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U.S. House Size, Resource Use, and the Environment

Article from MIT Journal of Industrial Ecology, Winter/Spring 2005 issue.
Read/download the full article here.

As house size increases, resource use in buildings goes up, more land is occupied, increased impermeable surface results in more stormwater runoff, construction costs rise, and energy consumption increases. In new, single-family houses constructed in the United States, living area per family member has increased by a factor of 3 since the 1950s. This journal article examines some of the trends in single-family house building in the United States and provides recommendations for downsizing houses to improve quality and resource efficiency. By Alex Wilson and Jessica Boehland
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Since 1950, the average size of new single-family houses in the United States has more than doubled, even as the average family size has steadily shrunk. More area (square footage) per family member is being used than ever before, and projections are that the trend will continue. As house size increases, so too do the environmental impacts associated with buildings and development: resource consumption increases, the land area affected by development grows, stormwater runoff increases as impermeable surface area increases, and energy use rises. In addition to carrying larger environmental burdens, larger houses cost more to build and operate. For single-family houses, "small is beautiful" in terms of environmental performance.

Because single-family, detached houses account for 63% of total dwelling units in the United States (U.S. Census Bureau, 2001), this study focuses solely on single-family houses. A broader study that examined single-family attached houses, multifamily buildings, and mobile homes would produce somewhat different and probably less dramatic results.

Demographics vs. House Size

The U.S. Census Bureau has been collecting detailed information on household size since 1940 and tracking certain characteristics of houses since 1963. Data on houses were collected by the U.S. Department of Housing and Urban Development and other agencies from 1940 to 1963. Average household size in the United States has dropped steadily from 3.67 members in 1940 to 2.62 in 2002. The average size of new houses increased from about 1,100 ft2 (100 m2) in the 1940s and 1950s to 2,340 ft2 (217 m2) in 2002. Factoring together the family size and house size statistics, we find that in 1950 houses were built with about 290 square feet (27 m2) per family member, whereas in 2003 houses provided 893 square feet (83 m2) per family member (NAHB 2003) -- a factor of 3 increase.

Other trends in American single-family housing have been similar. In 1967, for example, 48% of new single-family houses had garages for two or more cars; by 2002, that figure had jumped to 82%. In 1975, 20% of new single-family houses had 2.5 or more bathrooms; by 2002, that figure had increased to 55%. In 1975, 46% of new houses had central air conditioning; by 2002, 87% had it.

Resource Consumption

Larger houses consume more resources -- both in construction and during operation. The U.S. National Association of Home Builders (NAHB) estimates the materials used in building a 2,082-square-foot (193-m2) single-family house to include 13,837 board-feet of framing lumber, 11,550 square feet (1,073 m2) of sheathing, and 16.92 tons (15,350 kg) of concrete. One would expect that, relative to material use, there would be an economy of scale as house size increased -- that material use per unit area of floor area would drop as floor area increased.

But that is not necessarily the case, according to Gopal Ahluwalia, the director of research at NAHB. Although NAHB has not compiled data on material use as a function of house size, Ahluwalia believes that, because larger houses tend to have taller ceilings and more features, larger houses may actually consume proportionally more materials. He estimates that a new 5,000-square-foot house will consume three times as much material as the 2,082-square-foot house NAHB has modeled, even though its square footage is only 2.4 times as large. Even if Ahluwalia's intuition is not correct and larger houses are more material-efficient per unit area of floor, the higher ceilings and added features in large houses may mean that material use efficiency improvements with increased floor area of a house are not proportionate -- that is, that the increased material efficiency one would expect from purely geometrical calculations is not realized.

The use of lumber, structural panels, and nonstructural panels in new houses from 1950 through 1992, along with figures for total wood use calculated from these data, are presented in table 2 below. As would be expected, total wood use in houses has increased steadily between 1950 and 1992, as houses have grown in size. But when we examine total wood use per unit of floor area, we find that it dropped between 1950 and 1970 -- perhaps due to the substitution of plywood sheathing for board sheathing and the introduction of more wood-efficient roof trusses. Then, around 1970, wood use per square foot of floor area began to increase again, and by 1992 it was up about 12% from the low point. Exactly why this is occurring is not clear; it could result from an increasing use of 2×6s instead of 2×4s1 for wall framing, or a shift to more complex geometries.

In general, the energy efficiency of a building envelope (i.e., the structural elements that enclose a building, including the walls, roofs, and foundations) 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.

