1 

Analysis of Housing Square Footage Estimates 

 Reported by the American Housing Survey 

and the Survey Of Construction 

Angela L. Delano 

U.S. Census Bureau 

4600 Silver Hill Road, Washington DC 20233 

Angela.Lynn.Delano@census.gov

Disclaimer: Any views expressed on (statistical, methodological, technical, or operational) issues are those of the 

author(s) and not necessarily those of the U.S. Census Bureau. 

Introduction 

Government agencies, policy analysts, financial institutions, and manufacturers, to name a few, use data collected by 

the U.S. Census Bureau. This data helps measure and evaluate size, composition, and change occurring within the 

inventory of residential housing units available in the United States. One important measurement associated with 

this inventory relates to housing unit size. The size, or square footage, of a housing unit and the corresponding 

change of this measurement over time plays an important role in costs associated with buying residential homes 

(Sirmans & Macpherson, 2003) and heating residential homes (Energy Information Administration, 2012). Up until 

now there have been no studies analyzing housing square footage estimates reported by surveys conducted by U.S. 

Census Bureau. 

This paper will examine housing square footage estimates reported by two U.S. Census Bureau conducted surveys – 

the American Housing Survey (AHS) and the Survey of Construction (SOC). These surveys are funded either in full 

or part by the Department of Housing and Urban Development (HUD). First, I will present a brief overview of the 

surveys. Next, I will discuss methods used to analyze housing square footage estimates reported by the surveys. 

Discussion of housing square footage estimates reported by the surveys will follow. Next, I will discuss issues 

associated with the collection and conversion of housing square footage estimates. These issues include differences 

between the surveys regarding sample sizes, survey designs, and square footage definitions. In addition, discussion 

of conversion issues specifically related to the SOC will also take place. Together these issues may suggest reasons 

for housing square footage differences reported by the AHS and the SOC. Finally, I will discuss updated square 

footage analysis results and offer proposed enhancements to the collection of housing square footage estimates by 

the AHS and the SOC. 

 

AHS Background 

AHS Survey

The AHS is the most comprehensive national housing survey in the U.S. The survey provides national and regional 

data on a wealth of topics related to the quality of U.S. housing. Topics covered by the survey include basic house 

characteristics (such as the number of bedrooms, bathrooms, and square footage), data on physical conditions, 

occupant demographics, and financial data such as home improvements, costs, and mortgages to name a few. The 

survey is sponsored by HUD and conducted by the U.S. Census Bureau. 

AHS Design

The AHS is a longitudinal housing unit survey conducted biennially between May and September of odd-numbered 

years. The most recent AHS took place in 2011. The 2011 AHS consisted of a national sample of housing units and 

a supplemental sample of housing units selected from predefined metropolitan areas. 
2 

AHS Sample

Housing units selected for the AHS represent a cross section of all U.S. housing. Updates to the survey sample occur 

prior to each survey by adding newly constructed housing units and units discovered through coverage improvement 

efforts. Once selected, the survey returns to the same housing units every other year for data collection. Respondents 

for the survey consist of occupants of existing housing units as well as property owners of vacant housing units. 

SOC Background 

SOC Survey

The SOC is one of the most comprehensive new, privately-owned, residential housing survey in the U.S. The survey 

provides national and regional data on a range of topics. Topics covered by the survey include start and completion 

dates, house characteristics (such as the number of bedrooms, bathrooms, and square footage), and sales data (such 

as the sales date, pricing, and financing). Sales data provided only for new single-family houses. The SOC is 

partially funded by HUD and conducted by the U.S. Census Bureau. 

SOC Design

The SOC is a housing unit survey conducted on a continuous monthly basis. The SOC consists of new, privatelyowned, residential housing units sampled from predefined permit issuing and predefined non-permit issuing areas. 

SOC Sample

Housing units selected for the SOC represent a cross section of all new, privately-owned, residential housing units 

constructed in the U.S. Each month a sample of new, privately-owned, residential housing units are created through 

one of two methods. The first method includes sampling of building permits in predetermined areas requiring a 

building permit to authorize new housing unit construction. Surveying of these predetermined permit issuing areas 

takes place on a monthly basis. The second method includes physical canvassing of predetermined areas that do not 

require a building permit to authorize new housing unit construction. Surveying of these predetermined non-permit 

issuing areas takes place on a monthly or quarterly basis. Reselection of new predetermined permit and non-permit 

issuing areas takes place approximately every 20 years. 

Once a housing unit is selected, the survey returns to the same housing unit approximately every month from 

authorization of construction (or discovery via canvassing) through completion (or occupancy) and, if necessary, 

sale (for single-family houses). Respondents for the survey consist of builders, owners, and sales agents of new, 

privately-owned, residential housing units. 

The AHS and the SOC are sample surveys. Estimates based on sample surveys may differ from estimates obtained 

from a complete census. The accuracy of an estimate based on a sample survey is subject to the joint effects of both 

sampling errors and nonsampling errors. For the purposes of this paper, I will not discuss these errors. See the 

Reference section for additional information regarding these surveys. 

