Base Building vs Tenant Work: What Am I Actually On the Hook For?

The rule of thumb that settles most arguments

The single test that resolves nearly every base-building-versus-tenant-work dispute is this: anything that benefits the building long-term and outlasts your tenancy is the landlord's; anything that exists only because of your specific use is yours. The structure, the envelope, the core mechanical plant, and the utility service feeding your suite are permanent assets on the landlord's balance sheet. Your offices, conference rooms, paint colors, supplemental cooling, specialty power, and equipment are tenant improvements — they leave (or get demolished) when you do.

That framing matters because it tells you who *should* pay under standard commercial real estate practice, which is the leverage you use at the negotiating table. When a landlord tries to slide a structural repair or a core-system cost into your tenant-improvement (TI) scope, you name it for what it is: their building, their permanent asset, their cost. The clean cases are easy. The foundation, columns, floor slab, roof membrane, and exterior walls are unambiguously base building. Your carpet, your millwork, your branded reception wall, and your desks are unambiguously yours.

The problem is that a commercial buildout has dozens of line items, and a meaningful share of them sit on the *seam* between shell and fit-out. Those boundary items — HVAC distribution, sprinkler drops, electrical branch circuits, restroom construction — are where budgets blow up, because every item you fail to define in writing quietly defaults to the tenant. The rule of thumb tells you where each item *belongs*; the work letter is what makes it stick. Treat the rule as your argument and the written delivery-condition exhibit as your proof.

The base building / tenant work line, item by item

Use this as a negotiation checklist and confirm each item lands where it should before you sign.

Landlord / base building — push to keep these theirs:

• Structure — foundation, columns, floor slab, and roof structure.
• Envelope — exterior walls, windows, roof membrane, and weatherproofing.
• Core HVAC — the rooftop unit (RTU) or central plant and the main trunk duct to your suite.
• Primary electrical — service to a panel in or near your suite at a defined amperage.
• Base plumbing — main water, sewer, and a code-compliant common or in-suite restroom.
• Life-safety base — the building fire-sprinkler main and risers, the fire-alarm panel, and exit stairs.
• Accessible path of travel to your suite entry door.

Tenant / TI work — expect to pay for these:

• Interior partitions, doors, and finishes — flooring, paint, ceilings, and millwork.
• HVAC distribution — branch ducts, variable-air-volume (VAV) boxes, diffusers, thermostats, and balancing.
• Electrical distribution — sub-panels, outlets, your lighting, and low-voltage and data cabling.
• Sprinkler drops and head relocation to match your ceiling layout.
• Specialty systems — supplemental cooling for a server room, a grease interceptor, or special power.
• Signage, security, and branding.

The clean items rarely start a fight. What starts a fight is a one-line lease clause like "HVAC provided" or "electrical to the suite" that reads like a complete deliverable but actually stops at the base-building boundary. The checklist's job is to force each ambiguous item into either the "landlord provides and installs" column or the "tenant scope" column so nothing lives in the fog in between.

HVAC: the single most expensive ambiguity

If you learn one thing before signing, learn how the landlord defines "HVAC provided." Landlords love that phrase because it's technically true and practically misleading. It usually means the base-building rooftop unit and the main trunk duct exist — the heavy, permanent equipment sitting on the roof and the primary duct dropping into your suite. What it very often does *not* include is distribution: the branch ductwork, diffusers, thermostats, VAV boxes, and air balancing that actually push conditioned air into your specific floor plan.

Distribution is tenant work, and it runs significant cost depending on your market, ceiling height, and layout complexity. On a 4,000-square-foot suite this can represent tens of thousands of dollars you may never have budgeted because you read "HVAC provided" as "HVAC done." A landlord who delivers a "capped duct at the suite" has handed you a single stub — everything downstream is yours to design, permit, install, and balance.

