I’ve been noticing that older houses in my Seattle-area neighborhood are being steadily replaced by much larger mansion-sized structures—one of which is large enough to be an orphanage. Apparently this is a national trend: the size of new single-family homes has more than doubled since the 1940s (from 1,100 to 2,340 sq.ft.), according to a recent article in the Journal of Industrial Ecology (see full pdf here). Combining this with the trend towards smaller households (from 3.67 to 2.62 members), authors Wilson and Boehland find that:

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 has several environmental implications.  Larger houses not only use more building materials, but may also consume proportionally more.  Larger houses that include higher ceilings, complex designs such as extra wings, and other features may mean that material use increases proportionally faster than square-footage.

  • And building out has more impacts per square foot than building up because the increased impervious footprint generates more storm water runoff, taxing sewer capacity.

    Not surprisingly, big houses also require more energy to heat and cool. Good insulation and green building techniques can only do so much for conservation.  When the authors calculated heating and cooling costs for a small, poorly insulated house and a well insulated house twice as large, they found the small house still used almost a third less energy.  So size really does matter, as Clark has also bloggedabout.

    What has caused the trend?  Wilson and Boehland cite several factors.  Some zoning laws and development covenants mandate minimum house sizes (but some now also mandate maximums).  Mortgages for new houses often specify a minimum ratio of house value to land value. And until 1998, tax laws required home sellers to buy a house of equal or greater value unless they wanted to pay capital gains taxes on the appreciated value of their old house.

    Wilson and Boehland also suggest that the notion of "bigger is better" may be inflating house sizes (see Alan’s post on up-sizing the American dream).  But a big house can also be lifeless: quantity without quality.  Instead of adding extra rooms, new home builders could invest in the details that give houses their charm (moldings, built in cabinets, granite countertops) and spend more for green details (better insulation, water-saving devices, sustainable materials).  They’d save money on energy bills and reduce their environmental impact.

    Personally, I’d rather spend my home time reading in a bay window seat than cleaning an extra 600 square feet of house.