Every commercial lease negotiation eventually comes down to one deceptively simple question: who pays for what? A landlord quoting "$28 per square foot" and one quoting "$22 per square foot NNN" might land at nearly the same total cost — or a wildly different one — depending on which expenses are bundled into that number and which get billed separately. Understanding the three dominant lease structures, and the CAM charges layered on top of them, is the difference between an accurate budget and a nasty surprise six months into your build-out.
The Three Core Lease Structures
Commercial leases are generally grouped into a small number of recognized structures, and the trade association NAIOP (Commercial Real Estate Development Association) maintains official definitions for each in its published glossary of industry terms.
Gross Lease (Full-Service Lease)
In a gross lease, NAIOP defines the structure as one in which "a landlord receives stipulated rent from a tenant and is obligated to pay all the property's operating expenses and real estate taxes" (NAIOP, Commercial Real Estate Terms and Definitions). In plain terms: you pay one number, and the landlord handles property taxes, insurance, common area upkeep, and usually utilities out of that payment. This is the most predictable structure for a tenant's budget, but landlords typically price in a premium to cover their expense risk — gross leases have been shown to command rental rates roughly 15–25% higher than comparable net leases to compensate landlords for absorbing that variability (Century 21 Commercial, citing BOMA data on gross vs. net lease pricing).
Gross leases are most common in multi-tenant office buildings and are the standard structure for multifamily and other residential-style leasing, though they show up less often in ground-floor retail or restaurant space (J.P. Morgan Commercial Term Lending, What are CAM Charges in CRE).
Modified Gross Lease
The modified gross lease is the hybrid structure, and NAIOP defines it as "a lease in which the landlord receives a stipulated rent, and payment of the property's operating expenses is divided between the lessor and lessee via specified terms in the lease" (NAIOP, Commercial Real Estate Terms and Definitions). There's no single standard split — it's negotiated line-by-line. A common pattern has the landlord covering structural items, property taxes, and insurance while the tenant covers utilities, janitorial service within their own suite, or interior maintenance (Lextract commercial lease glossary). Because the split is custom to each lease, this is the structure where you most need to read the operating expense exhibit line-by-line rather than assume anything is included or excluded.
Triple Net Lease (NNN)
The triple net, or NNN, lease shifts the most cost and risk onto the tenant. NAIOP's official definition: "a lease agreement whereby the tenant pays taxes, maintenance and property insurance as well as all operating costs associated with the tenant's occupancy, including personal property taxes, janitorial services and utility costs. The landlord is typically responsible for the roof, HVAC, structure and sometimes the parking lot" (NAIOP, Commercial Real Estate Terms and Definitions). BOMA International's field guide describes the same structure as one where the tenant pays "all real estate taxes, building insurance, and maintenance (the three 'nets') on the property in addition to any normal fees that are expected under the agreement," while the landlord "assumes no costs, other than those for structural repairs or new installations" (BOMA International Field Guide glossary).
The name refers to the three "nets" stacked on top of base rent: property taxes, building insurance, and common area maintenance/operating costs. NNN is the dominant structure for single-tenant retail — commonly cited as the standard for freestanding restaurants, fast-food pads, and net-lease investment properties — and for industrial and big-box space (Rising Realty Partners, Triple Net Lease vs. Gross Lease). Base rent under NNN is quoted lower than under a gross lease precisely because the tenant is absorbing the operating cost variability — which means the quoted "rent" figure alone tells you very little about your actual monthly obligation.
Quick-Reference Comparison
| Feature | Gross Lease | Modified Gross Lease | Triple Net (NNN) Lease |
|---|---|---|---|
| Base rent structure | Single all-inclusive rent | Base rent + a negotiated subset of expenses | Lower base rent + taxes + insurance + CAM billed separately |
| Property taxes | Landlord pays | Negotiated — often landlord | Tenant pays (pro-rata share) |
| Building insurance | Landlord pays | Negotiated — often landlord | Tenant pays (pro-rata share) |
| CAM / operating expenses | Landlord pays | Split per lease terms | Tenant pays (pro-rata share) |
| Utilities (in-suite) | Often landlord, sometimes tenant | Usually tenant | Tenant |
| Structural repairs / roof / HVAC replacement | Landlord | Landlord | Landlord (typically) |
| Budget predictability for tenant | High | Moderate | Lower — costs shift year to year |
| Most common property types | Multi-tenant office, some multifamily-style retail | Suburban office | Single-tenant retail, restaurants, industrial |
Structure and property-type patterns per NAIOP, BOMA International, and J.P. Morgan Commercial Term Lending.
