Just under the title, "Greener Pastures?", they state that the comparison is based on average household with income and family size etc standardized.

Can detached housing in the suburbs be made efficient enough, or must everyone move into a crowded urban environment?

In my view, the suburbs are never going to look good by comparison. Yes, it's possible they can be made to look ok by comparison with currently existing multi-family units, but remember that new large units are going to be redesigned also as time goes on to be very efficient.

On a personal note, I live in a high-rise condo with my own furnace in the unit. My neighbours are so profligate with energy use that even though I live in Canada, I don't need to run my furnace at all except on those half-dozen or so ulta deep-freeze nights that come every winter. So, in a dense urban setting your neighbour's waste can be your gain. If my neighbours ever turn green, it's going to cost me!

What does "crowded" mean?

Seriously, what is a "crowded" environment?

If you think about it, to most Americans it means "a place that is hard to drive."

Did you go to a residential college? Was it "crowded"? You probably never felt crowded. In fact, if you were like me, you probably felt a need to stick close to the campus, where all the action was. This is because residential college campuses are, generally, no-car pedestrian environments. Even though most colleges have lots of greenery and open space, they are typically quite "dense" due to lots of dormitory residences.

Unfortunately, I don't know of a single example of a no-car pedestrian urban environment in the US, not even Manhattan. However, they are quite common in the rest of the world.

Another reason people feel "crowded" is because they live close to people they would rather not live with. However, if they live close to people like them (think of a college campus or the Upper West Side of Manhattan) then it doesn't feel "crowded" anymore, does it?

The last significant reason that people feel "crowded" is because they are in a multifamily structure with inadequate sound insulation. This is merely shoddy construction.

One thing to think about, regarding these statistics, is that they are from Atlanta. The multifamily dwellers generally live side-by-side the single family detached dwellers in automobile suburbs. The real gains are had when you get multifamily dwellings in a pedestrian/subway/train environment. Subways/trains use about 10% of the energy per person/mile compared to cars, and also trips are shorter.

Also, you can have SFD dwellings in a dense urban environment. Think of Greenwich Village. Tokyo's first apartment building was constructed in the 1920s. Before then, the city consisted of very dense single-family residences, often on plots of 500 square feet or less. I have been in some pre-1930 neighborhoods, and they are quite lovely. Because they are too dense for cars (the streets are simply too narrow to drive, and are really more like walkways), they are "uncrowded"!

I think all they have done here is shown that more wealthy people use more energy, which if not obvious, has already been shown by various studies.

There is also the issue of how well the house is insulated and how it is heated. Those fators have to be included. It is much easier to put a ground source heat pump into a detached home than a semi or townhome because of the more land available.

Also, appartments are much less energy efficient in their heat use. Many older appartments have no insulation at all, just brick and concrete with poor single glazed windows.

Thus the comparison is misleading.