Interior wall is now an exterior one

I have a basement garage that had a large unused room between the garage and the finished portion of the basement. The room had the heat pump condenser and air handler and was unheated. I demolished a partition wall between the room and the garage so I could store an old car there.

Later on I noticed the wall between the finished basement and the new portion of the garage was cold during the winter. I open up an exploratory hole and, oops- no insulation. My new "exterior" wall is a 12' long energy hog.

There is a soffit on the top of the wall that can be reduced in size if I redo the room, so I can use that to get access to the top of the wall. I'm thinking about using cellulose insulation and blowing it in there between the studs. The problem is that I won't have a vapor barrier.

Is this going to be a problem?

Assuming you live in a high humidity area, condensation will be a factor. Also, code requirements call for the wall and doors between your garage and dwelling must be fire rated. You likely don't have that now and your insurance (and local inspector) wouldn't like it. As part of the fire rating, you may need fire blocking in the wall studs, which would make installing blown-in insulation more difficult since you'd need more holes to get around the blocking.

Changing the use of space needs to be worked out, and it doesn't seem like you did any in the project. Depending on the climate, the vapor barrier location can sometimes shift from the inside wall to the outside wall, so you'd want to do it right for your particular area. Up north, where the perponderance of HVAC is heat, the barrier is towards the inside. Blown in cellulose is good in that it doesn't allow much air intrusion like fiberglass can, but if it does get damp, it will take a lot longer to dry out and is great mold food. You might want to consider injecting with foam which would be better insulation, stop air intrusion, and would (most anyways) act as a vapor barrier as well.

To up that wall to fire code, you'd likely have to either replace the current drywall with fire rated, or maybe just add a second layer. that won't cover fire blocks, if required as well. It doesn't sound like you pulled a permit.

Code requirements when I demolished the wall (SBCC) as well as current require 1/2" gypsum board, any type. They also require an insulated metal door between the garage and living space, and I simply re-used the old insulated metal door to its new barrier location. There is no fire blocking requirement except between stories. Buy anyway that has nothing to do with my question.

I'd like to use foam, but I'm not happy with the costs that I'm seeing, especially for such a small section of wall due to set-up charges. Unless the outside garage doors are open, the garage was seldom less than 55F before I took the wall down. Plus the finished space is my office, which I like to keep dry anyway. I'm not sure that moisture intrusion into the insulation is a big deal.

WHere I live, they require fire rated drywall on both the wall and the ceiling (if the space above is living space). Plus, the fire wall must extend up to the roof on the facing wall.

There are some larger foam kits you can buy (not the little cans) that would allow you do to a small wall relatively ecconomically.

Pretty much just regular 1/2" gyp walls and ceilings. No type X or anything special. They did up the ductwork requirement a few years back requiring hard pipe passing through instead of flex and that that stung my HVAC guy. And fire caulk penetrations.

Where does one typically buy/ rent these foam kits? I have never seen them.

This is just one of many I got while googling...http://www.foampower.com/index.php

Wow- thanks! It looks like the "Handi-Flow Pour in Place" is what I need. I guess I didn't google the right terms.