Hi,
I am the new owner of a brick veneer over wood frame rental property in Kingston, ON, Canada. (5A I believe)
It has been below freezing the past few days but not terribly cold otherwise the past few weeks. Tenants have noticed condensation on the walls in closets and in exterior corners, leading to significant mould growth on the interior surface of the plaster. The issue is worst when in cases where stuff was against the exterior walls. The unit was warm and humid. I gave them a dehumidifier and took things away from the wall. It looks like things are improving, but I suspect I will need to address the insulation in the near future.

building estimated c. 1960.
Construction is (interior to exterior) plaster on wallboard, black plastic sheet not well sealed, 2×4 (3.5″) wall with very thin and loose pink fibreglass, low density fibreboard sheathing, presumed air gap, single course brick veneer.

I cut a hole in the wall and it seems dry inside.

What are my best options here? If possible I would like to leave the existing plaster in place for cost savings, but only if a good-enough wall assembly can be achieved.

Could I dense pack the cavity with cellulose, and then add continuous rigid foam insulation over the  plaster, then strap and drywall?
The cellulose could dry to the exterior and only the existing plaster would be sandwiched between vapor impermeable layers.

Please tell me what I’m missing! Or other assemblies to consider.

Cost is certainly an issue, but we’re looking for an effective and long-term solution.

many thanks in advance.
Ian