Guides · Floor Plan Measurement
Townhouses have two characteristics requiring attention: multiple floors and shared party walls. Both are straightforward to handle once you understand the conventions. This guide covers the complete process for measuring townhouse GLA accurately.
Like any multi-story home, measure each above-grade floor as a separate polygon. Ground floor, second floor, and any additional floors each get their own trace. Sum all above-grade finished floor polygons for total GLA. Upload each floor plan separately and recalibrate scale from each image.
When two townhouse units share a wall, the common convention is to measure to the centerline: half the wall thickness attributed to each unit. In practice: the exterior wall facing the street or rear is traced at its true exterior face. The shared wall(s) facing adjacent units are traced at the wall centerline. Most digital floor plan exports (CubiCasa, Matterport) draw the unit boundary at approximately the centerline already. For hand-drawn sketches showing full party wall thickness, trace to the centerline.
End units have a "true" exterior wall on one side (measured to exterior face) plus the shared walls on the other side (measured to centerline). Interior units have shared walls on both sides. End units are typically slightly larger than interior units of the same nominal design because one side is measured to the full exterior face rather than the centerline.
Many townhouses have a ground-floor garage or a finished lower level. Trace the garage as a separate polygon: it's not GLA. A finished below-grade level is also not GLA. Some townhouses have a ground floor that's part garage and part living space; trace only the living space portion in your GLA polygon.
Townhouses often have staircase voids on upper floors: no floor exists above the stair run. When tracing upper floors, exclude this void by placing polygon points at the corners of the void and indenting the polygon around it. The tool handles these concave shapes correctly.
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Start Measuring →How do I measure a townhouse from a floor plan?
Trace each floor of the townhouse as a separate polygon (typically two to three floors), set scale from any labeled wall dimension, and the tool sums the floors for total GLA. Most townhouses use the wall-centerline convention for shared party walls.
What is the wall centerline convention for shared walls?
On shared (party) walls between adjoining townhouse units, the convention is to measure to the centerline of the shared wall, splitting the wall thickness equally between units. This is the standard ANSI approach for attached units and what most appraisals use.
Should I trace each floor separately?
Yes. Each floor is a separate polygon. The tool sums them for total GLA. Tracing all floors as one combined polygon would double-count the shared footprint.
Are party walls included in townhouse square footage?
Half of each party wall's thickness (the centerline convention) is included in your unit's GLA. The other half belongs to the adjoining unit. This is the standard appraisal approach.
How is townhouse GLA different from single-family GLA?
The methodology is identical, but the wall-centerline convention applies to shared walls (which single-family homes don't have). End-unit townhouses use exterior measurement on the non-shared sides and centerline only on the party wall.