Wall Size and Energy Savings
When you live in a city such as Chicago, Minneapolis or even Moosehead, Maine, it can get very cold in the winter. More importantly, it can stay cold. If energy prices are low and you have an efficient furnace in your new home, you might not care if it is 20 below zero. But energy prices can be unpredictable. They may jump 20 or even 30 percent in a short amount of time.
What's worse, it is very difficult to upgrade insulation to the exterior walls of your home once it is built. As you plan a new home you will come to a fork in the road. Your builder may ask you whether you want 2x4 or 2x6 exterior walls. The first thing you should think about is return on investment since it will cost extra money for the thicker 2 x 6 walls.
There are many ways to make a new home more energy efficient. Hundreds, if not thousands, of books have been written about the topic. But all too often the issue of return on investment is overlooked or glossed over. Many people operate on a tight budget when building a new home. There can be lots of hand wringing over decisions where you can't see an aesthetic result or an immediate economic result. Thicker walls that contain more insulation is absolutely a mundane topic that would fit nicely in this category. But fortunately there is a way to measure a distinct return on your investment for an upgrade to 2 x 6 exterior walls vs. 2x4 exterior walls.
The upgrade to 2x6 exterior walls is easy to understand. These wall require more expensive lumber, added finish lumber for the extension jambs for all windows and doors and the added cost of the thicker wall insulation. It is very easy for this upgrade to exceed $1,000.00 if not more for an average size home. Fortunately it is a one-time expense that can produce large savings in certain situations.
Several years ago scientists at the Building Research Council at the University of Illinois put some thought into this subject. The results of their research were very interesting as they established a benchmark that allows a person to quickly determine if upgrading to a thicker exterior wall system is a good idea. Using historical weather data, heating energy costs and the cost of the upgrade, they discovered that if you live in an area that experiences 5,750 or more heating degree days per year, it is a good idea to upgrade to the thicker walls.
Heating degree days are calculated for you by the National Weather Service each day for each city. Annual totals are also readily available for hundreds of cities and towns across the USA. But if you want to do the calculations yourself, it is easy. Simply determine the average temperature for each day. Do this by adding the low and high temperature together and then divide that sum by 2. The result is the average temperature for that day. Subtract that number from 65. The result is the number of heating degree days for that day.
If you do this each day, you will discover that Chicago has approximately 6,500 heating degree days per season, Minneapolis has nearly 8,000 and those in Moosehead, Maine will top 8,500 in an average winter. Obviously it makes sense to build with thicker 2 x 6 exterior walls in these locations.
There are some added benefits as well to thicker walls. The greater mass can help deaden sounds. This may be a reason to do it if your home is in an area where the heating degree day total falls below 5,750 or is borderline. If you are trying to re-create the look of an older home, the extension jambs at the windows will help to support the illusion of a Victorian or Colonial home. In my own home, this added space within the extension jambs created a perfect spot to hide my retractable window screens.
You can also work to save energy in your attic no matter which size exterior walls you use. After the insulation is in place, consider installing radiant barrier chips. These highly reflective pieces of material bounce heat back to its source. In the winter months they will send the invisible infrared rays that have leaked into your insulation back down into your living space. In the summer, these magical chips bounce the hot attic infrared energy back outdoors. But never forget that wall thickness is nearly impossible to change once your home is built. Choose wisely and you will never regret it. Choose poorly and you may suffer for a very long time.