Knock, knock. Who’s there? And how many?

I ran across another great article on Life Edited, this time on household size.

All along I have touted laneway homes as a good method to increase the densification of neighbourhoods without changing their character.  These houses, by nature of their small size, will only house one or two people each.  What about the housing density of the rest of the neighbourhood?

Not this kind of housing density.

We tend to frame the density issue in terms of housing size, because it’s easy to understand that big homes, as a rule, reduce overall density. But there is something else, just as important as housing size, that must be factored in to understand how density works, and that is household size.

The article quotes a paper in the online journal Population and Environment.  Looking at the population/housing ratio in the past 400 years,

the number of households grew faster than population size in every country and every time period. These findings suggest accommodating housing may continue to pose one of the greatest environmental challenges of the twenty-first century because the impacts of increased housing present a threat to sustainability even when population growth slows.

There are fewer people being born per capita, true, but

Progress made in curbing population growth, however, has not translated into reducing human
consumption of natural resources and impact on the environment.

Yikes!  Why?  Of course there are lots of reasons, and it’s not just because people are building larger homes (McMansions) for their smaller families.  People are also moving out of the family home at an earlier age.  The trend during the recent economic downturn for people to move back in with their parents after college is an anomaly, and probably will not be continued after the economy picks up again.  Also elderly people stay in their own homes longer rather than moving in with their families.  Plus they remain in their old family homes longer rather than moving to smaller ones.  There are other factors as well

The rising incidence of divorce also encourages increased household numbers. In the United
States, 15 % of all households had divorced heads in 2000 …. Although remarriage is common, the relatively high percentage of divorced households persists, and divorced households are 27–41 % smaller than married households

And that means?

From a more simplistic perspective, declining household sizes, from over 5 to approximately 2.5, will mean approximately twice as many houses will be needed per capita in any areas of the world yet to undergo the shift in household size.

Assuming that each of the additional households occupies a 210 m2 house (the average US
house size in 2002) (National Association of Home Builders 2004), then an additional
185,800 km2 of housing area would be required. This estimate may be conservative because land
area for household-related infrastructure (e.g., roads, yards, and retail) can require 2–4 times as
much land as the actual land used for the home …. Each of those houses would demand more household products and have lower efficiency of resource use per person because fewer people share goods and services in smaller households.

That’s why urban sprawl — taking more land to build more houses — will not solve all the problem.

One small caveat by Life Edited shows a glimmer of light in the tunnel of doom:

As a small space design blog, we’d be remiss if we didn’t mention that the amount of sprawl (i.e. the 72K sq miles) they calculate is based on a house size of 2509 sq ft–McMansions for all.

So smaller houses will help the problem well into the future.  And they give us a couple of options,

1. Let things remain the same. Encroach on undeveloped lands and deplete all natural resources until the planet’s homeostatic environmental mechanisms are irrevocably destroyed.

2. Reverse demographic shifts away from industrialization, the desire for privacy, divorce and so forth.

3. Rethink housing. Adjust housing style to meet demographic shifts. Have smaller, more efficient houses with shared amenities. Creatively subdivide existing housing. Mitigate sprawl by keeping density high, even outside of major metropolises, permitting walk/bike/public transportation-friendly living.

That last choice seems the best to me.