GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Rim Joist Insulation

ab1989 | Posted in General Questions on

first I would like to thank the members for this valuable site, I have learned a lot here.
– My question is referring to the rim joist area between 1st floor and 2nd floor.
– I am in zone 6
– Just completed framing and I have installed 3″ comfortboard on the exterior. 
– I do not have any hangers in this area so no significant metal that would get cold.
– Everything I have read regarding rim joist says to spray foam.but i think this advice is more so for renovation or houses with no exterior insulation.
– My question is; would using R24 rockwool within the cavity of the rim joist be enough or is there a reason why I should not. As I am trying to avoid using any spray foam in the living areas of the house.

thank you

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. bongo30 | | #1

    I’m doing exactly what you were doing. We are in Zone 4.;We have 1.25” exterior mineral wool on the outside and I do not want to do the spray foam on my rim joists. What did you end up doing? Thanks.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |