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

Insulating rim joists

amcpoppe | Posted in Energy Efficiency and Durability on

A portion of my house (2 bedrooms) are significantly colder than the rest of the house partially because they are the furthest from the heat pump but also the walls are cold to the touch which makes me think it is partially an insulation problem. I have been reading different articles and questions off this website and I was planning on insulating the rim joist in our Daylight basement as well as spray foam at penetrations and gaps in insulation around doors.  The basement is a finished basement but has drop in acoustical tile ceilings so we are able to access above the ceiling.  Some rim joists have batt insulation on them and some have nothing.  I was wondering if it was worth taking out all insulation and just putting rigid insulation (R-10) everywhere or just fill in the places that don’t have insulation.  Also 1 rim joist has multiple electrical wires attached to it (as well as penetrations) as it is right above our electrical panel.  How should I insulated this joist?  Do  I apply rigid over it? I live in Seattle Washington which is zone 4C I think….Thanks!

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. Expert Member
    BILL WICHERS | | #1

    I’d look for ways to air seal before trying to add insulation to those cold walls. There is usually a pretty good “bang for the buck” with air sealing. Check around windows to make sure things are sealed properly. Check window seals themselves too, especially on double hung windows. Check around doors, and make sure weatherstripping in the door frame is around the perimeter where it’s supposed to be and that it’s not squashed so flat that it no longer makes a good seal.

    In the area around your electric panel, I’d try to get a piece of rigid foam behind the wire and against the rim joist, then seal it around the edges with canned foam. You can use canned foam to seal the holes the wires go through too. I’d use a spray foam kit for all the other areas of the rim joist.

    If you aren’t getting enough warm air into those cold rooms because they’re too far from the heat pump, you might try a fan. Sometimes some more air movement will be enough to even out temperatures in a few problem rooms.


  2. Peter Yost | | #2

    Hi amc -

    Your building sounds like a great candidate for a home performance assessment, including a blower door test for air tightness. In the building science order of things: manage bulk water first, then air, then thermal (insulation last...).


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |