Number 5 in my list of the top-10 green building priorities is to build smaller houses and optimize the use of materials.

While the trend has begun to turn around, we've been building larger and larger houses for decades. In 1950, the average house in the U.S. was about 1,100 square feet, while there were about 3.4 people per household, according data I compiled for a 1999 article in Environmental Building News. The U.S. Census Bureau reports that in 2009 the average new house in the U.S. was 2,438 square feet (down slightly from 2,518 square feet in 2008), while the average household size was 2.6 people. In the past sixty years, house size has increased 120%, while family size has dropped 24%, so square footage per family member has nearly tripled (from 324 to 938 square feet).

From an environmental and energy standpoint, building smaller houses is a winner. Smaller houses take less material to build and they use less energy to heat and cool. This is common sense, but it's amazing how rarely people think about it. For the same EBN article referenced above ("Small is Beautiful: House Size, Resource Use, and the Environment"), we ran some numbers comparing the annual energy use of two homes in Boston: a reasonably well-insulated, 3,000 square-foot house (R-19 walls, R-30 ceilings, double-glazed low-e windows); and a poorly insulated, 1,500 square-foot house (R-13 walls, R-19 ceilings, double-glazed non-low-e windows). Based on energy modeling by Andy Shapiro of Energy Balance, Inc., heating and cooling costs for the poorly insulated, compact house totaled $421 per year, while heating and cooling the reasonably well-insulated, large house totaled $635.

The larger house is more energy-efficient (it might even meet the standards for green home certification), but its total energy use is 50% greater than that of the smaller house. This isn't meant to suggest that we shouldn't insulate our houses well if they're small, but rather to illustrate just how significant size is to the energy consumption of a house.

Very significantly, the smaller house will also likely cost less to build--even if higher quality, more expensive materials are used. When I hear that green homes cost more than standard homes, my first response is always to point out that smaller homes are much greener--and those homes usually cost less, not more.

Be aware that creating successful compact houses isn't only a matter of shrinking the dimensions. Designing small homes that feel spacious and are comfortable requires a skilled architect or designer. Expect to spend more for a design that minimizes square footage yet feels spacious and comfortable. The investment in design will be paid back during construction--and lower operating costs.

Optimizing the use of materials

In addition to building smaller, there are other ways we can save materials--and money--in building. A few of these strategies are listed below:

• Use standard ceiling heights. Materials cost and cut-off waste can be reduced by building to the standard dimensions of studs and drywall.
• Build on a standard two-foot or four-foot module size. House dimensions of 28 feet by 36 feet for example, will use about the same quantity of materials as a house that's 26-1/2 feet by 34-1/2 feet, because lumber and sheet goods come in multiples of two or four feet.
• Use "advanced framing" techniques with wall and roof framing 24 inches on-center, single top-plates with rafters set exactly above studs, wall corners produced with three rather than four studs, and the elimination of unneeded framing at window and door openings. Not only will advanced framing techniques save materials, they will also improve energy performance, because there's less wood and wood doesn't insulate as well as insulation.

Both of these strategies--building smaller and optimizing materials use--save money during construction and reduce energy consumption. It's a win-win solution that's become all the more important in our highly constrained economy.

My top-10 list of green building priorities so far:

#5. Build smaller and optimize materials use

#6. Ensure durability and reuse existing buildings

#7. Protect and restore the site

#8. Use green materials

#9. Create resilient, climate-adapted buildings

#10. Make it easy for homeowners to be green

In addition to this Energy Solutions blog, Alex writes the weekly blog Alex's Cool Product of the Week, which profiles an interesting new green building product each week. You can sign up to receive notices of these blogs by e-mail--enter your e-mail address in the upper right corner of any blog page.

Alex is founder of BuildingGreen, LLC and executive editor of Environmental Building News. To keep up with his latest articles and musings, you can sign up for his Twitter feed.