Insulating Garage

[bassmann77]

I am going to heat my garage, but figure I should insulate first. All of my walls are drywalled but are not insulated. Should I take the drywall down and insulate or blow in insulation? I don't know about the ceiling yet, but that is also in the plan.

[Eelpout08]

If the sheetrock is not taped yet i would take it down and insulate. I would also doubt there is a vapor barrier behind the rock if there is no insul.

As for the ceiling, you can blow the attic full, and if you need a vapor barrier you can have a few inches of foam sprayed on top of the rock.

[cavalierowner]

Do you plan to DIY this? I will assume yes.

I think I would take it down on the walls too. Mostly because you will need a vapor retarder (barrier). In my experience, you may have a tough time reusing all the drywall, plan on replacing at least some of it. And use a minimum 6 mil poly for the vapor retarder to meet most codes.

The other option you may consider for the walls is to blow in insulation, put the poly over the existing drywall, then apply another layer of 3/8" drywall over that. Before you do that, be sure to think through how you deal with trim around doors or windows, electrical outlets, etc.

As for the ceiling, I will assume that there is an attic space above with trusses. That's where I would be tempted to blow in insulation, put poly over the existing drywall, then new drywall over that. But the new drywall will need to be 5/8", unless you can accept some minor sagging between trusses if using 1/2". Generally, the bottom chord of trusses is designed to take 10 PSF, so another 2.2 PSF of weight added shouldn't be a problem. Also, if you try to use exoposed foam on the ceiling, be sure to check codes; most require they be covered by a thermal barrier (drywall) because they produce toxic gasses when they burn. I also am unaware of any foam that has a perm rating less than 1.0 (the code requirement for a vapor retarder), but I may be wrong about that, since it's been a long time since I looked at the foams. As I think about it, look at the polyisocyanurate with the foil face; it might give you what you need, but be sure to see it it can be left exposed too.

Update: I looked at a couple manufacturers of polyiso and the foil faced sheets do qualify as a vapor retarder, but the must be coverd by 1/2" drywall.

[chad austin]

Be sure to add roof vents if your garage isn't already vented. Ice dams will form in the winter if you don't add ventilation.

[Redlantern]

A bit off topic but not too much. If you insulate the ceiling (vaulted)with rigid foam (blueboard, etc.) and rock it, is there still a need for a vapor barier and soffit/ridge vents? Trying to remember where I heard someone mention that the vents are only needed for batt or blown in insulation in this situation but can't seem to find anything to confirm this.

[cavalierowner]

A vapor retarder and attic venting is required regardless of the type of insulation if it is enclosing a heated space. The foil faced rigid may qualify as a vapor retarder (check manufacturer's literature), but you would need to tape all the joints with a vapor retarding tape to get a complete seal. 6 mil poly is so cheap, it wouldn't make sense (to me anyway) to try to seal all the joints and damage to the foil facing.

[CAMAN]

A bit off topic but not too much. If you insulate the ceiling (vaulted)with rigid foam (blueboard, etc.) and rock it, is there still a need for a vapor barier and soffit/ridge vents? Trying to remember where I heard someone mention that the vents are only needed for batt or blown in insulation in this situation but can't seem to find anything to confirm this.

Yes, since the rigid foam won't prevent the movement of air unless you completely sealed around all the edges, and if you're going to do that you may as well just install a vapor barrier, and I still don't know if it will be legal. Spray foam insulation will seal all the gaps and prevent air infiltration, thus not needing a vapor barrier.

And to answer the OP's question, I would pull the drywall down completely and add a vapor barrier. You never know if there is anything that may need to be fixed hidden behind the walls. And your insulation job will be better IMO.

[Redlantern]

Thanks Caman.

[MNice]

The MN energy code 1322 exempts garages from any requirements. You do not have to do anything, but of course it makes sense to insulate. The attic ventilation is required weather insulated or not and it should be ventilated. They do make vapor barrier paints that are listed and meet any requirements. I wouldn't worry about moisture to much in a garage with the garage doors themselves providing plenty of air changes.

[bassmann77]

Thanks guys for all of the advice/suggestions. I guess I am going to be pulling the sheetrock down and making sure everything is good. The house was built in 2004, so hopefully I won't have to many surprises.

[cavalierowner]

The MN energy code 1322 exempts garages from any requirements. You do not have to do anything, but of course it makes sense to insulate. The attic ventilation is required weather insulated or not and it should be ventilated. They do make vapor barrier paints that are listed and meet any requirements. I wouldn't worry about moisture to much in a garage with the garage doors themselves providing plenty of air changes.

The OP said he was going to heat the garage. The exemption applies to unheated garages or minimally heated spaces. Here's the link to the Energy Code http://www.doli.state.mn.us/ccld/PDF/sbc_1322.pdf The part I'm refering to are the exceptions 1 and 7 on page 3 and the top of page 4; page 1 defines a conditioned space. So if he doesn't design the space to heat above 50 degrees, he doesn't have to meet the energy code.

[MNice]

I've talked to the State many times on this, and garages are exempt, period. You can do whatever you want. Don Sivgney is the guy from the State to talk to.

[cavalierowner]

Boy do I wish I had that guy's name when I called a few years back! Would have saved my client and I a lot of frustration. I talked to a guy in the Building Plan Review department.

[Dave]

And add extra outlets while you have the sheetrock down. Always nice to have them handy.

[Surface Tension]

Are you sure there is no VB under the sheet rock?

Can't tell you how many old homes I've blown insulation walls and ceilings into that did not have a VB.

Personally, unless you suspect issues with the wiring or need to add receptions and lights, I blow it and use vapor barrier paint.

[pikebaybum]

blow the walls, vapor barrier is way overrated.