Methods 

Data Sources

This paper examines housing square footage estimates reported by the AHS and the SOC. The data sources used to 

obtain these estimates consist of the 2011 AHS National/Metropolitan Public Use File (or PUF, version 1.2) and 

2001-2013 SOC Internal Microdata Files. 
3 

AHS Data

The AHS PUF contains 186,448 observations. Analysis of housing square footage estimates occurred upon a subset 

of these observations. For the purposes of this paper, only detached, single housing unit buildings built from 2002-

2011 with between 100-13,000 square feet were included in the analysis. Additional variables relating to geography 

(U.S., Northeast, Midwest, South, and West Region geographic levels), the type of foundation (basement, crawl 

space, slab, etc.), number of floors (1, 2, 3+), square footage (both originally reported and additional changes, if 

available), and weights were also taken into consideration. Excluded from analysis are observations containing 

missing data or square footage data outside 100-13,000 square feet. The final subset contained 10,212 observations. 

SOC Data

Upon initial creation, the 2001-2013 SOC Internal Microdata File contained 674,024 observations. Analysis of 

housing square footage estimates occurred upon a subset of these observations. For the purposes of this paper, only 

detached, single housing unit buildings completed from 2002-2011 with between 100-13,000 square feet were 

initially included in the analysis. Additional variables relating to “geography” (U.S., Northeast, Midwest, South, and 

West Region geographic levels), the type of foundation (basement, crawl space, slab, etc.), type of basement 

(finished or unfinished), number of floors (Split Level, 1, 2, 3+), square footage, square footage dimensions (interior 

or exterior), and weights were also taken into consideration. Excluded from analysis are observations containing 

missing data or square footage data outside 100-13,000 square feet. The final subset contained 190,233 observations. 

Square Footage Estimates and Standard Errors

Weighted mean square footage estimates, and their associated standard errors, reported between the AHS and the 

SOC were calculated. Calculation of the estimates occurred at the U.S. and Regional geographic levels by year built. 

Corresponding estimates at lower geographic levels are not available. The SAS UNIVARIATE procedure produced 

the estimates and associated standard errors. See the Reference section for additional information regarding this 

procedure. 

Significance Testing

Commonly used parametric statistical testing procedures assume data are independent and normally distributed. As 

the AHS and SOC are independent surveys, attention shifted to the data distributions. Normally distributed data 

should appear as a straight diagonal line on a probability plot. Figure 1 and Figure 2 on the following page display 

weighted normal probability plots for both the AHS and the SOC mean square footage in detached single-family 

houses built from 2002-2011, respectively. Both sets of data depart from this standard, indicating the data are not 

normally distributed. Thus, parametric statistical testing procedures are inappropriate. 

This paper employed the Wilcoxon Rank Sum non-parametric statistical test to test for statistical significance 

(Pappas & DePuy, 2004). The assumptions for this test require the data be independent and identically distributed, 

and that the shapes and spreads of the distributions are the same. Both the AHS and the SOC meet these conditions. 

Results from the Wilcoxon Rank Sum test will report on statistically significant differences (if present) between the 

underlying housing square footage distributions of the AHS and the SOC at a 90% confidence level. 
4 

Figure 1: Weighted Normal Probability Plot of Mean Square Footage 

Reported by AHS in Detached Single-Family Houses Built 2002-2011 

12750+ * 

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 | 

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10250+ * 

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 7750+ * ++ 

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 250+* ++ 

 +----+----+----+----+----+----+----+----+----+----+ 

 -2 -1 0 +1 +2

Source: 2011 AHS National/Metropolitan Public Use File (v 1.2); Cases with 

missing data or square footage outside 100-13,000 removed from analysis 

Figure 2: Weighted Normal Probability Plot of Mean Square Footage 

Reported by SOC in Detached Single-Family Houses Built 2002-2011 

13250+ * 

 | * 

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 +----+----+----+----+----+----+----+----+----+----+ 

 -2 -1 0 +1 +2

Source: 2001-2013 SOC Internal Microdata Files; Cases with missing 

data or square footage outside 100-13,000 removed from analysis
5 

Housing Square Footage Estimates 

Table 1 shows the number of cases analyzed for the AHS, the mean square footage reported, and associated standard 

errors in detached single-family houses built from 2002-2011 at the U.S. and Regional geographic levels.

