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  Institute of Housing Technologies
Improving the Real Estate Information Network
How Do You Measure A House?

The total floor area of a house is one of the most important pieces of information about a property that the parties in a real property transaction need to know. Accurate measurements are needed for home buyers, other agents, and appraisers to get accurate and consistent information to use in comparing houses. Buyers rely on square footage information provided to them by their real estate agent when they are purchasing a home. Sellers require an accurate square footage determination to be certain that they are getting the best price for the home they are selling and to be protected from the possibility of lawsuits filed when purchasers discovered that a home was significantly smaller than was stated by the seller or the seller's real estate agent. Agents listing a property for sale are responsible for reporting accurately how much heated living area a home contains.

The North Carolina Real Estate Commission says, “Although real estate agents are not required by the Real Estate License Law or Real Estate Commission rules to report the square footage of properties offered for sale (or rent), when they do report square footage, it is essential that the information they give prospective purchasers be accurate.” All agents licensed by NCREC are expected to be able to accurately calculate the square footage of most dwellings. The Carolina Multiple Listing Service (CMLS) requires listing agents to report the Gross Heated Living Area of a residence as determined by a measurement of the dwelling. It is very important to know as an agent, when you are comparing homes when performing a CMA, how the square footage was calculated.

When reporting square footage, real estate agents should carefully follow the guidelines as approved by the American National Standards Institute, Inc. (ANSI) which are recognized by the North Carolina Real Estate Commission. Agents should be able to identify which standard is used in North Carolina.

The ANSI® Standard

In 1996, the American National Standards Institute (ANSI) adopted a standard for measuring single-family residential buildings, called the American National Standard Z765-1996. This standard was last revised in 2003. The standards were developed by consulting with several industry groups, including Realtors, builders, architects, and appraisers. The ANSI standards are NOT LAW, only a voluntary guide. The ANSI Standard is the accepted method by National Association of Realtors and by the North Carolina Real Estate Commission. The ANSI standard bases floor area calculations on the exterior dimensions of the building at each floor level, and include all interior walls and voids. "Finished area" is defined as “an enclosed area in a house suitable for year-round use, embodying walls, floors, and ceilings that are similar to the rest of the house.” 

A 16-page booklet describing the ANSI standards with examples and illustrations can be purchased for $20.00 (plus $4.00 shipping and handling) from the National Association of Home Builders (NAHB)Research Center in Maryland at 301-249-4000.

The North Carolina Real Estate Commission gives this guideline for “Heated Living Area:”

“Living area (sometimes referred to as "heated living area" or "heated square footage") is space that is intended for human occupancy and is:

1. Heated by a conventional heating system or systems (forced air, radiant, solar, etc.) that are permanently installed in the dwelling - not a portable heater - which generates heat sufficient to make the space suitable for year-round occupancy; 

2. Finished, with walls, floors and ceilings of materials generally accepted for interior construction (e.g., painted drywall/sheet rock or paneled walls, carpeted or hardwood flooring, etc.) and with a ceiling height of at least seven feet, except under beams, ducts, etc. where the height must be at least six feet four inches [Note: In rooms with sloped ceilings (e.g., finished attics, bonus rooms, etc.) you may also include as living area the portion of the room with a ceiling height of at least five feet if at least one-half of the finished area of the room has a ceiling height of at least seven feet.]; and 

3. Directly accessible from other living area (through a door or by a heated hallway or stairway).”

Measuring the House

Always start by measuring the outside of the first floor of the house. Begin measuring from any corner and work your way around the house. Move counter-clockwise around the house. It is best to do this the same way every time that you do it to avoid easily made errors and to make it easier to retrace your steps to track down any errors. Measure the exterior of the house to the nearest inch. If you use an “engineer’s scale” fiberglass tape (which is recommended), measure the exterior and interior walls to the nearest 0.05 foot, for example 23.25 feet. This will make your calculations considerably easier later.

If you can't get close to a wall because of landscaping or other obstacles, use your screwdriver to anchor the 100-foot tape on the ground away from the wall.

Draw your sketch and the write down the corresponding dimensions on the graph paper as you go, with each square representing one foot. For example, if the exterior dimension is 3.45’, you will draw a line that is 3 squares long. If the dimension is, 3.50’, draw your line 4 squares long. (Always round up to the next full number if the dimension is 0.50’ or greater.) As you move around the house making your sketch, place the exterior doors and chimneys in their approximate locations on your sketch. It is also helpful to make notes on your sketch of which walls have full height second floor walls that are the same as the walls on the first floor. It also may help you to include in your sketch where the porches, stoops, screen porches, patios, and other outdoor areas are located on your drawing as you go.

When you have completed your first floor exterior drawing, use your calculator to “square” your drawing. To square your sketch, add up all of the dimensions of parallel walls on each side. Opposite sides will be equal. If they are not, check for errors by re-measuring any of the walls to find your error.

When you are finished measuring the outside of the house, go inside and decide what to include and what not to include on each level. If the house has a garage, it is not to be included in the heated living area calculations. You must measure the garage out so that you can calculate this area separately.

You will draw a separate floor plan sketch for each level in the house. If there is a second or upper level, measure that area from the inside. To do this, go to the second floor and, when possible, begin on a corner on which you have a corresponding first floor corner. Begin your sketch from this point. Remember, you are measuring the EXTERIOR dimensions of the second floor so you will adding to the interior measurements the wall thicknesses to get the exterior dimensions. (0.40’ to account for the thickness of an exterior frame wall, 0.40’ for interior walls with finished drywall, and 0.70’ to account for exterior masonry veneered walls). Read NC Guideline **

When there are openings to the floor below, such as in an open foyer, subtract the opening from that level.

