Until you have been involved in a litigation case that deals with the measurement of buildings you won't begin to appreciate just how little attention is often paid to the measurement process by builders, assessors and appraisal professionals.

Many residential appraisers will point you to the following definition for measuring buildings: Gross Living Area (GLA): "Definition: Total area of finished, above-grade residential space; calculated by measuring the outside perimeter of the structure and includes only finished, habitable, above-grade living space. Finished basements and attic areas are not generally included in total gross living area. Local practices, however, may differ."  Use: This definition is accepted by federal agencies for the measure single-family properties. Source: The Appraisal of Real Estate, Appraisal Institute, 12th Edition, Page 226).

Problems begin to crop up when people reference plans, marketing brochures prepared by builders, assessment information and other secondary sources and assert that they are accurate. 

One of the reasons that building measurement differences occur is that actual building measurements can be different from those that were planned. Architectual drawings are often close to actual, but appraisers often find that there are differences between the plans and the actual build-out.

Another reason for differences between a current measurement and past documents is that some buildings are changed. Many have had small or large additions, and some have seen partially or totally finished areas added within the previously unfinished garage.

How the building measurements are made provides a classic controversy for appraisers, builders and assessors. Many appraisers measure to 1/10th of a foot, as noted on their tapes or laser devices. Some round to the nearest foot, others round to the nearest 1/2 foot and finally some just don't round their measurements at all. Computerized drawing programs often are set to default to the nearest foot or 1/2 foot, so even if your measurements may have added 4/10ths of a foot across a 60 foot side of a building, the computer program that was used for the sketch may have inadvertently rounded off the 4/10ths making the buildings area smaller.

Commercial property appraisers often find that areas represented in leases do not measure actual areas.  When dealing with office condominiums, some owners will claim that common hallways, common baths or common reception areas are part of the square footage that they purchased, and the legal description may even include the common hallway.  

It is important to measure a building when it is appraised using a consistent technique and a measurement tool that you are familiar with, and it is important to remain consistent with regard to your rounding.  If you are in a metropolitan area, all of the appraisers won't be using the same technique, but finding out what your peers are doing is important.