2002 1,283 69 307 484 423 2,942 3,952 3,076 2,811 2,760 2.2% 10.0% 4.5% 3.7% 3.7%

2003 1,336 80 294 546 416 2,849 3,045 2,905 2,876 2,676 2.1% 8.5% 4.6% 3.5% 2.7%

2004 1,386 79 311 543 453 2,736 3,480 3,021 2,676 2,398 1.9% 8.4% 4.4% 3.1% 2.7%

2005 1,693 91 318 727 557 2,854 3,031 3,186 2,697 2,826 1.9% 8.9% 4.5% 2.8% 3.0%

2006 1,510 81 279 710 440 2,900 3,356 3,130 2,799 2,827 1.9% 9.4% 4.8% 2.7% 3.5%

2007 1,171 54 208 572 337 2,970 4,087 3,531 2,679 3,009 2.4% 10.8% 5.8% 3.2% 4.5%

2008 793 64 129 367 233 2,995 2,783 2,885 3,050 3,043 2.8% 10.4% 7.6% 4.0% 4.7%

2009 465 38 97 204 126 2,958 3,882 2,785 3,044 2,591 3.8% 14.0% 8.6% 5.1% 8.2%

2010 424 30 96 199 99 2,502 2,752 2,055 2,624 2,523 3.8% 16.3% 4.8% 5.7% 8.0%

2011 151 6 39 68 38 3,281 3,106 3,985 3,190 2,802 6.0% 16.8% 12.8% 8.2% 12.5%

2002-11 10,212 592 2,078 4,420 3,122 2,887 3,356 3,071 2,790 2,755 0.8% 3.4% 1.8% 1.1% 1.3%

1

Source: 2011 AHS National/Metropolitan Public Use File (v 1.2); Cases with missing data or square footage outside 100-13,000 removed from analysis

NortheastMidwest South WestUnited 

States

NortheastMidwest South WestUnited 

States

Table1: Mean Square Footage Reported by AHS1 in Detached Single-Family Houses

Year 

Built

Cases Analyzed Square Footage Standard Errors

United 

States

NortheastMidwest South West

The overall mean square footage reported by the AHS over this time period ranges from 2,755 square feet in the 

West to 3,356 square feet in the Northeast. The associated standard errors are generally below 10% except for year 

2011 and in the Northeast. Note the decreasing sample size in the Northeast over this time corresponds to an 

increasing standard error. 

Similarly to Table 1, Table 2 shows the number of cases analyzed for the SOC, the mean square footage reported, 

and associated standard errors in detached single-family houses built from 2002-2011 at the U.S. and Regional 

geographic levels. 

2002 24,029 2,931 4,792 10,575 5,731 2,392 2,676 2,330 2,370 2,389 0.3% 0.7% 0.6% 0.4% 0.5%

2003 23,584 2,658 4,616 10,416 5,894 2,406 2,617 2,338 2,402 2,406 0.2% 0.8% 0.6% 0.4% 0.5%

2004 24,383 2,785 5,020 10,624 5,954 2,422 2,684 2,352 2,414 2,418 0.2% 0.7% 0.6% 0.4% 0.5%

2005 23,714 2,541 4,797 10,677 5,699 2,519 2,718 2,438 2,534 2,498 0.3% 0.8% 0.7% 0.4% 0.6%

2006 22,854 2,036 4,229 10,932 5,657 2,569 2,850 2,419 2,578 2,576 0.3% 1.0% 0.7% 0.4% 0.5%

2007 20,144 1,652 3,411 10,087 4,994 2,627 2,777 2,451 2,655 2,629 0.3% 1.2% 0.8% 0.5% 0.6%

2008 15,816 1,255 2,763 8,084 3,714 2,635 2,847 2,404 2,673 2,649 0.4% 1.4% 1.0% 0.5% 0.8%

2009 11,556 1,014 2,009 5,939 2,594 2,548 2,761 2,355 2,565 2,569 0.5% 1.6% 1.1% 0.6% 0.9%

2010 12,621 1,070 2,362 6,515 2,674 2,451 2,778 2,327 2,438 2,452 0.4% 1.6% 1.0% 0.5% 0.9%

2011 11,532 980 2,096 5,923 2,533 2,566 2,728 2,409 2,612 2,505 0.4% 1.6% 1.0% 0.6% 0.8%

2002-11 190,233 18,922 36,095 89,772 45,444 2,506 2,736 2,384 2,519 2,500 0.1% 0.3% 0.3% 0.2% 0.2%

1

Source: 2001-2013 SOC Internal Microdata Files; Cases with missing data or square footage outside 100-13,000 removed from analysis

South West

Midwest South WestUnited 

States

NortheastMidwestNortheastMidwest South WestUnited 

States

Northeast

Table 2: Mean Square Footage Reported by SOC1 in Detached Single-Family Houses

Year 

Built

Cases Analyzed Square Footage Standard Errors

United 

States

For the SOC, the overall mean square footage reported over this time period ranges from 2,500 square feet in the 

West to 2,736 square feet in the Northeast. The associated standard errors are consistently below 2%. These reported 

square footages and associated standard errors are lower than those reported by the AHS. Note that the SOC sample 

sizes are higher than those from the AHS. Additional discussion regarding sample sizes will take place later. 
6 

Turning our attention to the comparison between these two surveys, Table 3 shows the percent differences 

(calculated by the difference between the AHS and the SOC estimates with respect to the SOC estimate) and the 

associated statistical significances in detached single-family houses built from 2002-2011 at the U.S. and Regional 

geographic levels. 

