I have been using the below in my Limiting Conditions since about 2005 (with a few minor additions for the current FNMA/ANSI changes):
"LIMITING CONDITION #2 COMMENTS: STANDARDS FOR LIVING AREA MEASUREMENTS & FLOORPLAN DIMENSIONS
- ANSI Standard Z765-2021 is followed for measuring the living area of single-family residential buildings. The ANSI standard allows for circumstances that can exist where direct measurement of a structure is not possible. Access to the interior may not be available and the nature of the terrain, structure, or other obstacles may preclude direct physical measurement of the exterior in the time available. Building dimensions developed through some means other than direct measurement or plans can be susceptible to inaccuracy, as is the calculated area. Calculation of square footage developed under such circumstance will be identified as such when reporting the result of the calculation. The finished square footage of a house is to be reported to the nearest whole square foot for above-grade finished square footage and for below-grade finished square footage.
- MEASUREMENTS: Measurements are done to the nearest 1/100th of a foot, but reported to the nearest 1/10th of a foot per ANSI requirements. That is to say, dimensions on the floor-plan are in fact to the nearest 1/100th of a foot, but rounded to 1/10th of a foot in the displayed floor-plan dimensions.
- AREA CALCULATIONS: The actual calculation of the living area usually involves entering the measurements as a floor plan into the CAD software program Chief Architect, and letting it calculate the enclosed Gross Living Area, as well as other building areas. This is appropriate since many homes have floor-plans that are otherwise to difficult to manually calculate area for. Chief Architect uses a discrete version of Greens theorem to do this. The procedure is to perform “Make Polyline” on the exterior walls then “Open Object” on the resulting polyline. This displays the enclosed area. Open areas, garages spaces and utility areas can be similarly calculated and the resulting values subtracted from the Gross Floor Area to obtain the Gross Living Area.
INTERIOR MEASUREMENTS: Room placement and interior wall measurements allow judgment as to the appropriateness of a floor plan for a given buyer profile. So, it is considered important to show these as accurately as possible in floor-plans. Typically, reported interior wall measurement accuracy to within 1/10th a foot is considered adequate for most rooms. However, some rooms and especially closets may be too cluttered to take accurate estimates. Also, particularly in older homes, there may be hidden spaces between walls and double or extra thick walls that cannot be accurately measured. All interior measurements plus estimated wall thickness should add up to exterior dimensions. In fact, this is required by the CAD system. Consequently, to make the interior measurements reconcile to exterior measurements, sometimes slack has to be allowed. Some room dimensions may need to be extended or "slack" areas created. This should be indicated on the floor-plan as "SLACK". E.g. 10.5' (includes SLACK), -or the display of a "virtual" room called "SLACK".
- Differences to Tax Assessor Values: Tax assessor reported measurements are often derived from architectural building plans, which do not follow the ANSI standard. As such, they may differ from reported measurements done per ANSI. Also, contractors often deviate from the original plans as presented to assessors, so that the finished square footage of the house as built may be quite different than reported by the tax assessor. "
NOTES:
1. Chief Architect/Home Designer Pro allows you to put in measurements to whatever accuracy you desire, but then specify a different accuracy for what is displayed on the floor plan. So, although it seems a contradiction, your actual CAD measurements can be in 1/10,000 of a foot, - while what is displayed is only the value rounded to the nearest 1/10th of a foot. In fact, if you hover the cursor over the measurement in the CAD you will see the underlying more precise measurement. --- PERFECT!!
2. The actual GLA calculations are done in an Improvements Addenda - where problems specific to the subject property are reported.
3. Lot Sizes and property maps are a whole different ballpark.
