I am closing the ceiling of my garage, and wanted to do a few things before that was completed. It's a 2 story house, and there is a shared wall between the house and the garage, on the second story. On the garage side this is above the level that the ceiling will be installed at - so will remain a cold spot. I thought I would add some extra batt insulation to the garage side of the wall. This wall would already have insulation in it(from when the house was built), and a vapour barrier on the house (warm side) as the garage is unheated. THere was also a house wrap on the garage side (exposed) and I put the new insulation right against that. I added the insulation against this wall, and used a sheet of plastic over that to keep the extra insulation in place. It now appears that I created a moisture issue, as there is moisture trapped between the extra insulation and the plastic used to keep it in place. I'm located in a Zone 3 area (Canada, just above ND), so considered a very cold climate during winter. I think the issue is because I used the plastic to hold it in place - can anyone confirm. Then any thoughts on what else I could use to hold the insulation in place, but not trap any moisture? Thanks
Yes, you caused the problem by putting plastic (vapor barrier) on the cold side of the insulation (and having two vapor barriers in the wall.)
You can use mesh nets (commonly intended for holding cellulose insulation.) You could use housewrap, in theory, anyway - its an air but not vapor barrier, that's the whole point of house wrap.