2002 23% 48% 32% 19% 16% 0.0001 * 0.5890 0.0001 * 0.6688 0.0724 *

2003 18% 16% 24% 20% 11% 0.0208 * 0.9566 0.0001 * 0.9028 0.0656 *

2004 13% 30% 28% 11% -1% 0.0001 * 0.1954 0.0001 * 0.0074 * 0.0881 *

2005 13% 12% 31% 6% 13% 0.0840 * 0.1886 0.0001 * 0.5475 0.4971

2006 13% 18% 29% 9% 10% 0.6327 0.3874 0.0001 * 0.0989 * 0.7870

2007 13% 47% 44% 1% 14% 0.3750 0.2690 0.0001 * 0.0010 * 0.2474

2008 14% -2% 20% 14% 15% 0.8933 0.0553 * 0.0068 * 0.0493 * 0.2580

2009 16% 41% 18% 19% 1% 0.4338 0.9168 0.0039 * 0.7406 0.1631

2010 2% -1% -12% 8% 3% 0.8308 0.3519 0.2298 0.8253 0.5046

2011 28% 14% 65% 22% 12% 0.0981 * 0.8337 0.0145 * 0.8734 0.3485

2002-11 15% 23% 29% 11% 10% 0.0001 * 0.6033 0.0001 * 0.2407 0.0389 *

1

Source: 2011 AHS National/Metropolitan Public Use File (v 1.2); Cases with missing data or square footage outside 100-13,000 removed from analysis

2

Source: 2001-2013 SOC Internal Microdata Files; Cases with missing data or square footage outside 100-13,000 removed from analysis

* Statistically significant differences in the underlying square footage distributions of the AHS and the SOC at a 90% confidence level

 NortheastMidwest South WestYear 

Built

Table 3: Percent Difference in Mean Square Footage Reported by AHS1 and SOC2 in Detached Single-Family Houses

United 

States

NortheastMidwest South WestUnited 

States

Percent Difference (AHS-SOC / SOC) Statistical Significance Probabilities

The majority of percent differences between the AHS and the SOC are positive. This indicates the AHS mean square 

footage is larger than the corresponding SOC square footage. Also, note how the statistical significance probabilities 

are more significant for earlier years versus recent years. These results indicate there are statistically significant 

differences in the underlying housing square footage distributions between the two surveys. 

This poses an interesting question. Why are there more statistically significant differences between the surveys in 

earlier years as opposed to recent years? Can you compare estimates obtained from the surveys? Well the answer is 

yes! However to accomplish this one must take into account issues associated with housing square footage 

estimates. 

Housing Square Footage Issues 

This paper will discuss four issues associated with housing square footage estimates. These issues include 

differences between the AHS and the SOC regarding sample sizes, survey designs, and square footage definitions. 

An additional issue also includes conversion issues specifically related to the SOC. Together these issues suggest 

reasons for housing square footage estimate differences reported between the surveys. 

Sample Size Issues

Table 4 on the following page shows sample sizes used from the AHS and the SOC to analyze mean square footage 

reported in detached single-family houses built from 2002-2011 at the U.S. and Regional geographic levels. 

Overall, the AHS contains far less observations than the SOC (10,212 AHS observations to 190,233 SOC 

observations). Within the AHS, sample sizes for the Northeast geographical area (592 observations) and for 2011 as 

a whole (151 observations) are particularly small. It takes a while to update the AHS sample with new residential 

construction. This lag in updating the AHS sample with new residential construction limits available comparisons 

over recent years to the SOC (which is entirely comprised of new residential construction). 

To address sample size issues, updated square footage analysis will be limited to detached single-family houses built 

from 2002-2010. Excluded from analysis are data from 2011. 
7 

2002 1,283 69 307 484 423 24,029 2,931 4,792 10,575 5,731

2003 1,336 80 294 546 416 23,584 2,658 4,616 10,416 5,894

2004 1,386 79 311 543 453 24,383 2,785 5,020 10,624 5,954

2005 1,693 91 318 727 557 23,714 2,541 4,797 10,677 5,699

2006 1,510 81 279 710 440 22,854 2,036 4,229 10,932 5,657

2007 1,171 54 208 572 337 20,144 1,652 3,411 10,087 4,994

2008 793 64 129 367 233 15,816 1,255 2,763 8,084 3,714

2009 465 38 97 204 126 11,556 1,014 2,009 5,939 2,594

2010 424 30 96 199 99 12,621 1,070 2,362 6,515 2,674

2011 151 6 39 68 38 11,532 980 2,096 5,923 2,533

2002-11 10,212 592 2,078 4,420 3,122 190,233 18,922 36,095 89,772 45,444

1

Source: 2011 AHS National/Metropolitan Public Use File (v 1.2); Cases with missing data or square

 footage outside 100-13,000 removed from analysis

2

Source: 2001-2013 SOC Internal Microdata Files; Cases with missing data or square footage outside

 100-13,000 removed from analysis

NortheastMidwest South West

Table 4: Cases Analyzed for Mean Square Footage Reported in Detached Single-Family Houses

Year 

Built

Cases Analyzed for AHS1 Cases Analyzed for SOC2

United 

States

NortheastMidwest South WestUnited 

States

Survey Design Issues 

Figure 3 charts the mean square footage percent difference (calculated by the difference between the AHS and the 

SOC estimate with respect to the SOC estimate) in detached single-family houses built from 2002-2011 at the U.S. 

and Regional geographic levels. 