Two numbers pin this down. First, confirm tonnage: office space typically needs roughly one ton of cooling per 300 to 400 square feet, and a landlord who delivers less than that has undersized your space before you've hung a single light. Second, confirm who balances the system — a distributed but unbalanced system produces the classic complaint of one conference room at 62°F while the corner offices bake. Ask directly: does the landlord deliver HVAC *distributed and balanced* to your approved plan, or just the unit on the roof? Put the answer in the delivery-condition exhibit, because on this one item the difference can be tens of thousands of dollars.

The other boundary items that decide your budget

HVAC gets the headline, but three more seam items routinely surprise tenants who thought the shell was "basically done."

Electrical capacity. Get a stated amperage and voltage delivered to your suite in writing. A landlord who promises "electrical to the suite" without a number may be handing you a panel that can't carry your load. Discovering you need a service upgrade — pulling new feeders from the building's main switchgear — can be a significant surprise cost. The landlord typically provides the main panel (often 100-amp or 200-amp); everything past it — branch circuits, outlets, switches, and specialty power for a lab, kitchen, or server room — is yours. If you need a 400-amp service for equipment, negotiate for the landlord to fund the *service upgrade* even while you pay for the internal distribution.

Fire sprinklers. The base building provides the sprinkler main and risers; relocating heads and drops to fit your ceiling grid is tenant work. An open, undeveloped ceiling means you're covering the whole grid.

Restrooms, floors, and ceilings. Confirm whether code-compliant restrooms are delivered or whether you're building them — that alone can escalate fast under ADA requirements. Confirm the slab is delivered level and sealed, and whether a ceiling grid exists or you're buying it. "Open to deck" means no ceiling at all. And nail down the shell definition itself: a "cold shell" (bare — no HVAC distribution, no restrooms, no ceiling), a "warm shell" (HVAC, restrooms, and basic systems roughed in), and a "turnkey" delivery (landlord builds to your plan) describe wildly different starting points and wildly different budgets. Know which one you're actually buying.

What "vanilla box" and "warm shell" really mean

Landlords use "vanilla box," "white box," and "warm shell" loosely, and rarely define any of them the same way twice. A true vanilla box typically includes four painted walls (one coat, builder's white or light gray), a raw concrete floor (no polish or sealer), a dropped ceiling with standard 2×4 acoustic tiles and basic LED troffers, one restroom or a stub-out for future restroom construction, a single electrical panel (100 to 200 amp with no branch circuits), and one HVAC supply and return with no ductwork beyond the main trunk.

Anything past that — upgraded flooring, better lighting, additional restrooms, a kitchenette, data cabling, or specialty walls — is tenant improvement work. A "white box" or "warm shell" may push a little further (carpet tiles, a handful of outlets), but it's still far from move-in ready. The names are marketing; the exhibit is contract.

The protection is procedural: demand a written "scope of landlord's work" exhibit attached to the lease, listing every item the landlord will provide and install before you take possession. Ask your architect or tenant rep to mark the exact "point of connection" on the lease drawings — the single line where the landlord's duct, conduit, and pipe stop and yours begin. That one drawing, plus the scope exhibit, converts a vague adjective into an enforceable deliverable and saves you thousands in "we assumed that was included" arguments after you've signed.

The hidden costs that catch tenants off guard

Even experienced tenants get surprised by three categories that fall squarely on their side of the line and rarely show up in the landlord's TI allowance.

Data and low-voltage infrastructure. Running CAT6 cable, fiber, security cameras, access-control wiring, and Wi-Fi access points is entirely tenant work. A 5,000-square-foot office with 40 drops can easily run thousands of dollars — a line item that never appears in the shell description because it isn't part of the shell.

Permitting and impact fees. Your tenant-improvement permit is your responsibility. In high-cost cities, permit fees alone can be significant for a moderate buildout, and some municipalities layer on transportation or other impact fees keyed to square footage. These are almost never covered by the landlord.

Furniture, fixtures, and equipment (FF&E). This is the biggest blind spot. Desks, chairs, filing cabinets, conference tables, breakroom appliances, window treatments, and signage are 100% tenant cost. If you're taking a "fully furnished" space, verify exactly what stays and get it in writing. The practical takeaway: add a buffer to your initial TI estimate for these off-shell items, because your landlord's allowance almost certainly won't.

