GLA and Measurement Standards · 6 min read

How to Measure a Condo for an Appraisal

Condominiums follow different measurement rules than detached single-family homes. The core difference: because a condo unit does not own its exterior walls, ANSI Z765 requires you to measure from the interior face of exterior walls — not the outside. If you apply single-family exterior measurement to a condo, you will overstate the GLA, which can create appraisal review flags.

The key rule: interior face of exterior walls

Under ANSI Z765-2021, for attached units (including condos, townhomes, and stacked flats), GLA is measured from the interior face of the exterior walls. For walls shared with another unit (party walls or demising walls), measurement goes to the centerline of the shared wall.

This is the opposite of the standard single-family rule, where you measure the exterior perimeter. For a condo, the unit owner only owns the airspace and interior — not the structure itself — which is why interior measurement is the correct basis.

Party walls vs exterior walls

Most condo units have a mix of wall types:

• Exterior walls (facing outside or a corridor) — measure to the interior face
• Party walls (shared with a neighboring unit) — measure to the centerline of the wall
• Interior walls (within your own unit) — do not affect the perimeter calculation; they are inside the measured area

In practice, for most condos, you will measure to the interior face on two or three sides (exterior-facing) and to the centerline on the remaining sides (unit-to-unit). The difference from a straight interior measurement is usually small but matters for accuracy.

Can I use the HOA floor plan?

HOA-provided floor plans are a useful starting point — many condo buildings provide dimensioned floor plans in the HOA documents or on the developer's website. However, you should verify those dimensions against your own measurement before relying on them for the appraisal.

Common issues with HOA floor plans:

• They may show nominal dimensions, not measured dimensions
• They may include exterior wall thickness, which overstates the interior area
• They may not reflect renovations or layout changes made by previous owners
• They may not be to scale (especially for older buildings)
• How to measure condo square footage
• Laser Measure vs Tape Measure for Floor Plans: Which Is More Accurate?
• GLA vs Total Square Footage: What Is the Difference?

Use the HOA floor plan as a reference for the room layout and overall shape, then verify the key dimensions on-site and reconcile against what you measure.

Assessor records vs appraiser measurement

County assessor records for condos are frequently inconsistent. Some assessors record the interior area, others record the exterior perimeter, and older records may be based on developer marketing materials. It is not unusual for an appraiser's measured GLA to differ from the assessor's record by 50–150 square feet on a typical condo.

When your measurement differs from the assessor record, note it in the addendum. Explain which methodology you used (interior face of exterior walls, centerline of party walls per ANSI Z765) and that your measurement controls. This is expected — you are not creating a discrepancy, you are correcting one.

What about balconies, terraces, and patios?

Balconies, terraces, and patios are not included in GLA under ANSI Z765 regardless of how they are configured. They may be noted separately as amenities and can contribute to value, but they do not count toward the square footage reported as Gross Living Area.

Similarly, common areas, lobbies, and hallways are not part of your unit's GLA — even if you use them constantly. Only the private interior of the unit counts.

Ceiling height requirements still apply

The same ANSI Z765 ceiling height requirements apply to condos as to single-family homes. To count as GLA, a space must have a ceiling height of at least 7 feet. For sloped ceilings, at least 50% of the floor area must clear 7 feet, and no area with a ceiling below 5 feet is countable at all.

This matters for lofts, mezzanine levels, and converted attic spaces within a condo unit. The same rules apply — no exceptions for condos.

Using PlanSnapper for condo measurement

If you have a floor plan from the HOA, developer, or an on-site capture tool like CubiCasa or iGUIDE, PlanSnapper lets you trace the perimeter to calculate GLA quickly. For condos, trace along the interior walls on the exterior-facing sides and the centerline of shared walls. Set your scale using a known dimension (a room length, a hallway width) and PlanSnapper will calculate the total area instantly.

You can also draw multiple polygons — useful when a condo unit has a complex shape, a storage unit on a different floor, or a loft level with partial ceiling height.

Related: What counts as GLA? · Exterior vs interior measurement · Ceiling height requirements for GLA · Why your measurement differs from the assessor