A house's smaller square footage does not always mean a comparable reduction in surface area. If one reduces the total size of a house but breaks it into smaller, separate wings and more complex geometry, for example, as is sometimes done in custom houses, one may not gain much in the way of energy savings compared to the large box. Along with the greater surface area increasing heat loss and unwanted heat gain, larger houses also generally require longer runs for ducting and hot water pipes. Losses in conveyance of warm air, chilled air, and hot water can be significant.

Quantity vs. Quality

With single-family houses, the notion that bigger is better has been a leading driver of the real estate industry. Large houses are a status symbol. Even retirement homes built for "empty-nesters" (couples whose children have left home) are usually a step up in terms of size. Virtually all segments of the American home-buying market are buying the largest houses they can afford.

Designer-builder John Abrams of the South Mountain Company in West Tisbury, Mass., describes three factors that are driving the popularity of large houses: "First, with less of a sense of community and public life in our culture, the home becomes a fortress which needs to contain everything we need, including multiple forms of entertainment, rather than basic shelter; second, the building industry has been selling 'big is better' and the message has been heard; and third, diminishing craft and design generosity has resulted in sterile homes -- people mistakenly think that what's missing is grandeur: more space."

This status quo is being questioned today. Homebuyers are becoming less interested in size than they are in quality. Sarah Susanka's book The Not So Big House (1998), which emphasizes a very different approach to house design -- one focused on quality, not quantity -- is selling extremely well. According to Taunton Press, over 360,000 copies have been sold. Two of Susanka's subsequent books also continue to sell well: Over 240,000 copies of Creating the Not So Big House (2002) and 50,000 copies of Not So Big Solutions for Your Home (2002) have been sold. A residential architect in North Carolina, Susanka argues for space-efficient houses with spaces that will be used. For example, she suggests eliminating the formal dining room in favor of a larger kitchen that provides both dining space and some informal living space.

The South Mountain Company has been emphasizing space-efficient houses since its launch nearly 30 years ago. In addition to providing open-plan living/dining/kitchen areas, the company suggests providing built-in furnishings and storage spaces, eliminating single-use hallways, designing multiple uses into rooms, and utilizing often-wasted attic and low-roof space.

Legal and Regulatory Issues with Building Small

Zoning regulations, restrictive covenants (i.e., provisions in the deed for the property that restrict the way the property may be used by the owner) and design standards for specific subdivisions, and even mortgage banking requirements2 can significantly limit options for creating small, space-efficient, single-family houses. Some municipalities establish strict limits on how small a house can be. Though less common than in the past (due in part to lawsuits that have challenged their constitutionality), such regulations still exist. In the suburbs around Atlanta, Ga., for example, Fulton County specifies a minimum heated floor area of houses in most of its zoning districts. For single-story houses, these minima range from 850 to 1,800 square feet (79-167 m2); for two-story houses, they range from 1,100 to 2,000 square feet (102-186 m2).

Far more common than minimum house size regulations in municipal zoning ordinances are restrictive covenants established by developers for specific, privately controlled subdivisions. In the La Marche Place neighborhood in the 3,400-acre (1,400-ha) Wooded Hills subdivision in Little Rock, Ark., for example, single-level houses must be at least 2,600 square feet (242 m2) and multilevel houses at least 3,000 square feet (279 m2). In the Spring Glen subdivision in Medina County, Ohio, the minimum heated square footage of houses (exclusive of garages, finished basements, porches, etc.) ranges from 1,800 to 2,600 square feet (167-242 m2), with a provision for reducing the square footage by up to 10% if the developer deems that "the design is unusually good and is or will be compatible with other houses in the development."

Mortgage bankers can also in effect specify minimum house size for new houses by mandating ratios of house value to land value. Secondary mortgage markets often have a rule of thumb that the lot should not be worth more than 30% of the total value of the real estate. Thus, on an expensive lot, homeowners are required to build expensive, and therefore often large, houses. Appraisals (which assess the value of the a house for financial or taxation purposes) for small houses also run into difficulty when all the houses in a particular area are very large and the appraiser cannot find small comparable houses. This issue does not apply at the high end of the real estate market, where land values commonly exceed house values.

Examples also exist of both zoning regulations and restrictive covenants on subdivisions that specify maximum house size. Many municipalities effectively limit the footprints of houses on small lots by specifying the maximum coverage of the lot. This restriction is generally governed by stormwater concerns, but particularly with small infill lots, it can have a big impact on house size. Cupertino, Calif., goes much further by restricting house floor area to a maximum size of 6,500 square feet (604m2) -- less in areas of significant slope or smaller lots (Cupertino Municipal Code 1999).