1

Source: 2011 AHS National/Metropolitan Public Use File (v 1.2); Cases with missing data or square footage outside 100-13,000 removed from analysis 

2

Source: 2001-2013 SOC Internal Microdata Files; Cases with missing data or square footage outside 100-13,000 removed from analysis 
8 

The pattern of alignment for years 2002-2006 (earlier years) is similar, with almost all percentages showing positive 

differences. Percent differences for year 2002 are also higher than for years 2003-2006. Positive differences indicate 

the square footage reported by the AHS is higher than the corresponding SOC square footage. This makes sense 

given the AHS is a longitudinal survey. The AHS interviews occupants of existing housing units every other year, 

and square footages may in fact change over time (for example, if an addition to a house is completed). 

Patterns for years 2007-2011 (recent years) are more varied. Remember the SOC is a monthly survey. The SOC 

interviews builders, owners, and/or sales agents of new, privately-owned, residential housing units from 

authorization through completion (or occupancy). For the SOC, square footage is a snapshot taken at the time a 

house is completed. So in recent years, single-family detached houses are relatively newer, thus the square footage 

may be more likely to match up to the square footage available immediately after house construction. This 

difference in survey design limits available comparisons over earlier years between the surveys as the available 

square footage in existing housing units change, due to construction of additions, for example. 

To address survey design issues, updated square footage analysis will be limited to detached single-family houses 

built from 2007-2010. In addition, updated square footage analysis will obtain original AHS square footage 

estimates where applicable. 

Square Footage Definition Issues

The housing square footage definitions used by the AHS and the SOC are different. The AHS and the SOC handle 

basements, and their associated square footages, differently. Specifically: 

 

AHS housing square footage: “...excluded from the calculation of square footage are unfinished attics, carports, 

attached garages, porches that are not protected from weather (such as screened 

porches), and mobile home hitches. Both finished and unfinished basements are 

included. Square footage is based on respondent’s estimate of the size of the unit.”

SOC housing square footage: “Square footage of floor area, defined as all completed finished floor space, 

including space in basements and attics with finished walls, floors, and ceilings. This 

does not include a garage, carport, porch, unfinished attic or utility room. 

Unfinished areas of the basement are excluded.” 

There are also differences in how the surveys capture basement information. The AHS only captures presence of a 

basement as part of the physical house structure. Whether or not the basement is finished does not influence

collection of the square footage, as both finished and unfinished areas of the basement should be included in the 

square footage. The SOC too captures presence of a basement as part of the physical house structure. Where a 

basement is identified, the SOC proceeds to capture whether the basement is finished (all or part) or unfinished. 

Only finished areas of a basement should be included in the square footage. 

In essence, the AHS is capturing living space (where all areas of the basement are included) while the SOC is 

capturing floor space (where only finished areas of the basement are included). Based on these definitional 

differences, comparisons between the surveys must take into account both the presence and type of basement. 

To address square footage definitional issues, updated square footage analysis will assume unfinished housing 

square footage is primarily located in the basement. Analysis will break out structures based upon presence and 

type of basement. 

External Conversion Issues

As noted above, the AHS collects and estimates housing square footage “...based on respondent’s estimate of the 

size of the unit.” This respondent varies by survey. Remember the AHS respondent consists of mainly occupants or 

property owners. Occupants in particular may be estimating the size of the unit based upon memory, thus increasing 
9 

difficulty in obtaining accurate estimates. The SOC respondent, on the other hand, consists of the builder, owner, or 

sales agent. These respondents may have access to more accurate information in the way of construction blue prints 

or floor plans, thus decreasing difficulty in obtaining accurate estimates. 

In addition, the SOC also collects the dimension (interior, exterior, or unknown) upon which the square footage is

based. For estimating, the SOC converts all reported square footages to exterior dimensions through the following 

procedures: 

Square footages based on exterior dimensions not increased. 

Square footages based on interior dimensions increased 8%. 

Square footages based on unknown dimensions increased 4%. 

For example, if the AHS respondent reports the square footage as 2,000 square feet, the AHS estimate is 2,000 

square feet. If the SOC respondent reports the square footage as 2,000 square feet based on interior dimensions, the 

SOC estimate is 2,160 square feet. 

For more information, Table 5 shows the number of cases analyzed for the SOC, the number of these cases reporting 

square footages based on exterior dimensions, and the resulting percentage of cases being converted to exterior 

dimensions for detached single-family houses built from 2002-2011 at the U.S. and Regional geographic levels. 

At the U.S. geographic level, the percentage of cases converting to exterior dimensions has climbed steadily from 

62% in 2002 to 72% in 2011. This conversion process in effect serves to increase the housing square footage

estimates reported by the SOC, thus potentially altering comparisons between the surveys. 

