In commercial real estate, the dollar amount a tenant pays for rent is just the beginning of the story. The real question is: who pays for the building's operating expenses? Property taxes, insurance, security, janitorial services, landscaping, and HVAC repairs all cost money. How these costs are divided between the landlord and tenant is defined by the lease's expense recovery structure.

This structure determines how predictable a landlord's income will be and how much risk each party is taking on. Let's break down the most common ways these expenses are handled.

The simplest structure, from the landlord's perspective, is the Triple Net (NNN) lease. Here, the tenant is responsible for paying not only the base rent but also their pro-rata share of the building's three main operating expenses: property taxes, property insurance, and common area maintenance (CAM). Think of CAM as the costs for all shared spaces—lobbies, parking lots, elevators, and hallways.

For landlords, this is a highly attractive setup. It creates a predictable, passive income stream because the major variable costs are passed directly to the tenants. If property taxes or heating costs suddenly spike, the landlord's net income isn't affected. This structure effectively isolates the landlord from expense volatility. The trade-off is that the base rent in a NNN lease is typically lower than in other lease types, since the tenant is shouldering a larger portion of the total occupancy cost.

A slight but important variation is the Absolute NNN lease, which takes the tenant's responsibility a step further. In these leases, the tenant pays for literally everything, including major structural repairs to the roof or foundation. They are often used for single-tenant, freestanding buildings occupied by a credit-worthy national chain, like a Walgreens or a McDonald's.

On the opposite end of the spectrum is the Full-Service Gross (FSG) lease. Here, the tenant pays one flat rental rate, and the landlord is responsible for paying all the building's operating expenses. This structure is common in large, multi-tenant office buildings where dividing up utility and service costs among dozens of tenants would be an administrative nightmare.

While simpler for the tenant, a gross lease introduces significant risk for the landlord. If operating costs rise unexpectedly, the landlord's profit margin shrinks. To protect themselves, landlords often use a mechanism called an Expense Stop or establish a "Base Year."

With an Expense Stop, the landlord agrees to pay operating expenses up to a certain amount, for example, $8 per square foot. Any costs above that amount are passed on to the tenant. A Base Year works similarly. The operating expenses from the first year of the lease (the "base year") set the benchmark. In all subsequent years, the tenant pays for any increases in expenses over that base amount. This creates a Modified Gross (MG) lease—a hybrid that shares the risk of rising costs.

For example, if the base year expenses are $100,000 and they rise to $110,000 in year two, the tenant would be responsible for paying the $10,000 overage.

Different lease structures make it difficult to compare offers directly. A $25/SF Gross lease might sound more expensive than an $18/SF NNN lease, but that's not the full picture. To make an informed decision, you must calculate the effective rent—the all-in cost of occupancy.

Let's compare two hypothetical offers for a 2,000 square foot space:

In this scenario, the NNN lease is actually more expensive once the additional expenses are factored in. However, the analysis doesn't stop there. In Building B, the tenant is protected from expense increases only in the first year. If property taxes or utility costs are expected to rise sharply, the Modified Gross lease could become more expensive over time.

Ultimately, choosing a lease structure involves a trade-off between the base rent amount and the risk of future expense volatility. Landlords want predictable income, and tenants want predictable costs. The final lease agreement reflects how these two parties agree to share that risk.