Insulation of Old Concrete Block in Climate Zone 6 – GreenBuildingAdvisor

Hi

I’m looking to insulate and finish a basement room made of concrete blocks. The foundation exterior walls are covered with a delta membrane and damproofing (bitumen material-black stuff).

The concrete block foundation was built are 1960s. It is an extension to my house built in 1950.

I live in Quebec City with a climate zone of 6.

The room has 12 inches above grade and 65 inches below grade.

I wondering which insulation and vapor barrier to put in that room. I don’t want to degrade the concrete blocks. I’ve heard that freeze-thaw cycles of humid concrete block deteriorates them.

The blocks rows are uneven. With rigid insulation, there would be air pockets on rows that are a bit recessed.

This is not a living space, it will be used for storage. I plan to constantly heat it at 18C (64.4F) and run a dehumidifier. I plan to leave the bottom 12-24 inches uninsulated and unfinished because my sector is prone to sewer backup.

I’m having a dilemma. 

• XPS – I would like the simplicity of XPS but I fear there will be air pockets between the XPS and the concrete blocks. I’m thinking 1 inch with a 1.1 perms or 1.5 inches with a perm of ~0.7.

• Rockwool batts – I find it interesting because they would follow the wall form and I could use a smart vapor barrier on top of it. I’m thinking of the Membrain by Certainteed. 1 perms when air is not humid. 10 perms when air is humid. For fixing the wool, I hesitate to drill holes into the concrete blocks. I don’t want to damage them.

• No insulation to take as less risk as possible.

I really wonder what vapor permeability that I need. Would leaving the bottom 12-24 inches exposed allow all the blocks to dry?

Any recommendations?