Medical Office Building CAM: What Counts as 'Common Area' in a MOB?
In a standard retail or office building, the definition of common area is usually clear: the lobby, hallways, restrooms, parking lots, and exterior spaces used by all tenants. A medical office building (MOB) is more complicated.
MOBs often include a mix of tenant-specific improvements, shared patient waiting areas, specialized corridors, imaging suites, procedure rooms, and support spaces that do not fit neatly into standard CAM definitions. What counts as "common area" for CAM purposes in your building depends primarily on what your lease says, but the landscape of disputes around this question is significant.
Here's what to know.
Spaces that are always considered common area
These categories are unambiguous in virtually every commercial lease, including MOB leases:
Main lobby and building entrance. Shared by all tenants and their patients. CAM inclusion is standard.
Primary corridors and hallways. Interior circulation paths used by all tenants. CAM inclusion is standard.
Elevators and stairwells. Shared vertical transportation and egress. CAM inclusion is standard.
Parking lots and access roads. Unless your lease specifically provides a parking area exclusive to your practice, the parking lot is common area. CAM inclusion is standard.
Public restrooms. Restrooms accessible to building visitors and patients in general, not specific to any tenant suite. CAM inclusion is standard.
Exterior building maintenance areas. Loading docks, mechanical rooms, trash enclosures, and utility connections serving the whole building. CAM inclusion is standard.
These spaces rarely generate disputes because their common-area status is obvious.
Spaces that are sometimes contested in MOBs
This is where MOB disputes concentrate. Medical office buildings often have specialized spaces whose common-area status is genuinely ambiguous.
Secondary waiting areas and patient holding areas. If your building has a shared secondary waiting area or patient staging area used primarily by tenants in one wing or one specialty, some landlords include this in CAM. If the space is truly shared by all tenants, that may be legitimate. If it primarily serves a subset of tenants, its inclusion depends on whether your lease broadly defines common area to include such spaces.
Imaging suite corridors and shared diagnostic spaces. MOBs with shared imaging equipment (MRI, CT, X-ray) may have corridors, waiting areas, and support spaces associated with that equipment. Whether those spaces are common area depends heavily on whether you have access to and benefit from the imaging services. A dental practice in the same building as a radiology suite that it does not use has a reasonable argument that imaging-corridor-related costs should not appear in its CAM.
Medical gas manifold rooms and mechanical spaces serving specific tenants. A medical gas room serving surgical suites or procedure rooms for specific tenants is arguably not a common area if you are a general practice tenant who does not benefit from those systems. Whether it belongs in CAM depends on your lease's definition.
Covered parking or reserved physician parking areas. If the building includes covered or reserved parking that is not equally available to all tenants, including those areas in the CAM denominator or the CAM expense pool may overstate your obligation.
Here's the critical point: your lease's CAM definition controls. Broad definitions ("all areas maintained by landlord for benefit of tenants generally") can pull in many of these contested spaces. Narrower definitions that enumerate specific categories provide more protection.
What your lease's CAM definition controls
Find this language in your lease: the definition of "operating expenses," "common area maintenance," or "CAM expenses." Read it carefully for two things:
What is expressly included. Some leases enumerate specific space types or expense categories that are included.
What is expressly excluded. Most well-drafted MOB leases include an exclusions list. Common exclusions include costs for tenant-specific improvements, capital expenditures, costs covered by insurance, and expenses for vacant or unleased spaces.
If a space is not expressly included or excluded, you are in interpretation territory. That is where disputes arise and where the specific wording of your lease matters most.
What to request when you think your MOB is overcounting common area
Request the following from your landlord in writing:
- A floor plan or building diagram showing how common area square footage was calculated
- The breakdown of which spaces are classified as common area versus tenant space
- The total gross building area, total tenant leasable area, and total common area square footage
- Your pro-rata share calculation using these figures
If the landlord cannot or will not provide a clear explanation of how common area square footage was calculated, that is itself a signal worth noting in any future dispute.
Your audit window is typically 60 to 180 days from the reconciliation delivery date. Send your documentation request before that window closes.
Getting a clear answer on your specific situation
MOB CAM disputes are more complex than standard retail or office disputes because the space types are more varied and the lease definitions matter more. The free scan at CAMAudit includes checks for common area misclassification, pro-rata share calculation errors, and expenses that do not belong in a standard CAM pool.
Upload your lease and reconciliation statement and the tool will flag potential issues tied to your actual lease language. If you are in a multi-tenant MOB with contested spaces, that analysis is worth having before you decide whether to pursue a dispute.
Read next: Medical Office CAM Charges | Pro-Rata Share Errors in CAM Reconciliations | Common Area Misclassification in Commercial Leases