Calculating the Square Footage of a House

Date: 04/01/2004 at 07:06:06
From: Bonnie
Subject: general math

Is there an exact formula for finding the square footage of a house?

Date: 04/01/2004 at 12:40:02
From: Doctor Peterson
Subject: Re: general math

Hi, Bonnie.

I'm not sure there's a simple formula for that (in real life).  For a 
rectangular house, the area is the product of the length and the 
width.  But not all houses are simple rectangles, and there are also
rules for deciding which parts of a house count as part of the square
footage (e.g. the basement), or don't count (e.g. the garage).  And
multi-story houses can make it even more complicated.

Here is one place I found some rules:

  Measuring Houses and Counting Rooms
    http://www.chetboddy.com/Pages/measuringhouses.html 

  The total floor area of a house is one of the most important
  things a buyer needs to know.  But, until recently, there has been
  no national consensus on how to measure a house.  For years,
  architects, builders, real estate agents, lenders and appraisers
  have been using a hodge-podge of methods to estimate residential
  floor area.  In commercial real estate, where floor area is
  bought, sold and rented by the square foot, no one would tolerate
  this kind of vagueness and uncertainty.  In fact, standards for
  measuring office buildings have been in effect since 1915. ...

  In April, 1996 the American National Standards Institute (ANSI)
  adopted a standard for measuring single-family residential
  buildings. ...

  The ANSI standards base floor area calculations on the exterior
  dimensions of the building at each floor level, and include all
  interior walls and voids.  For attached units, the outside
  dimension is the center line of the common walls.  Internal room
  dimensions aren’t used in this system of measuring.

  The ANSI standards define “finished area” 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.”  Measurements
  must be taken to the nearest inch or tenth of a foot, and floor
  area must be reported to the nearest square foot.  Garages are
  specifically excluded.

The article gives a lot of detail on how to measure, what to include 
or exclude, and what to look out for.  It's not as simple as you'd 
think!

If you have any further questions, feel free to write back.

- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/