We have a house with a tuck under garage in climate zone 7. Insulated in walls and ceiling with R-21 fiberglass and polyethylene vapor barrier facing the garage interior. Drywall taped. The garage door is insulated, R-8 at the worst and R-18 at the best, but we do not know the R factor at this time.  Our intent is to make it usable space and not put cars in there.

 

My wife is very allergic to mold and so I have concerns about mold developing in the garage. I’m trying to figure out what to do about the sieve that a garage door is and what to do about HVAC for that space. Preferably want to do it in a low cost way. One way to do this, I figure, is to box in the garage door with a false wall over it. In that case, I’m concerned about the garage door’s colder temps hitting the false wall. How could I mitigate this? I was thinking of treating the garage door as siding, then reverse-engineering the assembly. Meaning, I would add strapping to the interior side of the garage door, add Roxul, then build the false wall against this Frankenstein. In this case, I’m concerned about thermal bridging from the areas where the garage door will remain attached to the wall and overlapping the drywall, beneath the false wall. I’m also thinking about the humid and cold air that would be be trapped between the garage door and the wall. If going this route, I would then buy a separate HVAC for the garage to keep the air separated. 

 

Does anyone have experience with mold in garages and the technical acumen to know if going this route would be setting us up for problems later? Saving money and preserving value but creating a problem that would cost even more to fix at another time?

 

The other way to do this is to remove the door and build a wall in its place. The quote I got for this is $17,000, however. That’s a lot to spend on a house we’re just moving into, and as a novice, I couldn’t do this work fast enough to outrun the first early frost. If I went this route, this would become a true part of the building envelope, and I would add a return duct in it as well as a supply duct. The HVAC is just on the other side of the garage wall.

Thank you!