Santa Cruz County in California and several communities in Chicago, Illinois, USA suburbs also have maximum house size regulations. In the Chicago area the regulations are addressing a trend referred to as mansionization, in which houses are often designed to fill the maximum available footprint of a lot -- overwhelming the neighborhood scale.

In the environmentally focused Dewees Island subdivision in South Carolina, maximum house size has been established by covenant at 5,000 square feet (465 m2). Given that this is a luxury development, with most 2-acre sites selling in the $400,000 range, but some as high as $850,000, this restriction on house size is highly unusual. So is the fact that there are no minimum floor area or footprint requirements. Developer John Knott suspects that they have lost a few sales because of these standards, but in general he thinks that property owners feel relief at the maximum size limit -- they don't have to "keep up with the Joneses." The average-sized house at Dewees is 2,600 to 2,700 square feet (242-251 m2), with the smallest just 1,200 square feet (111 m2).

Another influence on house size in the United States has long been capital gains tax policy. Until recently, when an American family sold a house it had to buy a new house of equal or greater value within 2 years to avoid capital gains tax on the appreciated value of the house that was sold. That policy often resulted in people moving into larger houses, especially empty-nesters moving into areas with lower real estate values. Since that policy changed in 1998, U.S. citizens are no longer taxed for capital gains on the first $250,000 value ($500,000 for a couple) for a primary residence, so the incentive for moving up into larger houses to avoid capital gains taxes is gone or significantly reduced in most cases.

Selling the Concept

Even without any regulatory or financing impediments to building compact houses, convincing others of their benefits can be challenging.

Clients often have preconceived notions of how large a house they need, often because a friend's house of that size seems to have the features that the client wants. A different understanding may be reached if the clients focus on their housing needs and expectations. Visiting high-quality, compact houses may also influence their views. It may also be possible to convince clients that, by keeping the square footage down, they can end up with a higher quality house.

Rather than using up the budget to create the largest, most impressive house possible, many designers today recommend creating smaller houses with a higher level of finish quality and added amenities. "A house that favors quality of design over quantity of space satisfies people with big dreams and not so big budgets far more than a house with those characteristics in reverse," says Susanka. She argues that a good house designer should suggest to clients that, for a given budget, they reduce square footage to allow high-quality detailing. Fine carpentry detailing, granite countertops, hardwood floors, labor-intensive but soulful salvage materials, and quality architecture can be far more impressive than sheer size.

On the regulatory side, remaining zoning ordinances that mandate large houses should be eliminated, and zoning regulations should be revised to prohibit or discourage design standards or covenants in private developments that mandate large houses. Restrictions in private developments that specify maximum dwelling size should not be prohibited or discouraged. Rather, regulatory incentives should be developed that encourage such restrictions.

Final Thoughts

A great deal of attention is paid to material selection and energy detailing in creating environmentally friendly ("green") houses. Designers, builders, or owners of these houses seek out recycled-content building materials, low embodied- energy materials, or natural materials. Advanced framing techniques reduce wood use. Well-insulated walls and ceilings, high-performance glazings, and efficient equipment reduce energy consumption. But far too often, the more important consideration of size is overlooked.

A 1,500-square-foot (141-m2) house with mediocre energy-performance standards (R-13 walls and R-19 ceilings) will use far less energy for heating and cooling than a 3,000-squarefoot (28-m2) house of comparable geometry with much better energy detailing (R-19 walls and R-30 ceilings). Downsizing a conventionally framed house by 25% should save significantly more wood than substituting the most wood-efficient advanced framing techniques (24"-on-center studs, single top-plates, two-stud corners, elimination of cripple studs at windows, etc.) for that house. And it is easier to reduce the embodied energy of a house by making the house smaller than by searching for low embodied- energy materials.

In considering space requirements in houses, storage requirements should be considered. Anecdotal observations show that Americans have more belongings than used to be the case. Thus, spaces need to be designed not only for the people using those houses, but also for the many belongings those homeowners own. A shift toward smaller houses may also necessitate some degree of change regarding possessions. This issue has not been addressed in this article.

Building small is not easy. To make small houses work well requires understanding the needs of homeowners and then fulfilling those needs with careful design. Simply using off-the-shelf house designs may not adequately account for the specific needs of a family. Fortunately, a number of excellent resources on compact house design are available, some of which include floor plans and elevations. To ensure success with small, resource-efficient houses, however, builders should involve a designer, preferably one with experience in compact house design. And both builders and designers should spend enough time with clients to adequately explain the benefits of smaller houses.

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For references and illustrations, download this article in PDF format.

This article has been reprinted courtesy of the Journal for Industrial Ecology. It was first published in the journal's Winter/Spring 2005 issue.

posted by Jason English @ 10:00 AM