imo the study shows that the more separate living units there are , the more energy is being used . what the study did not address is the enormous spread of suburbs and the increase of house sizes .
if people live ever farther from their place of work , more energy will be needed to get them there and back . similarly , the bigger the houses get , the more energy it'll cost to build and maintain them .
india and china are still good examples that demonstrate that large family units living under one roof use less energy . of course , indian and chinese people now watch TV and see how the people in the developed world are living , and they are beginning to like the idea of having more living space .
imo the city of toronto is a good example of how people from india - just to give an example - that can afford it , are having really enormous houses built . i doubt that they can really make use of all the living space , but it gives them the satisfaction of being able to show that they HAVE ARRIVED .
i'd compare that to the 1950's and 1960's when many immigrants arrived in canada from europe . often the first major purchase was a LARGE used car . pictures would be taken and sent home to the families in europe to show how RICH they were . they may have been living in a basement or an attic room ; of course , they wouldn't send a picture of that home to the family .
dutch architects and builders have come up with interesting ways of building (row)houses with a very small footprint . since they have a small country with many immigrants , they had to find ways of putting ever more people into the available space .
in canada and the USA we have plenty of space and think nothing of using up more and more land for housing . in southern ontario there is now some movement by government and developers to come to grips with the ungainly spread of suburbs that are eating up ever more farm land .
modern city architects are suggesting that we should not just "build out" - using up more land - but build up . they are not suggesting that skyscrapers are the solution but that "stacked" housing , such as eight or twelve individual "living spaces" can be combined into a unit . it would give families the privacy they desire , while taking up less land and require less energy to build and maintain .
(i have to admit that we live in a small bungalow that was built for us in the early sixties on a city lot that nowadays would give space for at least a fouplex ) .
getting more bang for buck in building accomodation (houses , condos , apartments) is really not a difficult thing to achieve , but will require us (particularly in north-america) to accept some changes in life style .
looking at housing in old european cities and even a city such as quebec city , shows us that we can live with a SMALLER FOOTPRINT - if we are willing to !
hbg
STREETSCENE IN QUEBEC CITY - many of these houses were built more than 200 years ago - notice the density of housing
DUTCH CUBEHOUSES
We can't trust those buggers 
So why not blame divorce 