When there are stairs, include them on every level they serve, that is, count the floor area of the staircase on BOTH the first and second floor areas. Be sure to include the stairs in the second floor area when measuring out an open foyer.

As you gain experience measuring houses, you will find a number of difficulties that will present themselves with different house designs. Some two story houses and one and a half story homes have very few second floors exterior walls that will line up with the first floor exterior walls. It is very important before you begin measuring the upper floors of any house, to identify which of the interior walls are also the exterior walls of that level. I find it helpful to walk around and try to identify these walls before I begin the measurement.

For split-level designs, measure each level. It is helpful to measure the lower and main levels from the exterior together and then separate the levels by getting the interior measurements on each level once you have gone inside. You will measure the upper level separately from the interior of the house.

When measuring a basement, separate the finished basement area from the unfinished areas. Even if the basement is a “daylight” finished basement, the area is NEVER included with the above grade heated living area. The areas have to be reported separately from the above grade areas. Exclude any areas, such as porches & converted garages that are not finished or heated the same as the rest of the house (see the guidelines of “Heated Living Area” from the NCREC). 

Calculating the Square Footage

From your sketch of the dwelling, identify and separate living area from "other area." Calculate the living area (and other area) by multiplying the length times the width of each rectangular space. Then add your subtotals and round off your figure for total square footage to the nearest square foot.

When necessary, calculate the square footage of the first floor by dividing the area up into smaller rectangles and calculating the area of each of the rectangles. Add up the areas of the smaller rectangles to get the total square footage of each level.

Now, divide the second floor up into smaller rectangles and calculate the total square footage. Add these numbers together and this will be the total Gross Heated Living Area of the house you have measured.

Areas NOT included in the Heated Living Area Calculations

Basements and Below-Grade Floor Areas - Even if the below-grade areas are fully finished, they are not part of the finished floor area according to ANSI standards. Separate the areas from the heated living area and report them as “finished basement” and “unfinished basement”.

Attics, Lofts and Low Ceilings - Level ceilings must be at least 7 feet high, and at least 6 feet 4 inches under beams, ducts and other obstructions. If a room with a sloped ceiling meets the one-half-of-floor-area-over-7-feet requirement, then include all the floor space with a ceiling height over 5 feet. If it does not meet these requirements, then report the area as “finished attic” or “partially finished attic”. Lofts and finished attics must be accessible by a conventional stairway or other access to be counted. If you can only reach the loft by climbing a ladder, it's not part of the finished floor area regardless of the ceiling height.

Detached Rooms, Guest Cottages, Mother-in-Law Units & Dwelling Units - According to the ANSI standards, finished areas which are not connected to the main residence by a finished hall or stairway must be listed separately. If you have to leave the house to get to the room, it's not part of the finished floor area.

Measuring Townhouses and Condominiums

So far we have learned that when measuring a detached single family residence, the heated living area is determined by measuring the exterior dimensions of the building at each floor level, and include all interior walls and voids. But measuring attached townhouses and condominium units is not quite the same. Since these types of ownership are very different, it is extremely important to know the differences between townhouse units and condominium units. There are few guidelines to use to help you determine whether a unit is a condominium or a townhouse.

Townhouses are typically a group of two-story or three-story units that are horizontally attached to each other, sharing a “common wall”. Townhouse owners always own the land on which the townhouse is built; many times, when land is included, it can be verified through the tax or deed records. If the property you are measuring is truly a townhouse, it will have no units on top of it or below it. If it does, it is probably a condominium, and must be measured differently from a townhouse. However, it is not unusual for a condominium project to look like a townhouse project, that is, to have no other units above or below. So you should make sure by checking tax records or deed records to verify that the project is townhouses (with land included) and not condominium units.

As an attached dwelling, it is not possible to measure all of the exterior walls of a townhouse. It is necessary to measure a townhouse from the inside, and to do this, it is the same as measuring the second floor of a detached single family house. Begin at an interior corner that has an exterior wall. Add in the thickness of the exterior walls as you measure each “exterior” wall, 0.70’ for masonry veneer (brick or stone) and 0.40” for exterior frame walls. Remember to add 0.40’ for any interior walls that you measure. You will also add in 0.50’ for the “common wall” of a townhouse, that is, the wall that two units will share. An end unit townhouse will only have one common wall, but an interior unit will have two common walls.


A condominium unit is defined as “The absolute ownership of a unit in a multiunit building based on a legal description of the airspace the unit actually occupies, plus an undivided interest in the ownership of the common elements, which are jointly owned with the other condominium unit owners.” As the owner of a condominium unit only owns the airspace that the unit occupies you do not include any of the exterior walls in your measurement.

Proposed Construction

When you are reporting the heated living area of a house that is not yet built or is under construction, you will have to base your calculations on dimensions in blue prints. Using these dimensions, draw the sketch out on graph paper as if you were measuring the house, and then calculate the square footage of the dwelling. You must report that the square footage you are reporting is based on plan dimensions and that the square footage may vary from the completed structure.

(from How to Measure a House by Ed Odham © 2005-2011) (704)-491-4862

Home Analytics
PO Box 680715
Charlotte, NC 28216-0012
Measuring a House

Per Ed Oldham from Charlotte, NC @ www.homeanalyticsappraisal.com