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Foam insulation

When you add on to your house, consider adding an extra layer of insualtion to the outside of the exterior walls. For years, builders would add some type of insulation to the inside of the walls, known as the wall cavity. We still install this type. But, many of us like to add what looks like styrofoam to the outside.

When building in the winter or the summer months, the extra layer of insulation will help keep the new room at a comfortable tempurature while all of the sub-contracotrs finish. Traditionally, all of the electrical and plumbing must be installed into the walls before the insulation is added. By putting foam on the outside, it gives the subs a bit more time to get their trades done, without costing the homeowner more on their electrical bill.

A 1 inch layer of foam insulation gives an R value of 5. Even as late as the 70's, some homes were built with a final wall cavity value of R-11. Nowadays, in a 2x4 wall, we install at least R-13, so by adding another 5 points to the thing, we are increasing the R or resistance value all of the way up to an 18. Builders used to have to go to a 2x6 wall to get this level of performance.

One surprising benefit of installing foam insulation is noise absorbtion. Many homeowners have told me that they are surprised how quiet their new room is in comparison to the existing house. That is because foam has an ability to absorb noise. Many siding companies are now attaching a foam backer onto their product, and advertising it as not only extra insulation, but also a noise reduction mechanism.

Talk with your builder about installing foam insulation on your new addition.


Kevin Robinson is a building consultant. He is formally educated in general residential construction as well as "schooled" on the job. Formerly licensed as a general contractor in the State of Idaho, he currently shows potential owner builders how they can save thousands managing it themselves.  He has written guest articles for a few construction type  magazines and also publishes his own small newsletter for owner builders. Email Kevin at


Next time, hire a building consultant!.

Comment balloon 4 commentsKevin Robinson • October 25 2009 07:57AM


I don't understand you are adding foam to the outside of the exterior wall?  So how does that look and how does it hold up?

Posted by Elite Home Sales Team, A Tenacious and Skilled Real Estate Team (Elite Home Sales Team OC) over 9 years ago

Thanks for commenting. We still install siding over the top of the foam. The foam is a layer between the siding and the wall shearing.

Posted by Kevin Robinson, Fractional Developer over 9 years ago

Kevin....good post.....I have a subdivision now where the builder is using rigid foam insulation....great R factor...

Posted by Barbara Todaro, Marketing Agent for The Todaro Team (RE/MAX Executive Realty ) over 9 years ago

Of course, make sure you are not getting that foam stuff that replaces the sheeting that is produced nowdays.   I think any extra insulation in a home is a good thing.

Posted by Epcon Communities Epcon Columbia (Epcon Columbia, SC) over 9 years ago