Perhaps you misunderstood what I meant by “looking under the lamppost”. The increase in square footage is typically invoked as a response to the increases in share of household spending going to housing. Implicitly or explicitly, it’s “but look how much more people are getting for the additional money they’re spending”.

My point was that increased square footage doesn’t necessarily mean increased utility (which tends to correlate better, although still imperfectly, with number of rooms). Increase square footage also doesn’t correlate all that well with increased construction cost. All it correlates with is spending more money, which is something we already knew.

At 21, I posted census data showing a significant increase between 1984 and 2006 in the share of household spending going to housing. So the phenomenon does not seem to be just an artifact of looking at square footage.

I live in a house whose utility would probably be improved if it were several hundred square feet smaller, because the rooms that are larger than they need to be cost more to furnish, heat and cool; they also make it harder to clean and lead to unpleasant furniture arrangements. I’ve seen plenty of mcmansions where a normal house worth of furniture is just lost in the big rooms, and people turn out to live in a few reasonably-sized corners. Unfortunately, most such houses are built (structurally and architecturally) in ways that make it impossible to rejigger the space into more livable condition.

That yields an 11% increase to get the 2005 1,758 sp ft.

That is over 20 years or about a 0.5% growth rate.

This implies that the increase over 60 years from 1945 would be about a third as compared to the Builders Association statement that new home sizes doubled.

But the Census housing survey has the median size of the existing housing stock at 1,768 sq ft.==
this is 72% of the data you linked to.

I did not check to see how far back the Census housing survey goes back, but you might want to check that data.

The median home in the US in 2005 was built in 1973.

Because of this using the size of new homes is using data on the marginal home rather then on the average home.

You need to go to the American Housing Survey at Census to get the data you want.

For example, single family detached homes only account for around 62% of the housing stock.

Good try at cutting a deal, but you’re never going to make it as a real estate broker unless you tell the buyer the house is BIGGER than reported and tell the mortgage company that the buyer’s income is BIGGER than reported.

These arguments became a lot less meaningful to me when I started looking carefully at the time use statistics. Across all adults in the USA, the average work hours per day is 3.75 hours, the average leisure is 5.09 and of that 5.09, 2.58 is spent watching TV. Big house, flat income, who cares? What people really seem to want is a good TV show.

Changes in school costs and the legal framework in which schools operate made lving in a uniformly high-income area much more valuable.

4. The tradeoff between longer commutes and larger houses got more favorable in a period of suburbanization and cheap oil.

But the evidence is pretty clear that both facts are true, partly because housing costs have declined, but mostly because people are choosing to spend more on housing.

Why people choose to devote to more of their incomes to housing is the puzzle. Presumably, it’s some mix of:

1. Regulations have made it more difficult too build smaller homes.

2. The specialized mortgage-lending system makes it easier to finance housing purchases than alternative forms of consumption. (Yes, this was probably at least as true 30 years ago, but as more and more consumption is debt-driven, ease of financing becomes more important.)

3. Houses becoming more attractive as an investment as well as consumption good. Especially true in the bubble period, obviosuly, but probably a longer-term trend.

Untangling these explanations—and whatever others I’m not thinking of—is an interesting question. But John Q.’s approach, of trying to find reasons why housing consumption has not increased as much as it seems to have, is pretty clearly barking up the wrong tree.