The girth of the average American house grew precipitously in recent decades, with square footages climbing from an average of 1,500 in 1973 to 2,460 in 2007.  But that trend may finally be on the downswing -- or at least plateauing -- according to the latest AIA quarterly Home Design Trends Survey, which tracks business conditions inside 500 residential architecture firms.

As recently as 2006, the number of architects reporting increases in the sizes of the homes they were designing was nearly double the number reporting decreases.  But by 2007, that trend had reversed, with more architects noting downsizing over expansion in floor plan size.  In the most recent AIA survey for the first quarter of 2008, the share of architects reporting a decrease in house sizes was more than double the number citing increases (34 percent versus 16 percent).

"The recent weakness in the housing market forces households to be more sensitive to housing affordability concerns," AIA chief economist Kermit Baker said in a release. "Coupled with rising energy costs, this encourages many to rethink their overall space needs.  While smaller homes may be a short-term response to economic conditions, there are signs that we may be at the beginning of a longer cycle where house sizes stabilize or even decline."

With the release of the AIA findings, some of the trends prophesied in an NAHB "Home of the Future" study released last year appear to have come true.  That study, which polled 500 architects, designers, manufacturers and marketing experts, anticipated an end to housing's 30-year anatomical growth spurt, forecasting that average home sizes would level off at around 2,400 square feet by the year 2015. "We don't think the size will rise anymore," NAHB vice president of research Gopal Ahluwalia told an audience at the 2007 International Builders' Show in Orlando.

However, one crystal ball prediction appears not to have come to fruition.  Respondents in last year's NAHB study anticipated that what homes lost in the way of lineal square feet they would recoup as volume space.  But fast forward to 2008 and skyrocketing energy prices appear to have put the kibosh on that notion.  Whereas more than half of residential architects in AIA's 2005 Home Design Trends survey reported an increase in volume features such as cathedral ceilings and two-story foyers, only 28 percent reported volume increases in the most recent study. 

Lot sizes held steady in the AIA study in a year-over-year comparison, with only 7 percent of respondents reporting increased acreage.