Short answer: commercial repairs are contract-driven, not statute-driven. Who pays turns on the lease type. A triple-net (NNN) tenant typically pays taxes, insurance, CAM, and often repairs on top of base rent. A gross (full-service) landlord folds those costs into one rent number and is the default payer. Modified gross splits expenses by negotiation, with no fixed default. Commercial tenants also get far weaker statutory protection than residential tenants, the repair clause in your lease controls, not the label on it.
NNN vs. gross vs. modified gross
Cornell's Wex legal dictionary defines a triple net lease as one where "the lessee pays rent and utilities as well as three other types of property expenses: insurance, maintenance, and taxes," and its net lease entry says the rent can sometimes extend to "other costs such as utilities or repairs." A gross lease runs the opposite way:
"In a gross lease, the landlord includes maintenance fees, taxes, and other expenses in their calculation of the rent."
Cornell Law School, Wex
Modified gross sits between the two, Investopedia calls it a structure that "uniquely blends elements of both gross and net leases, sharing operating expenses between landlords and tenants." None of these labels are standardized by law; the actual expense-allocation schedule governs, not the lease's name.
HVAC, roof, and structure
HVAC responsibility doesn't follow who owns the equipment: "the commercial lease determines how HVAC repair costs are allocated; the landlord is not automatically the final payer simply because the equipment belongs to the building," per one commercial real estate blog. A lease can route routine repair one way and capital replacement another, read those clauses together.
Roof, foundation, and load-bearing walls stay with the landlord more consistently, even in many NNN deals:
"Structure. Walls, foundation, load-bearing elements. These should never be the tenant's responsibility. But vague maintenance language can create exposure here, particularly in older buildings."
The Leasing Lawyers
Watch for boilerplate like "tenant responsible for all repairs," which can be read broadly enough to sweep in structural items. Confirm roof and structure are explicitly carved out to the landlord in writing.
CAM charges
Common Area Maintenance (CAM) is how tenants in net and NNN leases reimburse the landlord for shared costs, "the operating costs associated with running the shared areas of a building or shopping center," including landscaping, parking lots, exterior lighting, common hallways, and trash removal, per one leasing-law resource. CAM definitions are negotiated line by line and can run broad, get the definition and any caps in writing before signing.
Tenant improvements, ADA, and habitability
Who pays to build out the space, landlord turnkey, a negotiated tenant-improvement allowance, or a tenant-funded fit-out, is a deal point, not a default rule; it depends on lease structure and market leverage. Whether the tenant must undo the build-out later is a separate question, governed by the surrender clause.
ADA is the one place a federal rule sits above the lease. Under the DOJ's ADA Title III regulations, both the "landlord who owns the building" and "the tenant who owns or operates the place of public accommodation" are:
"public accommodations subject to the requirements of this part. As between the parties, allocation of responsibility for complying with the obligations of this part may be determined by lease or other contract."
28 CFR § 36.201(b), U.S. Department of Justice
Both are independently on the hook to the government, which can pursue either one. A lease can allocate who pays for ramps, doorway widening, or accessible restrooms, but that private allocation doesn't bind the DOJ or the public.
Commercial tenants also don't get the residential safety net: the implied warranty of habitability "applies to residential leases," per Cornell's Wex, and generally does not extend to commercial space, which is why the written lease matters so much more here.
Repairs at lease-end (surrender)
At lease-end, the burden generally shifts back to the tenant: "Generally, the tenant is responsible for all costs associated with meeting the surrender obligations, including removal of alterations, repair of damage, and cleaning," per one commercial leasing law firm, and if not, "the landlord often reserves the right to perform the work." Even with no removal language, tenants typically must still meet the surrender standard, often "good condition or broom-clean, ordinary wear and tear excepted". That scope should be checked, and negotiated, before signing.
The lease controls
NNN, gross, and modified gross are common patterns, not guarantees, read the actual repair, maintenance, CAM, and surrender clauses before assuming who pays for a roof leak, a dead rooftop unit, or an ADA upgrade. Start with the lookup tool, or ask a specific question through the who-pays concierge.
This is general information, not legal advice. Commercial lease outcomes are set by the lease itself, not a general statute. Have your specific lease reviewed by a qualified attorney before relying on any pattern described above.