I have a soyfoam insulation estimate for the first floor walls of my 40 x 80 sq ft home built in 1976. Is $4250 worth it?

Asked by Blair Frank
Cedar Rapids, IA

I do not know if this is the priority I want now, but I do want to get the house as sealed as possible before getting solar panels. I already have Energy Star windows.


Cynthia Phakos

Answered by Cynthia Phakos

Los Angeles, CA

Koffka Phakos Design

December 6, 2010

Upgrading the thermal envelope of your home by installing Energy Star windows, insulation and sealing exterior cracks prior to getting photovoltaic panels is a very sound strategy.

  • It makes sense to understand the energy usage of your home after you make these improvements, as it might drastically change.
  • You might wait a couple of months after the upgrades and compare the savings before you invest in the solar panels.

In an existing home, adding insulation to the walls can be challenging as they are already finished with drywall. Either you remove the drywall in sections and install insulation, or you drill holes and blow in insulation (cellulose, or injectable foam).

Here are a couple things you might want to keep in mind.

Injecting spray foam into an existing wall may cause problems

I had always assumed that one can spray foam insulation into an existing wall, but in speaking to installers in California I was told that it is difficult, if not impossible, to find injectable foams that meet California’s indoor air quality requirements.

  • Though Indiana has less stringent codes, you might investigate if fumes are offgassed when installing the product you are planning to use.
  • Also, a manufacturer from Florida whom I spoke with brought up the issue that if you inject foam into an existing wall, there are cases where a weak wall might become deformed or the foam might blow out of the wall at cracks and openings.

So let’s assume that you are removing the drywall, in which case home foam insulation would be a very good method. Foam insulation will seal the cracks in the exterior wall, which will then prevent air infiltration.

Open-cell vs closed-cell foam

There are two types of spray foam insulation. For your purposes you will want to use a closed-cell foam (vs. an open-cell foam) if that is affordable

  • Open-cell foams have an approximate R-value of 3.5 per inch (similar to batt insulation) whereas closed-cell foams have an approximate R-value of 6.0 per inch. 
  • The better your wall is insulated, the less energy you will need to condition your house.
  • With closed-cell insulation, exterior walls that are constructed of 4” studs would then have an approximate R-value of 24, which is very high.

Should this be too expensive, there are also combinations that installers will do, where you might just do a ½” layer of foam to seal the cracks and then do a layer of batt insulation.

Good luck; this sounds like a satisfying project.


For more information:

Read Andy Ault's Q&A "Do you recommend bio-based soy foam insulation?"

Also, read Alex Georgiou's Q&A "I want to add wall insulation to my 1920 home. I have two locally available options -- Icynene and Tri-polymer foam. Can you advise me?"

Tagged In: home air quality, insulation, spray foam, solar panels

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