Industry Market Trends

Want to Build Green? Start by Thinking Small.

Sep 12, 2011

Tiny cottageLast week, I wrote about the home design movement that is making a virtue out of living in small dwellings. (See "Living in Small and Tiny Houses -- Thoreau Would Be Proud.") Let's consider now some of the environmental implications of living in smaller spaces. (Photo: Tiny cottage. Credit: RowdyKittens, CC BY 2.0.)

According to the National Association of Home Builders (NAHB), the average new single-family home size in the U.S. has been decreasing since the beginning of the financial slowdown in 2008. The average size peaked in 2007 at 2,521 square feet (SF). Preliminary data indicate that had dropped to 2,377 in 2010. NAHB expects it to drop further to 2,152 SF in 2015.

The chart below shows the distribution of new home sizes predicted by NAHB for 2015. Most homes, 63 percent, are expected to fall in the 2,000-2,400 SF range. About 15 percent of homes will be smaller than 2,000 SF, with only 2 percent smaller than 1,600 SF.

Projected US new home sizes in 2015


However, the recent decline in house sizes goes contrary to the general U.S. trend since the 1950s, according to Rick Diamond and Mithra Moezzi, of Lawrence Berkeley National Laboratory. ("Changing Trends: A Brief History of the US Household Consumption of Energy, Water, Food, Beverages and Tobacco") The average single-family house climbed from 983 SF in 1950 to 1,500 SF in 1970, then 2,080 SF in 1990, and 2,266 SF in 2000.

Average household size was dropping during roughly that same period, from 3.67 members in 1940 to 2.62 in 2002, according to a study by Alex Wilson and Jessica Boehland, reported in the Journal of Industrial Ecology ("Small is Beautiful: U.S. House Size, Resource Use, and the Environment," Journal of Industrial Ecology, Winter/Spring 2005). This means that per-capita living space has increased even more over the past decades. A report from the Pacific Northwest National Laboratory ("Climate Change and the Long-Term Evolution of the U.S. Buildings Sector," April 2007) says that residential floor space in the U.S. is now on average about 800 SF per capita.

Can a Big House Be Green?

Architect Jason F. McLennan, CEO of the Cascadia Green Building Council and author of the Living Building Challenge (see my article "Living Buildings: Like LEED on Whole-Grain Natural Steroids") believes that house size is inextricably connected to the concept of "green building." Writing for Trim Tab ("The Righteous Small House: Challenging House Size and the Irresponsible American Dream," Trim Tab, January 2009), McLennan criticized the developers and builders of "grandiose homes" billed as "sustainable":

How, under any circumstances, can a 6,000-square-foot single family home be considered green? Something is terribly wrong with a system that ranks such a dwelling high on the green scale when it is intended to house only two to five people.

McLennan thinks the design and building communities, and American society at large, need to realign their thinking about housing to help consumers "seek saner, greener relationships with their homes." He proposes that the green building industry establish a "green square foot metric," a set of guidelines for house size per occupant.

The U.S. Green Building Council's LEED for Homes program and the NAHB National Green Building Program both reward smaller home sizes (see this comparison of the programs by the Vermont Green Home Alliance). NAHB penalizes (i.e., makes it hard to attain certification for) a house over 4,000 SF and rewards houses at increasing levels at 2,500 SF, 2,000 SF, 1,500 SF, and 1,000 SF.

The LEED for Homes program takes into account the number of bedrooms in a home. So, for a two-bedroom home, LEED penalizes a home over 2,060 SF and rewards a home under 950 SF. For a four-bedroom home, the standard penalizes houses over 3,820 SF and rewards houses under 1,770 SF.

McLennan's guidelines go further than these standards. First of all, he suggests setting a maximum house size of 4,400 SF, above which no house could gain sustainability certification. Then he proposes a size-per-person standard of 200 to 800 SF "depending on the depth of green design for the first three people in a household." A home with more than three people could add another 400 SF per person. So in the scenarios he proposes, a "green-sized" house for two occupants would be 400 to 1,200 SF, and 1,000 to 2,100 SF for four occupants.

Houston suburb

McLennan acknowledges that adhering to these guidelines could involve lifestyle compromises and self-imposed limits. He stresses that "the greenest solution is what people choose not to build." If people want to spend more money, the choice to encourage would be, not size, but investment in quality and design. (Photo: Houston suburb. Credit: Nelson Minar, CC BY-SA 2.0.)

Because McLennan's article came out in 2009, I got in touch and asked him whether he's seen any movement in the green building industry toward the guidelines he proposed. He told me that he hasn't seen "a ton of movement" in that direction. However, he and his colleagues have referenced these guidelines in the Living Building Challenge. He also tells me that

Lots of folks have read that article and refer to it on a professional level -- so I'm hopeful it's made a difference in terms of raising the issues... ultimately we just want to shift the market -- and that article was an attempt to get people to think about things from a completely different perspective... and I think it worked fairly well for that purpose.

I also asked him why he feels that the square-feet-per-person standard is better than LEED's square-feet-per-bedroom approach. He responded:

There is no one right way to encourage smaller houses... bedrooms is one way. But ultimately you can have one or two people with four bedrooms or more. And of course the other parts of a house could be grossly oversized. So I prefer SF per person as a way for us to think about limits... it comes back to the people. There is nothing wrong with a larger house if it has eight people living in it.

How Does House Size Impact the Environment?

In discussing the environmental benefits of small homes, most experts focus on house size and its relationship to energy savings. Wilson and Boehland write that

In general, the energy efficiency of a building envelope ... is a function of how well insulated it is, how airtight it is, the exposure of its glazed areas to solar gain, and its area. All else being equal, a house with more surface area will consume more energy for heating and cooling. Thus, a larger house -- or one that has more complex geometry --- will consume more energy.

Wilson and Boehland point out that the energy efficiency of a house is not merely a factor of its square footage, but can be affected by its ceiling height, the complexity of its geometry, and, of course, its energy efficiency. In general, though, their study finds that smaller homes use relatively less energy than large homes. They compared annual energy use of similarly-designed 1,500 SF versus 3,000 SF homes, and found that the smaller homes used 68-69 percent of the BTUs for cooling as the larger homes, and 48 percent of the BTUs for heating. Interestingly, even a poorly-insulated 1,500-SF house outperformed a well-insulated 3,000-SF house.

Michael Horowitz of solar company Sustainable Solutions, also a design and technology educator at U-32, a Vermont school ("Size Matters (a Lot): The Mistreatment of House Size in Green Home Rating Systems," draft paper, 2007), points to other environmental considerations that are affected by house size:

Water use, in landscaping and leakage in bathrooms, is also affected by size. Smaller homes with smaller roof areas create less runoff from gutter downspouts. As smaller homes require smaller volumes of paint, pest control chemicals, and cleaning products, size has an impact on health-threatening chemical use. The eventual dismantling or destruction of the home represents a smaller amount of construction debris.

EPA GHG emissions chartWhen investigating the environmental effects of any human activities, greenhouse gas (GHG) emissions inevitably emerge as a concern, and so it is with residential construction and house size. (EPA GHG Emissions Chart. Source: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009, EPA)

A data sheet from the U.S. Environmental Protection Agency (EPA) says that ("Buildings and Their Impact on the Environment: A Statistical Summary," April 22, 2009) there were nearly 128 million residential housing units in the U.S. in 2007. In 2005, buildings accounted for 38.9 percent of energy consumption in the country, and 53.7 percent of that was attributable to residential buildings. Residential buildings account for 20.8 percent of carbon dioxide emissions in the U.S.