100 year old house–insulation for exterior walls/ceiling
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!
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Replies
Jo,
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
We're gardening zone 5, zip code 53095.
Jo,
The DOE climate zone map is posted on GBA's Q&A page:
https://www.greenbuildingadvisor.com/qa
I'll copy the image and include it below.
Thanks. It looks like we need to use closed cell foam to meet R value code.