Extra Wall Insulation

The first day the column associated with this bulletin ran, I knew I was in for trouble. My email box was overflowing with messages both pro and con about the column. Every now and then, I decide to write about a topic that REALLY gets people's critical and judgmental juices flowing. This particular topic - extra insulation in exterior walls - is obviously one of them! There seems to be lots of people out there who think they are energy experts.

While doing research for the column I spoke with energy experts - people who study the topic and do research 40 - 60 hours a week, 50 weeks a year - at the Oregon State University Extension Service and scientists at the Building Research Council at the University of Illinois. I knew that it made sense to add insulation in exterior walls, I just didn't know where the dividing line meandered east to west across our fine nation. These people provided me with the data I needed to make that determination. Too bad I didn't follow their recommendations myself! Of course, I didn't have access to their results - the studies weren't done when I built my house. I happen to have 2x6 walls with a total R-value of 26. If you look at the total heating degree days for Cincinnati, it looks like I might have done better to keep my money in the bank!

Controversy

Many factors were considered when the scientists at the University of Illinois came up with their magic number of 5,750 heating degree days. Among them were the current and projected costs of energy. If energy costs rise faster than they predicted, then the 5,750 number is wrong. The "make sense" number would drop. If energy costs actually become less in the future, then the "make sense" number would rise! The skeptics or those who scoff at their method may use different inflation, interest, or energy cost numbers. Some critics don't even like to use the heating degree method in the first place! Anytime mathematics and big money is part of a column, watch out!

Calculating Added Costs

Let's say you want to figure how much it is going to cost to add 2x6 walls to your new home. What do you need to consider and just how do you arrive at the total cost number?

There are three elements that you have to consider when you modify the thickness of your exterior walls: added framing lumber, insulation, and window & door jamb costs. Labor costs for all of these is practically negligible. Rough carpenters have to bang a few more nails when using 2x6's but it doesn't really add much.

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