GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter 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

100 year old house–insulation for exterior walls/ceiling

WIGranny | Posted in Energy Efficiency and Durability on

We’re gutting a 6×15 area, originally a pantry, to add a tiny powder room and walk thru pantry. The exterior sidewalls are 3/4″ pine boards with redwood clapboards. About 15 years ago we stripped the claps, used oil based primer and 2 coats of high quality latex paint. There is no housewrap, but some red rosin paper under the claps. The roof is sound with no leaks.

Above the space is an open-air porch with a very slight hip roof. The roof joists are 2×8’s. Using batt insulation for the roof will be a nuisance, and won’t meet code for Rvalue. We’d rather not drop a ceiling to add thicker batts.

The walls are full 2×4’s. We don’t have any moisture problems, rot, or mold.

Is this a good application for closed or open cell foam? Is one brand superior, or more cost-effective? Hubby is skilled at renovations (kitchen, garage, full bath, he’s done it all.) How much should we put in the ceiling? How much in the walls?

We’re in WIsconsin, and this space is on the north side of the house. It doesn’t get much sun. It’s exposed on all sides to the exterior.

Thanks for any/all advice!

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. GBA Editor
    Martin Holladay | | #1

    Depending on where you are located in Wisconsin, you are in climate zone 6 or 7. If you are in climate zone 6, the building code (2009 IRC) requires at least R-20 wall insulation and R-49 ceiling insulation.

    Your 2x8 ceiling joists are probably 7.25 inches deep. If you install 7 inches of closed-cell spray foam there, you'll end up with an R-value of about R-44 or R-45 -- not quite the minimum code requirement, but close. Any other type of insulation (except rigid polyiso, which is hard to install between joists) will give you even lower R-values.

    Your 4-inch-deep wall studs will give you room for about R-25 or R-26 of closed cell spray foam. Open-cell spray foam or cellulose will give you about R-14 or R-15.

    For more information on the range of insulation options, see the GBA Encyclopedia:

    Insulating Roofs, Walls, and Floors

    Insulation Choices

    Batt and Blanket Insulation

    Blown-In or Loose-Fill Insulation

    Rigid Foam Insulation

    Spray Foam Insulation

  2. WIGranny | | #2

    We're gardening zone 5, zip code 53095.

  3. GBA Editor
    Martin Holladay | | #3

    The DOE climate zone map is posted on GBA's Q&A page:

    I'll copy the image and include it below.

  4. WIGranny | | #4

    Thanks. It looks like we need to use closed cell foam to meet R value code.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |