It's common knowledge that 2x6 exterior walls are more expensive to build than 2x4 walls but provide a larger cavity for insulation. While most people understand this instinctively, it's much harder to calculate whether or not the tradeoff is worth it. Below, we've run the numbers on a random sample of our house plans, using both our advanced cost-to-build calculator and our home energy cost-calculator across two different climate zones so that you can get the information that you need to make a decision.
The Data:
In the chart below, we compared 7 different randomly selected house plans in two different climate zones. Each point on the scatter plot represents one of those homes. It's a pretty clean relationship that scales easily. (Full list of assumptions below for those that are interested)
The average annual energy savings from switching from 2x4 to 2x6 walls was $108 in a warm climate and $223 in a cold climate, while the average total marginal cost to build was $4,145.
At first glance, it seems like a slam dunk for the 2x4 walls. After all, it would take 38 years in a warm climate and 19 years in a cold climate to break even on the cost of upgrading your walls and insulation. But the calculation is more complicated than that since most people build their homes with a mortgage paid over 30 years, while the energy costs have to be paid out every single month. In the following bar chart, we look at the breakeven assuming a 20% down payment and a 5% interest rate.
The tables have turned! If you're going to finance your house construction, then you will see a net return on your investment after 4 years in a cold climate and 9 in a warm climate. Over the life of your 30 year loan, you will save $5,320 in a cold climate and $1,870 in a warm climate. That's pretty good!
This is probably a somewhat conservative estimate because under-investment in energy production is likely to cause a surge in energy prices over the coming decade.
You may have noticed that (unlike other companies) we design our homes 2x6 first and don't offer the standard option to switch between 2x4 and 2x6 walls on our stock home plans. This is because it just doesn't make sense any more to offer it as a standard option.
We do see two exceptions to this rule:
- If you're building with cash
- If you're building a seasonal home
In these rare cases we are happy to help customize your plan with 2x4 exterior walls.
Modeled Assumptions:
Since there's a number of variables, we'd encourage you to play around with the calculators (linked above) to see specifically how different choices can affect your breakeven rate.
- Climates
- Hot Climate: Austin TX
- Cold Climate: Lansing, MI
- Cost Factors
- 2x4 - Wood Studs with R-13 Fiberglass Insulation
- 2x6 - Wood Studs with R-19 Fiberglass Insulation + Door/Window Jamb Extensions
- Electric Cost: $0.137 / kWh
- Nat. Gas Cost: $15 / 1000cf
- Natural Gas Furnace Heat AFUE-91%
- Electric Heat Pump A/C EER-12
- Average Air Infiltration