What CAM Charges Actually Include
Common Area Maintenance (CAM) charges are the shared costs of operating and maintaining the parts of a property that all tenants use — lobbies, hallways, parking lots, landscaping, elevators, and shared restrooms — and they're billed to tenants based on their pro-rata share of the property's total leasable square footage (Visual Lease, Unraveling Common Area Maintenance Charges). NAIOP folds CAM into its broader definition of "occupancy cost," which for a tenant "includes rent, their pro rata share of any operating costs (e.g., taxes, insurance, common area maintenance), personal property taxes and tenant insurance, and may include depreciation/amortization of tenant improvements" (NAIOP, Commercial Real Estate Terms and Definitions).
How CAM is handled depends entirely on your lease structure. In a gross lease, CAM is already baked into your flat rent. In modified gross, CAM might be split or capped by negotiated terms. In a triple net lease, CAM is billed on top of base rent, typically estimated and billed monthly, then reconciled annually against actual expenses (Allegro Realty, Gross Leases vs Net Leases vs Modified Gross Leases).
What Does CAM Typically Cost?
CAM and total operating expense figures vary significantly by property type, building class, and market — but industry benchmarking gives useful ranges. BOMA International's Office Experience Exchange Report, the most widely cited benchmark for office building operating costs, has historically placed average total operating expenses for U.S. private-sector office buildings in roughly the $8 to $9 per square foot per year range nationally, with high-cost gateway markets running well above that. BOMA's own 2018 report, for instance, showed New York City topping the list at $12.95 per square foot, while Salt Lake City sat at the low end near $6.02 per square foot (BOMA International press release on the 2018 Office Experience Exchange Report). A separate BOMA EER data point put total operating expenses at $8.07 per square foot with repairs and maintenance alone averaging $2.00 per square foot (FMLink summary of BOMA EER benchmarking data).
For retail, CAM tends to run lower per square foot than office but varies by center type. Industry benchmarking commonly cited by brokers places retail CAM at roughly $2 to $5 per square foot for strip and neighborhood centers, with anchored or lifestyle centers running higher due to landscaping, events programming, and shared parking upkeep (CAM Charges Calculator benchmarking data). Industrial and warehouse space, with minimal shared common area, typically runs the lowest, often under $1.50 per square foot (CalcBee CAM benchmarking data).
The practical rule: never take a quoted base rent at face value on a NNN deal. Ask for the trailing 12–24 months of actual CAM reconciliations, not just the landlord's current-year estimate, since estimates are trued up — and can increase — at year-end.
How to Estimate True Occupancy Cost
Whatever the lease structure, the number that matters for your budget isn't base rent — it's total occupancy cost. NAIOP's definition of occupancy cost is a useful checklist: rent, your pro-rata share of taxes/insurance/CAM, personal property taxes, tenant insurance, and any amortized tenant improvement costs (NAIOP, Commercial Real Estate Terms and Definitions). To build an apples-to-apples comparison across competing spaces:
- Start with base rent per square foot, annualized.
- Add your pro-rata share of CAM/operating expenses. Under NNN, get the landlord's actual trailing-year CAM history, not just a quoted estimate. Under gross or modified gross, confirm which expenses are truly included versus billed as "additional rent" for anything above a base-year amount.
- Add property taxes and insurance, if not already included in CAM, particularly under NNN and some modified gross structures.
- Add utilities not covered by the landlord — especially relevant for restaurant and medical concepts with heavy HVAC, water, or power draw.
- Add amortized tenant improvement costs and any landlord's operating expense caps or exclusions — the fine print in a modified gross lease often determines whether a repair bill lands on you or the landlord.
- Multiply by your square footage and divide by 12 for a real monthly number, then stress-test it against a scenario where CAM or taxes rise 5–10% year over year, which is common in reconciliation periods.
Questions to Ask Before You Sign
- What exactly is included in CAM, and is there a cap on annual increases? Ask for the specific list of included/excluded expense categories, not just the word "CAM."
- Can I see the last two years of actual CAM reconciliation statements, not just the current estimate?
- Who is responsible for HVAC replacement, roof repair, and structural issues — and is there a cap on how much of a major capital repair can be passed through to tenants in a single year?
- Is there a base year, and how are increases above it calculated, if this is a gross or modified gross lease?
- What's my pro-rata share formula — is it based on my square footage over the whole building's rentable area, or some other method, and is that documented?
- Are there any exclusions for landlord negligence or capital improvements that shouldn't be passed through as an operating expense?
- What's the term length and renewal structure, and how does that affect my ability to negotiate CAM caps or expense audits later?
The Bottom Line
There's no universally "cheaper" lease type — a NNN deal with low base rent but high CAM and a fully unpredictable tax/insurance pass-through can cost more than a straightforward gross lease, especially in older buildings with deferred maintenance. The only way to know for certain is to model total occupancy cost, not just headline rent, before you sign. Many operators build that model in a spreadsheet alongside their build-out budget; some newer platforms, including BuildoutIQ, are designed specifically to combine build-out cost estimates with projected occupancy costs so you can compare space options on a true monthly-cost basis rather than rent-per-square-foot alone.
