Ever wonder about how big your house really is? How many square feet (SF) of living space is in your house, and how does it compare to other homes in your own neighborhood?

You may have seen a SF number on a county tax card. You should also see it on the appraisal that the bank had to complete to finance your house. Your insurance agent either pulled a square foot number from the public record or got out his or her measuring tape and made their own calculations.

The square foot number on your house can be very important in determining the relative value of your home, how the taxing authority taxes you each year, and how much insurance you have to pay. Rather than just wonder about the size of your house, it would be helpful to know how to accurately measure your own house and be confident that the number you come up with is the number everyone else is using.

The most important number to know is your “heated” square footage. Heated is exactly the way it sounds – it’s the area inside your house that you control by heating (and cooling) it. The heated SF is where most of the value is derived from when comparing your house to other houses.

When an appraiser measures the exterior of your house, the appraiser will measure separately the improvements on the exterior of your house which are not heated square footage, such as decks, porches, garages, car ports, walkways, utility space, etc. The appraiser will also include in the measurements the interior spaces that are not finished or heated like unfinished basements, unfinished bonus rooms, unheated sun rooms (“Florida rooms”), storage areas, and mechanical rooms (areas in basement for hot water heater, heat exchanger, well tanks, etc.)

Another way to measure the base of your house is to measure the entire perimeter of the improvements, including around porches and decks, car ports, etc., then measure each improvement individually, and subtract those measurements from the original perimeter measurements. 

For instance, if you had a simple rectangular foundation which included a two car garage, you would measure the rectangle first, then measure the inside of the garage, and subtract the garage measurements from the rectangle to get the heated square footage.

It gets a little more complicated when you have to measure finished basements (partial or full), half-stories, lofts, second floors, landings, stairwells, finished bonus rooms, storage closets, etc. which must be measured from the INSIDE of your house. Real estate Appraisers have guidelines on how to measures spaces like these, which can be more exacting than those used by Tax Assessors or Insurance Agents. 

You can see adjustments made to value on an appraisal report based on these distinctions, including the terms “above grade” and “below grade”, which can be a bone of contention on an appraisal report for everyone including the homeowner. 

Also, the value given to heated square footage that is not part of the first floor base is typically lower per square foot, primarily because the main floor is the most expensive square footage to build, while finished basements and 2nd floors are less costly to construct per square foot.

An accurate measurement of the total heated and unheated square footage is an important number to know, and to get it right the first time you should call a certified residential appraiser and have an appraisal completed which includes sketches or diagrams of all the improvements on the property. The appraisal is also an opportunity to receive a fair market value of your home when compared to other similar recent home sales, especially if you have plans to sell your home in the very near future.