2002 24,029 2,931 4,792 10,575 5,731 9,011 1,074 2,152 3,973 1,812 62% 63% 55% 62% 68%

2003 23,584 2,658 4,616 10,416 5,894 8,510 1,025 2,063 3,610 1,812 64% 61% 55% 65% 69%

2004 24,383 2,785 5,020 10,624 5,954 9,146 1,167 2,282 3,959 1,738 62% 58% 55% 63% 71%

2005 23,714 2,541 4,797 10,677 5,699 8,232 1,039 2,055 3,642 1,496 65% 59% 57% 66% 74%

2006 22,854 2,036 4,229 10,932 5,657 6,775 689 1,405 3,467 1,214 70% 66% 67% 68% 79%

2007 20,144 1,652 3,411 10,087 4,994 5,345 512 966 2,857 1,010 73% 69% 72% 72% 80%

2008 15,816 1,255 2,763 8,084 3,714 4,323 425 765 2,246 887 73% 66% 72% 72% 76%

2009 11,556 1,014 2,009 5,939 2,594 3,002 283 527 1,642 550 74% 72% 74% 72% 79%

2010 12,621 1,070 2,362 6,519 2,674 3,421 311 584 1,847 679 73% 71% 75% 72% 75%

2011 11,532 980 2,096 5,923 2,533 3,194 296 565 1,634 699 72% 70% 73% 72% 72%

2002-11 190,233 18,922 36,095 89,776 45,444 60,959 6,821 13,364 28,877 11,897 68% 64% 63% 68% 74%

1

Source: 2001-2013 SOC Internal Microdata Files; Cases with missing data or square footage outside 100-13,000 removed from analysis

Table 5: Cases Analyzed for Mean Square Footage Reported in Detached Single-Family Houses

Year

Cases Analyzed for SOC1 Cases Reporting Exterior Dimensions Percent Cases Converting Dimensions

United 

States

NortheastMidwest South WestNortheastMidwest South WestUnited 

States

NortheastMidwest South WestUnited 

States

To address external conversion issues, updated square footage analysis will assume the SOC housing square

footage estimate is collected directly from the respondent (similarly to the AHS) with no conversion to exterior 

dimensions applied. 

Updated Square Footage Analysis 

Now I will rerun the original square footage analysis taking into account the assumptions noted above when 

addressing issues associated with housing square footage. To recap, the updated analysis will: 

Remove recent year (2011) comparisons given lag in updating AHS sample with new residential construction. 

Remove earlier year (2002-2006) comparisons given available square footage changes over time (i.e. additions). 

Break out basement presence and type given differences in how surveys define square footage. 

Remove exterior square footage conversion applied to the SOC square footage estimates. 
10

Table 6 shows the updated number of cases analyzed for the AHS, the mean square footage reported, and associated 

standard errors in detached single-family houses by basement presence built from 2007-2010 at the U.S. and 

Regional geographic levels. 

First, note there are not as many detached single-family houses with basements as there are houses without

basements in the AHS (827 observations with a basement to 2,026 observations without a basement). There are also 

a limited number of houses without basements in the Northeast (20 observations). Remember smaller sample sizes 

correspond to larger standard errors. 

With Basement

2007 307 48 156 61 42 3,958 4,387 3,513 3,883 5,050 4% 11% 6% 10% 12%

2008 239 57 102 44 36 3,614 3,061 3,186 4,378 4,540 5% 10% 8% 10% 11%

2009 148 35 73 28 12 3,709 3,653 3,261 4,226 3,890 6% 14% 9% 11% 24%

2010 133 26 76 19 12 3,036 3,081 2,229 4,596 3,555 7% 17% 5% 19% 25%

2007-10 827 166 407 152 102 3,686 3,599 3,170 4,175 4,514 3% 6% 4% 6% 8%

No Basement

2007 864 6 52 511 295 2,623 2,422 3,567 2,481 2,709 3% 14% 14% 3% 4%

2008 554 7 27 323 197 2,681 1,371 1,738 2,752 2,798 3% 22% 9% 4% 5%

2009 317 3 24 176 114 2,590 6,075 1,613 2,733 2,429 5% 54% 13% 6% 9%

2010 291 4 20 180 87 2,279 1,393 1,472 2,375 2,265 4% 7% 6% 5% 7%

2007-10 2,026 20 123 1,190 693 2,590 2,265 2,658 2,568 2,640 2% 23% 10% 2% 3%

1

Source: 2011 AHS National/Metropolitan Public Use File (v 1.2); Cases with missing data or square footage outside 100-13,000 removed from analysis

 First interview square footage determined where applicable.

Table 6: Mean Square Footage Reported by AHS1 in Detached Single-Family Houses by Basement

Year

Cases Analyzed Square Footage Standard Errors

United 

States

United 

States

NortheastMidwestNortheastMidwest South WestUnited 

States

Northeast South WestMidwest South West

Of more interest are the mean square footages themselves. The change in square footage ranges between detached 

single-family houses with and without a basement is evident. The mean square footages in houses with a basement 

reported by the AHS over this time are almost entirely over 3,000 square feet. The square footage ranges for houses 

without a basement are usually smaller. This result clearly shows additional square footage is available in houses 

with a basement. This may or may not indicate a corresponding increase in house quality. 

