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Reverse Zone, weblog on urban planning, sustainability, and technology.

Martin Laplante

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Tue, 15 May 2007

Which is Greener, Houses or Apartments?

Which one uses up more energy per square foot, a single detached house, or an apartment in a large building?

That should be easy: most of the walls of your apartments are interior walls, only one surface is exposed to exterior temperatures, as opposed to six surfaces in a single detached house. Plus you have economies of scale: you can insulate the heck out of that one surface and two windows, and the entire building can share the cost of the most efficient heating and cooling technology available and make the investment worthwhile.

You would think that apartments consume a lot less energy per square foot than houses. You would be wrong. According to the U.S. Energy Information Administration, Office of Energy Markets and End Use, apartments consume more energy per square foot than even single detached houses. An average single-family detached house consumes 44,700 BTU per square foot, while an apartment in a building with 5 or more units consumes 48,500 BTU per square foot.

Air conditioning a 3-bedroom unit consumes 4,300 BTU/ft2 in a house and 7,600 BTU/ft2 in an apartment. Heating does takes less energy in apartments, but the total energy use is higher. Is it the elevators? Is it the hall and lobby lights left on all night? I don't know. In another article I wrote last year, it turns out that in most densities, apartment dwellers drive more than house dwellers.

So, seriously, why are companies like Tridel building nothing but apartment buildings in their "Green Communities" repertoire?


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