What plumbing is involved in a commercial tenant improvement (TI)?

The plumbing in a TI follows the floor plan and the use. When a space changes hands, the old layout rarely matches the new tenant's needs, so fixtures get moved, added, or removed. A common scope includes new or relocated sinks, restrooms, drinking fountains, and the supply and drain lines that feed them.

Food service drives the biggest plumbing scope. A restaurant or cafe almost always needs floor sinks and floor drains, a grease interceptor, and a high-recovery commercial water heater. A floor sink is a recessed receptor that catches indirect waste from gear like ice machines and dishwashers. That gear does not drain straight to the sewer. It drains through an air gap above the sink, so dirty water can never get pulled back into the food equipment. The International Plumbing Code, Chapter 8, sets that air gap at "not less than twice the effective opening of the indirect waste pipe." Maricopa County also calls for food equipment to drain to floor sinks with at least a one-inch air gap.

Other common TI plumbing items include:

• A grease interceptor sized to the kitchen, or an upsized one if the old unit is too small.
• ADA-compliant restrooms with correct fixture heights and clearances (see below).
• Backflow prevention on the water service and on hazardous connections.
• A water heater matched to peak demand, often 140 degrees for sanitizing in a kitchen.
• New water, waste, and vent piping routed to the updated fixture locations.

Even a non-food tenant such as a salon, a medical office, or a gym has fixture and drainage needs that the prior layout will not match. The earlier this scope is mapped, the smoother the build.

For a restaurant, the grease interceptor is often the single largest plumbing item in the TI. Fats, oils, and grease cool and harden in the sewer. The EPA reports grease is the most common cause of sewer blockages, at about 47 percent of them. The interceptor traps that grease before it leaves the building. A small hydromechanical unit is sized by flow in gallons per minute. A larger gravity interceptor is sized by gallons, with a 750-gallon floor when the formula returns less. Many cities also require it be cleaned before it reaches 25 percent full of grease and solids.

Hot water is the other heavy lift. A commercial kitchen runs warewashers, prep sinks, and handwash sinks at once. The water heater has to keep up with peak demand, not average use. The FDA Food Code 2022 sets the temperatures that drive sizing. A handwash sink must deliver water at a set minimum temperature. High-temperature warewashing needs a final sanitizing rinse of at least 165 degrees for a stationary-rack machine and 180 degrees for other machines. A water heater that was fine for the prior tenant is often too small for the new one, so upsizing it is a frequent TI line item.

Handwash sink placement also matters. Maricopa County requires a handwash sink within 25 feet of food-prep and warewashing areas, so the plumbing rough-in has to land those sinks in the right spots before walls close up.

Most TIs trigger restroom work, and restrooms in a public commercial space must meet the 2010 ADA Standards. Those rules set hard numbers. The water-closet seat sits 17 to 19 inches off the floor. The lavatory rim is no higher than 34 inches, with knee and toe clearance and insulated pipes underneath so a seated user is not burned. Controls must work with one hand without tight grasping or twisting, at no more than 5 pounds of force. Getting these right at rough-in avoids tearing out finished walls later. For the full fixture-by-fixture breakdown, see our page on ADA commercial restroom plumbing.

Backflow prevention is a code condition, not an option. A cross-connection is any point where dirty water could get pulled back into the clean supply. Commercial buildings have many of them: irrigation, boilers, kitchen equipment, and more. Phoenix City Code 37-144 requires backflow assemblies to be tested every year by a certified tester. The results go to the Director and the Fire Marshal within 30 days. That testing is the customer's job. A high-hazard connection needs a reduced-pressure (RP) assembly, while a lower-hazard one may use a double-check valve. The right device is chosen by the degree of hazard, and it has to be installed and tested as part of the TI.

A commercial TI in Phoenix is not a same-day job. It runs through the city's permitting process. The City of Phoenix Planning and Development Department reviews commercial plans and issues permits before construction starts. A licensed plumbing or design team submits drawings, the city's plan review checks them against code, and only then does work begin.

The plumbing is inspected at two main stages. The rough-in inspection happens after pipe is run but before walls and slab cover it. The inspector checks pipe sizing, venting, slope, and the air gaps on indirect waste. The final inspection happens once fixtures are set and the system is running. Backflow assemblies are tested and certified in this window.

The last gate is the Certificate of Occupancy. A new tenant cannot legally open until the city signs off that the finished space meets code, and plumbing is part of that sign-off. What drives the timeline: plan-review turnaround, the size of the plumbing scope, whether the grease interceptor or sewer needs upsizing, lead times on commercial fixtures and water heaters, and how fast failed inspections get fixed. Food-service TIs take longest because they carry the most plumbing and a separate health-department review. If a kitchen is in the mix, our page on restaurant plumbing health-inspection requirements covers what the inspector looks for.

A frequent question on any TI is who owns and pays for the plumbing work, the landlord or the tenant. There is no single rule. It is set by the lease. A triple-net lease usually puts interior plumbing and the systems serving the space on the tenant, while the landlord keeps structural, central, and exterior items. A full-service or gross lease often leaves more with the landlord. The label matters less than the actual repair and build-out language in the signed lease, so read that clause closely before committing. Our page on commercial plumbing tenant vs landlord responsibility goes deeper on the split.

Early plumbing planning is where a TI budget is won or lost. The expensive surprises are the ones found after demolition or after the slab is opened: an undersized sewer line, no grease interceptor where a restaurant needs one, a water service too small for the load, or fixtures that fight the existing waste lines. Each one becomes a change order. That means new drawings, a fresh plan review, and idle days on the schedule. Bring in a plumber early, before the lease is signed if you can, so the real scope gets priced against the existing rough-in.

That early look is also why the contractor's license matters. A licensed contractor who works Phoenix commercial jobs knows local code, the city's submittal and inspection process, and the county food rules. Plans clear review the first time instead of bouncing back. HQ Plumbing and Air holds Arizona ROC #355170 and works commercial build-outs across metro Phoenix. Getting the plumbing scope, sizing, and permit path right at the start is the surest way to hit an opening date without a chain of costly change orders.