay with just insulation in the garage, especially since I don't plan to cool it, only heat it.