Peppy Square

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The most commonly used formula for calculating square footage, and the one used by real estate appraisers, is to include only heated and air-conditioned areas of the house in the equation. That excludes the garage, attic storage, unfinished basements, porches, and any other such spaces.

The total square footage includes not only the areas of the rooms, but also the area occupied by the walls between the rooms. The area the walls occupy may seem small, only a few square inches, but it adds up fast. Three lineal feet of an interior wall equals one square foot. All totaled, the thickness of walls can be as much as ten percent of the overall square footage of the house.

You need to measure square footage from the outside faces of the outside walls and include the areas of the stairs. Count only spaces that have a ceiling height of more than seven feet. Stair areas count as a part of the floor from which they descend. Areas open to the rooms below do not need to be counted. Don’t worry about fireplaces, small mechanical closets, and such since these areas amount to a tiny fraction of the overall space.

Remember, the heated square footage is generally used in conjunction with a very rough estimate of the cost per square foot for preliminary cost estimating. It is one factor in the cost of construction, but it is not all that determines the actual cost of your house. There will be many costs that are unrelated to the size of the house, like appliances, landscaping costs, and the driveway, just to name a few.

Caution: Be sure the builder you are talking to defines “square footage” in the same way you do. Once in a while I run into a builder who wants to include the garage and porch areas. Or sometimes builders will count in the garage at half its square footage. This serves to “dilute” the overall cost per foot average. It can make the cost of construction seem lower, but it can make matters confusing. I prefer the appraiser’s method of counting the “heated square footage.”

Builders only use the “cost per square foot” as a rough estimate. They almost never sign a contract binding them to build a house at a particular cost per square foot. They’d go broke if they did that because there’s no way for them to know precisely what a home will cost until they know precisely what has to be ordered for the house and precisely how much labor it will take to build it. There are too many variables. You may want a stone exterior for your house. That will drive up the cost per square foot of your house considerably. Or you may want a certain kind of roof shingle that requires more labor and materials than a simpler one. That’s why some builders quote the estimated cost per square foot as a range. They won’t know precisely how much the house is going to cost until they know exactly how many and what kind of toilets, sinks, bricks, roofing material, appliances, flooring, and everything else that goes into the house will be required.