Table 7 on the following page shows the updated number of cases analyzed for the SOC, the mean square footage 

reported, and associated standard errors in detached single-family houses by basement presence and type built from 

2007-2010 at the U.S. and Regional geographic levels. 
11

Finished Basement

2007 1,423 180 587 320 336 3,633 3,641 3,357 3,856 3,836 1% 3% 2% 3% 2%

2008 1,252 121 504 311 316 3,699 3,727 3,253 4,171 3,930 1% 5% 2% 2% 3%

2009 849 105 333 205 206 3,642 3,615 3,235 4,265 3,717 2% 5% 2% 3% 3%

2010 880 85 420 201 174 3,404 3,429 3,281 3,588 3,443 2% 6% 2% 3% 3%

2007-10 4,404 491 1,844 1,037 1,032 3,616 3,626 3,293 3,976 3,781 1% 2% 1% 1% 1%

Unfinished Basement

2007 4,888 1,172 2,184 839 693 2,410 2,527 2,213 2,855 2,232 1% 1% 1% 2% 1%

2008 3,789 888 1,771 617 513 2,397 2,590 2,148 2,902 2,326 1% 2% 1% 2% 2%

2009 2,732 705 1,245 416 366 2,342 2,535 2,137 2,700 2,193 1% 2% 1% 2% 2%

2010 3,139 808 1,455 470 406 2,303 2,543 2,104 2,478 2,248 1% 1% 1% 2% 2%

2007-10 14,548 3,573 6,655 2,342 1,978 2,378 2,547 2,164 2,789 2,253 0% 1% 1% 1% 1%

No Basement

2007 13,833 300 640 8,928 3,965 2,411 2,420 1,815 2,448 2,406 0% 3% 1% 0% 1%

2008 10,775 246 488 7,156 2,885 2,403 2,568 1,828 2,446 2,369 0% 3% 2% 1% 1%

2009 7,975 204 431 5,318 2,022 2,305 2,385 1,736 2,347 2,309 1% 4% 2% 1% 1%

2010 8,602 177 487 5,844 2,094 2,217 2,548 1,643 2,262 2,191 0% 5% 2% 1% 1%

2007-10 41,185 927 2,046 27,246 10,966 2,361 2,475 1,770 2,401 2,352 0% 2% 1% 0% 0%

1

Source: 2001-2013 SOC Internal Microdata Files; Cases with missing data or square footage outside 100-13,000 removed from analysis

 No external square footage conversion factor applied.

Midwest South West South WestUnited 

States

Table 7: Mean Square Footage Reported by SOC1 in Detached Single-Family Houses by Basement

Year

Cases Analyzed Square Footage Standard Errors

United 

States

NortheastNortheastMidwest South WestUnited 

States

NortheastMidwest

First, as discussed earlier, the SOC breaks down detached single-family houses not just by basement presence, but 

also by basement type. That is, whether the basement is finished (partially or fully) or entirely unfinished. It is 

interesting to note almost 70% of the SOC observations over this time do not contain a basement (41,185 

observations with no basement from a total of 60,137 observations). Also notable, where there is a basement, it is 

more likely to be an unfinished basement (4,404 observations with a finished basement versus 14,548 observations 

with an unfinished basement). Remember for the SOC only finished areas of a basement should be included in the 

square footage, unlike for the AHS where all basement areas are included in the square footage. 

Again, of more interest are the mean square footages themselves. Based upon the AHS findings discussed earlier, 

one would expect square footage ranges for detached single-family houses with a finished basement to be higher 

than for houses without a basement. This is true given that the mean square footages in houses with a finished 

basement reported by the SOC over this time are entirely over 3,200 square feet. The square footage ranges for 

houses without a basement are smaller, all less than 2,600 square feet. This result clearly indicates additional square 

footage is available in houses with a basement. 

Of equal (or maybe more) interest, are the mean square footages for detached single-family houses with unfinished 

basements. Here, the SOC does not capture any area of the basement in the square footage, so in theory one would 

expect square footage ranges for houses with unfinished basements to be lower than for houses with a finished 

basement. This is true. However, the results also show a slight difference between houses with an unfinished 

basement when compared to houses with no basement (2,164 – 2,789 square feet in houses with an unfinished 

basement over 2007-2010 versus 1,770 – 2,475 square feet in houses with no basement over the same time). This 

may indicate more of a fundamental difference between the quality of houses with and without basements. At any 

rate, houses with an unfinished basement as reported in the SOC do not match up well with the AHS (where only the 

presence of a basement is captured). As a result, further comparison between the surveys will remove this particular 

SOC breakout. 

