Solid Foamboard good for small partition office in garage?

Hossenfeffer

I plan to make an 8X15 office partition at the end of my new large unheated, uninsulated attached garage.

The construction of the partition and ceiliing are going to be easy. I will need to put in electrical baseboard heaters (also not a problem).

However, the outer 3 walls of the office partition will need some insulation (maybe even my ceiling). The actual partion wall will be a stud wall and I could put regular bats in that. But the outer wall of the garage is the one I would like to just glue foamboard onto the drywall...and maybe the ceiling.

QUESTION: Do I need a vapor barrier anywhere on either the outer wall or the partition wall. At the moment, I can see that the outer wall has no vapor barrier because it is not a heated living space and not insulated.

What about the inner partition stud wall with bats? Need vapor barrier anywhere there?

Thanks for any tips. Please ask if you need more info or a sketch.

detailedEye

If you use foamboard (polystyrene or better) and seal the seems it doubles as a vapor barrier. You should have a vapor barrier on the outside walls for certain. I assume when you say you want to glue FB to the drywall you mean under the drywall. FB must be covered with drywall to create a fire block.

I think you'll want a vapor barrier on the warm side of the partition walls, kraft faced batts would be a minimum, otherwise you're relying on the drywall & fiberglass to stop the flow of warm air into the cooler part of the garage. Fiberglass does not stop air flow, it only slows it down.

If you're not going to use this space everyday and keep it heated in the winter than the vapor barrier on the partition walls is probably not a big issue.

Why not just use batts? Fiberglass is cheaper than FB.

vsheetz

Converting garage space into living space typically needs to be approved and permitted - some cities are very perticular about garage conversions (mine is, for one).

nap

I believe most areas require permits. Not only due to it being a major alteration which involves safety and general building code issues but it increases the square footage of the living space so they can now increase your taxes.

Hossenfeffer

Thanks so far. Yes, I was thinking of just gluing the foamboard to the exterior inside wall of the garage for insulation, but now that you mention fire, I guess I will just add another row of studs on the inside of the uninsulated garage wall and put bats in there. It will take up another few inches of space and require drywalling another wall and a vapor barrier, but I guess it is the right way.

Yes, I was always going to use bats in the partition wall. Thanks to your replies I know now to put the vapor barrier on the inside (warm) side of that wall. I thought so.

Permits, eh? I bet you are right.

detailedEye

I'm confused by your plan for the exterior wall. What do you mean by another row of studs? Is there a finished wall there now? Or is this a concrete wall of some sort?

Hossenfeffer

Ah, a picture solves so much...it is not easy to grasp the idea when I described it.

Yes, the new space will use the finished end wall of the garage as one wall. It is drywalled, but not insulated, nor does it have any vapor barrier (I cut a central vacuum outlet through it the other day).

I suppose I could have insulation blown in if I wanted to avoid lining that wall with another row of studs and put in bats, but it still would not have a vapor barrier if I just blew in some insulation.

detailedEye

Tear the drywall off and insulate the existing wall. Then put up new drywall. This is less work and cheaper than what you're suggesting. Not to mention you could run into mold issues by stacking insulation and a vapor barrier on top of drywall with no insulation behind it.

There should be several topics on this website about how to insulate things correctly.

Hossenfeffer

Got it! That sounds smart. Now one last little wrinkle. That existing exterior wall that I will tear the dry wall off to insulate because I want it as one of the walls of my new space, is higher/taller that the space I am creating.

In other words, the wall is maybe 12 or 13 feet high and the ceiling of my new space will be coming off it at only 8 feet. Part of the ceiling is a mezzanine storage area build onto the wall and I will be extending that out (adding posts to the floor) and using that as the ceiling of my new space.

So, do I have to tear off and insulate all 12 feet high of that wall , or tear off the bottom 8 feet of wallboard, put in a vapor barrier along the 8 foot level and then out and down over my new baffle insulation. I hope the latter will work because I can't open up the entire height of the wall with the mezzanine there and it is too high and probably overkill anyway.

Thanks for all the tips so far, gentlemen.

Gary in WA

You might take heed the advice to go through your local Building Department. If you are in the Southern U.S., the vapor barrier would be wrong.... You also need a fire-rated, self-closing, weather-stripped door, proper light and ventilation, possibly a means of egress (escape) other than through the burning garage (per code), possibly 5/8 drywall near the garage, etc. The cars put out a lot of moisture just after parking that would end up inside your new walls to rot...

Be safe, Gary

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Hossenfeffer

Thanks GBR. I am actually not very far from you.

All your points are in play here as well. I am going to double check with city hall permits office.

All features mentioned are "do-able" even if a bit more costly. I think the extra door to the outside will be the most challenging and expensive.

meboatermike

In some jurisdictions I believe the required extra egress can be me with windows perhaps. Check with your code enforcement office