Basement reno - How do I effectively insulate my basement?

Steve J
Updated: Aug. 3, 2020

How do insulate and integrate insulation for the wall, floor and rim joists?

Details: 2-story house built 1983, located in southern Ontario (GTA). Poured concrete foundation. Floor joists sit atop the foundation wall on a rim joist wood-sill assembly (not imbedded in concrete). I have removed existing drywall, 2x2 studs, 6mm poly, r12 fiberglass insulation, and tar paper everywhere except laundry room, mechanical area, and beside stairs. Total basement sqft is approx 800. Livable space: 650sqft.

My plan for each surface:

  • Concrete Foundation: Durofoam EPS (1.5" or 2"?) +wood stud with Rockwool R14 +Drywall +moisture/vapour barrier laytex paint. Which EPS thickness should I go with?
  • Concrete Slab: DMX aiflow dimple mats +(3/4" EPS, needed?) +OSB +flooring of choice
  • Header/Rim Joist: Not sure... Since this is above grade, but in the basement, how do I layer this and tie it into the wall insulation method described above? Do i add Acoustic sealant around gaps in the rim joist and sill plate Or Expanding foam? Next would I fill rim joist cavity with Rockwool, then EPS + Drywall? or Just sandwich+seal EPS panels to build it up to the foundation wall insulation?

Specific order:
After gluing the EPS against the concrete foundation, sealing the seams (PL300 and vapour tape): Should I then proceed with installing the DMX dryflow underlayment +(3/4" eps?) +OSB floor, then build the external/internal wood stud walls? 
How do the DMX and EPS on the wall tie together? Do I still maintain a 1/4" gap around the perimeter (as per DMX installation)? I guess the idea is that this allows it to air dry if any small amount of water enters the basement. Does this create a problem within the new wall? 

Other questions:
How do I adequately insulate around water meters, electrical panel or rough-in pipes that are very close/adjacent to the exterior foundation walls? 

Also, will there be an issue with thermal bridging or vapour with having one insulation system (old) adjacent to another (new) and only separated by wood stud?

Many thanks.

Responses (2)

Steve J 5 years ago

Hi, thank you for the detailed reponse. Referring to the Q&A on Header/Rim Joist insulation method, I have seen some sites (including .gov) use EPS against the Rim joist, using foam to seal the edges and then rockwool. Is there a difference to the order?
Also if I wanted to air seal this area could some type of caulking also be used directly against the rim joist/floor joist area? if so, what type?