After you have turned the key on a finished remodeling job, and paid off your subs and yards, what really makes the project green is its energy efficiency.

Sure, paint choice is important. Carpets matter, too, because they can off-gas. And your green intentions should be expressed in your choice of wood, foam, insulation, and floor finishes, to say nothing of the windows you have spec'd, and the plumbing, light fixtures. But after all the positive impact of these products has been accounted for, what’s really green about a home is how much fuel it uses to heat and cool over its lifetime.

I am not saying these other items are not important. They are. They are essential. But where you really “move the needle,” where you have the greatest long-lasting impact, is when you design a project with a high-integrity, thermal envelope that controls moisture, maintains good indoor air quality and cuts down on fuel consumption.

Here’s why: There are number of ways to calculate a home’s carbon footprint. That’s the amount of carbon-dioxide, CO2, pumped into the atmosphere by human activities like eating, driving, and — mostly — heating and cooling a home. The per-home CO2 contribution is measured in tons per year, and a typical American household can easily contribute between 50 and 70 tons each year for just normal activities. Over 50 years, that household is contributing 3,500 tons of CO2.

Let’s focus on the thermal envelope to see how to reduce that. What products would have a measurable effect? Though remodelers have little control over how a house is oriented toward the sun, you can start with soffit lengths that are geared toward reducing solar gain in hotter months. The length is a factor of your latitude. Google the phrase overhang length and solar gain to find regional online calculators.