Causality Factor Description: Commercial Square Footage
GOAL: To understand the trends and transitions in square footage since 1960, in both the residential and commercial sectors.
WHY: The biggest contributor to energy consumption in the Residential/Commercial sectors is environmental control, which is directly related to the size of the buildings being conditioned. For this reason, we have examined the trends and transitions in square footage and its relationship to population, number of buildings, and new construction since 1960.
MAJOR CONCLUSION: By and large, the biggest contributor to energy consumption in the residential / commercial sectors is actually new residential construction. This is exemplified by the square feet per new building calculation below which shows an distinctly upward trend, reflecting the fact that the average home size has doubled since 1960.
Notes -- 1. Some data was not available before 1980. Because of this, some of the graphs included below do not extend all the way back to 1960. It is noted, however, that the trends even since 1980 are distinctly upward, so we can safely make the assumption that trends since 1980 can be extended backward in time as well. 2. Beginning in 1995, commercial buildings on multi building facilities and parking garages were excluded from the commercial classification. This accounts for the sometimes odd changes in trends that occurs in 1995.
Trends (1960-2005) of Square Footage
It is important to first understand the overall trends in square footage. Below is a graph of total square footage in the US since 1960, divided up into the Residential and Commercial sectors. This is raw data from the Energy Efficiency and Renewable Energy division of the DOE. There are two trends to notice from this graph:
- Both the residential and commercial sectors have been steadily increasing the total square footage they occupy over the past several decades. (at a rate of 3.5% per year in Residential, and a rate of 1.0% per year in Commercial)
- The Residential Sector occupies approximately three times the square footage that Commercial does.
Since the Residential sector tends to dominate square footage in the US, it is important to break down the Residential trend for further examination. More specifically, the trends in spatial distribution around the United States were examined (regional classifications are depicted in the map below) and by home type.
Over the past four decades, the Southern region has both dominated the total square footage in the United States and has also had one of the largest rates of increase (22% since 1960). By total footage, the South is followed closely by the Midwest where homes tend to be larger overall (see below for more details). The Northeast has remained the most stable, probably because as one of the oldest parts of the country, most available space has already been used, leaving less room for additional space. The West has had the greatest rate of increase, but still lags behind the other regions in total square footage. 
In the Residential sector, square footage is often analyzed using a "square foot per housing unit" value. In order to better understand what those values mean, we must first look at how a "housing unit" is defined and how the total square footage values above are broken down. The types of housing units, defined by the Energy Efficiency and Renewable Energy division of the DOE, are: Single-family detached, Single-family attached, Mobile home, Multi-family (2-4 units), and Multi-family (>4 units). There are several trends to note:
- By far, the largest contributor is the single-family detached division. This is because this category has both the largest number of units and have the most square footage per unit (see Residential factors for more detail).
- Single-family attached units has been the fastest growing division. This trend is intuitive, as the US has seen a dramatic increase in condos being sold to retiring baby-boomers.
- Multi-family (2-4) units have been unstable, but not experiencing overall growth or decline.
Trends (1960-2000) of New Construction
Below are two graphs related to new construction in the US from 1960-2000. There are two trends to note: First is the obvious upward trend that both follow, with the notable exception of the early 1990's when the entire construction sector experienced a significant slowdown before picking back up. The second trend is the distinct correlation between residential and commercial construction rates. It is interesting to note that the residential sector leads by a significant margin in pure quantity of construction; residential construction comprises 75% of all new construction (in terms of square feet).
No calculations were done to create these graphs, it is raw data from the historical US Census Bureau Statistical Abstracts, section on Housing and Construction.
Parameters that Influence Square Footage
It is interesting to note that in the commercial sector, the most important parameter is the number of corporations, not the square footage per building as one might expect. The dramatic increase in number of corporations can be related directly back to the economic growth during the 1990's.  Note: A corporation is defined to be a non-farm, independently owned, profit-seeking organization by the US. Census Bureau.
As far as Residential sector parameters are concerned, the biggest driver is simply population with an 18% increase over the past fifteen years. Population is followed by square footage per housing unit with an 11% increase in the same time period, a.k.a. how large housing units are. This is not surprising because, as can be seen in the construction trends discussion above, new homes are getting larger and as a result, the overall square footage per housing unit is also increasing. This is a trend that has seen marked increase in recent years.
There are two main factors that have led to the dramatic increase in total commercial square footage seen in the first figure above. The first factor is that the total number of corporations (defined by the Census Bureau as non-farm, full time businesses) has been increasingly steadily. In fact, the number of corporations in the US has increased 82% in the past two decades; if that number is extrapolated back in time, that is a very large increase in corporate activity. The second factor is that the size of new commercial buildings has been increasing during the same time period. In fact, the square footage per commercial building has increased by nearly a thousand square feet.
No calculations were done to obtain the total number of US corporations and the data came from the IRS. The square footage per new building was calculated using data from the US Census Bureau Statistical Abstract, section on Housing and Construction, and is calculated by SqFt per Building = Total new square footage built per year / Total number of buildings constructed per year.
The most significant driving factor in Residential square footage is the increase in new home size; the average square feet per new home has increased rapidly and steadily in recent decades. The average new home is almost twice the size it was in 1960. Coupled with the decay of older homes, this dramatic increase in home size has increased residential energy consumption significantly. It is important to note that these numbers include all residential units, not only single-family houses, which means that the trends seen here are tempered by the inclusion of other smaller housing units, such as apartments and condos.
The square footage per new building was calculated using data from the US Census Bureau Statistical Abstract, section on Housing and Construction, and is calculated by SqFt per Building = Total new square footage built per year / Total number of buildings constructed per year.
The fact that new homes being constructed have been increasing in size is only part of the story, however. This trend can be broken down into square feet per household by both region and housing unit type. Surprisingly, the largest average home size is found in the Midwest, with the South also contributing significantly to the average home size. The Midwestern trend is probably due to the increase in suburban lifestyle in this region.  Another trend to notice is the dip in the 1980's, which is an after-effect of the energy crisis in the 1970's, during which people became temporarily more energy conscious. It is also interesting to note that of the four regions, the Northeast and Midwest tend to follow each other closely, as compared to the South and West which also follow each other closely. This is probably indicative of how and when the four regions developed - the Midwest developed in a similar economic direction as the Northeast. The same can be said of the South and West. Finally, it appears that when the four regions are normalized to 1990, they have all had a fairly slow and steady upward trend in overall housing size.
These graphs show the square feet / housing unit broken down by unit type, with single-family homes (both attached and detached) far out-sizing the other housing types. This makes intuitive sense since mobile and multi-family units tend to be inhabited by people of a lower economic status, they have less money to spend on extraneous housing space. The trend here is an upward one for all of the housing types.
Personal Contributions to total Square Footage
There are two areas examined here: commercial and residential trends. Since it is difficult for consumers to have a direct influence over the number of corporations (which is not a number we necessarily want to limit) or over corporate floor space, the best way for American citizens to reduce their energy consumption due to square footage is to focus on the Residential sector. This makes sense because Residential construction is three times the amount in total square feet constructed per year, and it is also the area easiest to have a direct impact on. The simplest way to change the upward trend is simply to be more conservative in new construction, reducing the square feet per new building. The McMansion fashion has caused the average new home to double in size, which is the biggest factor in overall square footage calculations. If Americans want to change their energy consumption, reducing this is the best place to start.
- Energy Efficiency and Renewable Energy - Indicators of Energy Intensity
- Census Bureau - Statistical Abstract
- IRS - Integrated Business Data
- Census Bureau - Population Estimates
- Energy Information Association - Annual Energy Review