How Urban Development Impacts Energy Retrofit Programs

I grew up in Los Angeles, described as a true ‘post-modern’ city because it lacks a recognizable center. Sprawling in size, it developed as a cluster of independent destinations connected by a network of transportation lines. This is partially why the symmetric pattern of Twin Cities neighborhoods, while more common across the Midwest, is notable to me. A much older settlement, the Minneapolis-St Paul axis forms a central core, and the suburbs radiate outward in tiers. The first ring suburbs were products of the 1950’s, built to house returning vets, their families, and their cars. The second ring suburbs of the late 1970’s and 1980’s grew in part when social influences caused a number of residents to leave the Twin Cities urban core, looking for green grass and better schools. And the recent boom during the 2000’s, driven largely by economics, meant that people had to look to the exurbs for moderately priced housing.

Thanks to the blog Getting Around Minneapolis for putting together a great series of maps that illustrate this point, including the one below for 2007 population density by census tract (est.).



The interesting implication for retrofit programs is that these different cities have distinct housing types, built to the code and style of that era. These housing types will often differ in which retrofit measures should be a high-priority. For example, older homes were built without any insulation, and a high percentage still need this upgrade (we estimate that 25 percent of Minneapolis homes lack wall insulation). Newer homes were built with a higher level of insulation, so for them, a focus on efficient appliances, refrigerator recycling, and reducing plug load losses is often a better focus. These two things have different implications for program design and follow through.

To help understand these issues, we put together some graphs of housing builds by date and type of house. They show the notable difference in housing stock between central Minneapolis and one of its second tier suburbs, Apple Valley. The data were compiled from the cities’ assessor databases and span 1900 through 2009. 





In Minneapolis, three-quarters of all single family homes were built before World War II. (The spike in 1900 refers to all the homes built before the 20th century, which total 4,667.) These homes are dominated by single story and bungalow homes, which here include everything from 1¼ to 1¾ stories. Bungalow style homes are unique from a retrofit perspective because their attic structure is more expensive to insulate compared to full one- or two-story homes. New home builds in Minneapolis trail off by the early 1960’s, when the city was essentially built out. 

This is when Apple Valley got started. Developers started converting farmland to new housing in the 1960’s, leading to the area’s incorporation as a city in 1974. Like Minneapolis, there are still a number of single story homes, but the ‘split level’ home style now emerges, owing to the popular ranch style construction of that time. Two story homes gained popularity in the 1980’s when developers turned towards maximizing square footage for property value, and by the mid-1990’s, two-story homes were essentially all that was built.

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Photo credit:

  by  Transguyjay