How to shift boundary items onto the landlord

The whole game is moving seam items onto the base-building side and funding the rest with the landlord's money.

• Make the landlord define the delivery condition in detail. A one-line "warm shell" isn't enough. Demand a delivery-condition exhibit listing exact HVAC tonnage and distribution, electrical amperage, sprinkler coverage, restroom status, and floor and ceiling condition. Every item you nail down is one that can't silently become your cost.
• Use the TI allowance for permanent systems. HVAC distribution, electrical sub-panels, and sprinkler work are permanent building improvements — fund them from a tenant-improvement allowance, not your own capital.
• Negotiate a base-building warranty. Insist the landlord warrants that the roof, structure, core HVAC, and base electrical are in good working order at delivery. If the rooftop unit dies three months in, that's the landlord's repair, not your emergency.
• Cap your exposure with a turnkey deal. In a tenant-favorable market, push for turnkey — the landlord builds to your approved plan at their cost, capped at an agreed budget, and you stop carrying construction risk entirely.
• Carve base-system repairs out of your operating costs. Make sure the lease puts structure, roof, and core HVAC repair and replacement on the landlord rather than burying them in your common-area maintenance (CAM) charges.
• Get an independent shell inspection. Before signing, have a contractor verify the actual condition matches the promised delivery. A landlord's "warm shell" sometimes hides a dead RTU or an undersized panel — and it's far cheaper to find that before the lease binds you than after.

FAQ

What exactly counts as "base building" in a commercial lease? Base building typically includes the structural shell, core columns, exterior walls, roof, and major systems like the main HVAC unit, elevators, and fire risers. The landlord must deliver these in working order, but anything you add or modify inside your space is your cost.

Who pays for electrical outlets and data cabling in my office? You do — these are tenant improvements, not base building. The landlord provides the main electrical panel and the data riser to your floor, but all distribution wiring, outlets, switches, and low-voltage cabling inside your suite are yours to design, permit, and install.

Am I on the hook for repairing the HVAC serving my space? It depends on the lease. In a gross lease the landlord usually handles HVAC repairs; in a triple-net (NNN) lease you may own maintenance and repair of the unit serving your suite. Read exactly how the lease assigns "HVAC maintenance" before you sign.

What does "HVAC provided" usually mean? Typically only the base-building rooftop unit and the main trunk duct — not the branch ducts, diffusers, thermostats, and VAV boxes that distribute air into your layout. That distribution is tenant work, so confirm whether the landlord delivers a balanced, distributed system or just the unit on the roof.

Can I deduct the cost of tenant work from my rent? Generally no. Direct rent deductions for buildout costs are rare and not standard practice. Instead, negotiate a rent-abatement period (commonly two to six months of free rent) to offset construction time, or push for a larger tenant-improvement allowance.

How much should I pad my TI budget for hidden costs? Add roughly 15 to 20% on top of your base estimate for items the allowance rarely covers — data and low-voltage cabling, permits and impact fees, and furniture, fixtures, and equipment. These are entirely tenant costs and routinely blindside first-time tenants.

What happens to my improvements when the lease ends? Unless the lease says otherwise, built-in improvements — walls, flooring, custom millwork — usually become the landlord's property, and you may be required to remove them and restore the space to base-building condition. Negotiate a removal clause that limits or waives that restoration obligation.

Sources

• BOMA International — https://www.boma.org/
• CBRE Research — https://www.cbre.com/insights
• JLL Research — https://www.jll.com/en-us/insights
• Cushman & Wakefield — https://www.cushmanwakefield.com/en/united-states/insights
• Gordian (RSMeans construction cost data) — https://www.gordian.com/
• NAIOP — https://www.naiop.org/
• International Code Council (International Building Code) — https://www.iccsafe.org/
• U.S. Access Board (ADA standards) — https://www.access-board.gov/

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