Retail Properties: ANSI/BOMA Z65.5-2020 Measurement Standards

Your Complete Guide to Gross Leasable Area

If you own, manage, lease, or appraise retail spaces - whether a neighbourhood strip mall, power center, lifestyle center, inline shops, banks, restaurants, medical clinics, or big-box anchors - Gross Leasable Area (GLA) is the single most important measurement for leasing clarity. It determines base rent, percentage rent, Common Area Maintenance (CAM) charges, property taxes, insurance allocations, and ultimately the property’s value.

The ANSI/BOMA Z65.5-2020 standard is the definitive rulebook for measuring retail properties in North America. It replaced older, less consistent methods and brought measurement and leasing clarity for renters and lessors, especially for mixed-use and public-facing spaces.

Here’s everything you need to know, explained in plain language.

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Gross Leasable Area (GLA) - The Measurement That Drives Everything

Gross Leasable Area is the total square footage a retail tenant actually leases and pays rent on. It is the foundation for almost every retail lease negotiation and valuation in Canada.

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Who Uses This Standard?

Any property that conducts business with the public should use ANSI/BOMA Z65.5-2020 as a guide for measurements. The standard applies to strip malls, shopping centers, freestanding retail buildings, banks, sandwich shops, medical offices, clothing stores, grocery anchors, pharmacies, salons, and more.

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Key Measurement Rule: Retail Walls Always Take Priority

Priority of retail unit walls is the most important practical rule in the entire standard:

Retail unit walls always take priority - both exterior and interior.
Measure to the exterior face of all exterior walls (including the full thickness of the wall and cladding).
For interior demising walls shared with another retail unit - measure to the centerline (midpoint) of the wall.
Retail space “wins” the wall thickness over common areas or service areas in virtually every case.

The retail walls rule almost always gives the landlord the maximum defensible GLA.

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Space Classifications - What’s In and What’s Out

Gross Leasable Rentable Exclusions (these are never included in a tenant’s GLA):

Parking Areas (surface lots, structured parking, garages)
Major Vertical Penetrations (stairs, elevators, escalators, flues, pipe shafts)
Service and Public Areas (common corridors, mall walkways, public restrooms, management offices, loading docks shared by multiple tenants)

Gross Leasable Areas (these are included in GLA):

Occupant Areas - the actual store, restaurant, clinic, or shop space the tenant controls and uses for business
Leased Kiosks - permanent or semi-permanent kiosks located in common areas that are leased to tenants

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Special Conditions Retail Owners & Tenants Must Know

Occupant Voids

Double-height sales floors, open-to-below areas, or dramatic two-story lobbies located inside a tenant’s space.

Fully included in the tenant’s GLA.

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Occupant Shafts

Tenant-specific vertical shafts for HVAC, plumbing, electrical, exhaust, or medical gases that serve only that one unit.

Fully included in the tenant’s GLA.

These two items often add hundreds (sometimes thousands) of square feet that were often disputed or excluded under older measurement methods.

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Practical Case Studies: How BOMA Z65.5-2020 Changes Outcomes

Case Study 1: Suburban Strip Mall Medical Tenant

A 5,800 sf urgent-care clinic argued it should be measured as “office” instead of retail.

Under Z65.5-2020:

Any space open to the public is considered to be Retail in the BOMA standard.
Walls take priority; Occupant Voids (double-height waiting area) and internal shafts are included.

Result: Landlord captured the full 5,800 sf as GLA instead of losing 400+ sf in negotiations — increasing annual CAM recovery and property value.

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Case Study 2: Lifestyle Center with Leased Kiosks

A regional mall has 18 leased kiosks in the common court.

Under the 2020 standard:

All kiosks are classified as Leased Kiosks and added to GLA.

Result: An additional 2,400 sf of billable area across the property with no additional construction that returned pure incremental income.

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Case Study 3: Freestanding Restaurant with Open Patio

A 4,200 sf restaurant includes a large covered patio used for seating.

Under Z65.5-2020:

The Occupant Area extends to the exterior face; qualifying covered areas are included.

Result: GLA increased by 850 sf, allowing the landlord to charge higher base rent without tenant pushback.

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Why Z65.5-2020 Still Matters in 2026

Even as newer 2025 updates roll out, the 2020 Retail Standard remains the most widely referenced and accepted version in leases, appraisals, and transactions across the U.S. and Canada. Its clear wall-priority rule, inclusion of occupant voids and shafts, and simple GLA focus make it landlord-friendly while remaining fair and transparent for tenants.

Using it correctly delivers:

Maximum (and fully defensible) leasable area
Fewer lease disputes and CAM arguments
Stronger property valuations and financing
Faster deal closings

Whether you’re remeasuring an existing strip center, negotiating a new medical-office lease, or valuing a lifestyle center portfolio, ANSI/BOMA Z65.5-2020 is the mandatory reference.

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See our companion pieces on methods of measurement for industrial spaces and office buildings if you found this quick guide helpful!

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Why Lessors and Commercial Tenants Trust UrbanMeasure

Need help applying BOMA Z65.5 rules to your property? At UrbanMeasure, accurate property measurement has been a core part of our work for over two decades. We are happy to review specific floor plans, walk through load-factor calculations, or work through GLAs and Gross Leasable Rentable Exclusions in a real retail property.

Our team specializes in hand-measured, professionally verified property measurements that comply with applicable measurement standards and reflect the conditions observed at the time of measurement.

In addition to measurement services, UrbanMeasure also provides:

By combining accurate measurement with high-quality visual marketing, we help real estate professionals present properties with clarity, confidence, and professionalism.

Stay accurate. Measure once, lease with confidence! Maximize Value!

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