Finally, let us now turn our attention to the updated comparison between the surveys. Table 8 on the following page 

shows the percent differences (calculated by the difference between the AHS and the SOC estimates with respect to 

the SOC estimate) and the associated statistical significance in detached single-family houses by basement presence 

built from 2007-2010 at the U.S. and Regional geographic levels. 
12

Table 8: Percent Difference in Mean Square Footage Reported by AHS1 and SOC2 in Detached Single-Family Houses by Basement

2007 9% 20% 5% 1% 32% 0.0001 * 0.0362 * 0.0848 * 0.0351 * 0.2067

2008 -2% -18% -2% 5% 16% 0.0001 * 0.0001 * 0.0483 * 0.0280 * 0.2148

2009 2% 1% 1% -1% 5% 0.0001 * 0.0474 * 0.4163 0.0026 * 0.1450

2010 -11% -10% -32% 28% 3% 0.0001 * 0.0775 * 0.0001 * 0.0795 * 0.3389

2007-10 2% -1% -4% 5% 19% 0.0001 * 0.0001 * 0.0001 * 0.0001 * 0.0233 *

2007 9% 0% 97% 1% 13% 0.9057 0.8686 0.0909 * 0.5422 0.5638

2008 12% -47% -5% 13% 18% 0.2209 0.0235 * 0.7675 0.9783 0.0135 *

2009 12% 155% -7% 16% 5% 0.2798 0.5766 0.7443 0.0895 * 0.9364

2010 3% -45% -10% 5% 3% 0.0766 * 0.0142 * 0.1913 0.0867 * 0.1133

2007-10 10% -8% 50% 7% 12% 0.0094 * 0.0126 * 0.0408 * 0.1381 0.0059 *

1

Source: 2011 AHS National/Metropolitan Public Use File (v 1.2); Cases with missing data or square footage outside 100-13,000 removed from analysis

 First interview square footage determined where applicable.

2

Source: 2001-2013 SOC Internal Microdata Files; Cases with missing data or square footage outside 100-13,000 removed from analysis

 No external square footage conversion factor applied.

* Statistically significant differences in the underlying square footage distributions of the AHS and the SOC at a 90% confidence level

Midwest South WestUnited 

States

 NortheastMidwest South West

AHS Basement / SOC Finished Basement

AHS No Basement / SOC No Basement

Year 

Built

Percent Difference (AHS - SOC / SOC) Statistical Significance Probabilities

United 

States

Northeast

Note how the percent differences between the surveys for detached single-family houses with basements are now 

different than those obtained from the initial analysis. Quite a few differences are now smaller (less than 6% in 

magnitude). This indicates estimates reported from the AHS and the SOC are now more similar. The differences are 

also no longer exclusively positive, indicating the SOC mean square footage may be larger than the corresponding 

AHS square footage. This result is interesting as it is unlikely a new housing unit will lose square footage so quickly 

after construction. In fact, this result may hit more specifically on the difficulty respondents from both surveys have 

in estimating square footage. 

Also, note the statistical significance probabilities. In the initial analysis, most statistical significance took place in 

earlier years. In the updated analysis, significant differences are noted in recent years, but occurring more often 

amongst detached single-family houses with basements. These results indicate there are statistically significant 

differences in the underlying housing square footage distributions between the two surveys for houses with 

basements. This makes sense given the SOC square footage estimates for houses with a basement may in fact be less 

than the corresponding AHS estimate. Remember the SOC does not capture unfinished areas of the basement (which 

may be more likely to remain unfinished due to the presence of a washer, dryer, and/or water heater). These areas 

should be included in the AHS estimate, thus making the AHS square footage larger than the corresponding SOC 

square footage. 

Proposed Enhancements 

In summary, interpretation of housing square footage estimates reported by the AHS and the SOC is not a 

straightforward process. To interpret these results correctly, addressing issues associated with housing square 

footage estimates is necessary. These issues are not all encompassing, nor are they constrained to any one particular 

survey area. From when data are collected – to what types of data are collected – to what, if any, post-processing 

procedures are applied – the occurrence and impact of issues must be taken into consideration. 

This paper, in addition to identifying and addressing housing square footage issues, proposes two enhancements to 

the AHS and the SOC. If enacted, these enhancements should assist with future comparisons between the surveys. 

The first enhancement regards data collection for the AHS. The second enhancement regards additional research for 

the SOC. 
13

Proposed AHS Enhancement – Capture of additional information regarding basement type would assist with 

comparisons between the AHS and the SOC. Specifically indicating whether a basement is finished (fully or 

partially) or unfinished, as currently collected in the SOC, would be useful. 

Proposed SOC Enhancement – Aside from differences in house structure, conversion to exterior dimensions applied 

to reporting of housing square footage for the SOC needs further research. For the purposes of this paper, all 

assumptions addressing housing square footage issues were applied collectively. The individual effect of “marking 

up” housing square footage estimates reported by the SOC was not addressed individually. Additional research here 

is necessary. 

Acknowledgement 

I would like to recognize the following persons who helped make this paper possible. First, I would like to recognize 

Erica Filipek and members of the Residential Construction Branch for their review and comments. I would also like 

to recognize Bonnie Kegan for her guidance regarding statistical testing procedures. Thank you! 

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