For: Operators planning to add training floor or stations, and the dealers and designers scoping the project.
The decision: Whether the next dollar goes into more equipment and floor, or into the changing rooms, plumbing, ventilation, power, parking or staffing that would limit the expanded floor.
60-second answer: More exercise area can raise the occupant load the code official calculates, and occupant load drives plumbing fixture counts, while the mechanical code’s design occupancy drives ventilation. Model codes set the method; the locally adopted code sets the numbers. Michigan, for example, adopts the 2021 International Plumbing Code with state amendments, and Michigan’s amended Table 403.1 lists gymnasiums at 1 water closet per 125 male and 1 per 65 female occupants. The ADA Standards add requirements for showers, lockers and locker rooms where they are provided, and an alteration to a primary function area brings the restrooms on its path of travel into scope. Measure each constraint at peak, have the architect run the code calculations, and size the equipment order for the limit that binds first.
Why more floor can mean more building work
A gym expansion equipment order relieves the station queue and moves it to the next limit in line: the shower, the locker, the air, the circuit, the parking lot or the supervision of the new zone. Some limits are operational. Others are set by the codes your jurisdiction has adopted, as applied by the code official and the engineer or architect of record.
Occupant load. Building codes assign floor area per occupant by use. Washington’s state building code (WAC 51-50-1004, effective March 16, 2024) lists exercise rooms at 50 gross square feet per occupant. Illustratively, under that factor each additional 1,000 gross square feet of exercise room adds 20 occupants to the calculated load. Your adopted code and the code official’s classification decide the factor that applies.
Plumbing fixtures. The International Plumbing Code is a model code published by the International Code Council; its Table 403.1 sets minimum fixture counts by occupancy, and jurisdictions adopt it with amendments or use a different plumbing code. Michigan’s rules adopt the 2021 IPC (R 408.30701) and amend Table 403.1 (R 408.30758, effective March 12, 2024). The A-3 row of Michigan’s amended Table 403.1, which includes gymnasiums, requires 1 water closet per 125 male and 1 per 65 female occupants; occupants are determined under the Michigan building code, and the total is divided in half to find the load for each sex. Whether a fitness space falls in that row is the code official’s call. HFA’s article on locker room size says there are no specific industry standards for locker room size and that fixture requirements depend on the local plumbing code, occupancy load and jurisdiction.
Accessibility. Under the ADA Standards (section 202.4), an alteration that affects an area containing a primary function must, to the maximum extent feasible, make the path of travel to that area accessible, “including the rest rooms, telephones, and drinking fountains serving the altered area,” unless that would be disproportionate to the overall alteration in cost and scope. Expanding a training floor can therefore bring existing restrooms into the project.
Changing rooms, lockers and showers
Measure these as throughput, not fixture counts. Records to pull:
- Showers: positions available, and the queue at the busiest finishing times, especially after classes end, on several busy days.
- Lockers: occupied lockers at peak divided by the total; members carrying bags onto the floor is a visible signal.
- Toilets and lavatories: queues at peak, and the fixture count the architect calculates for the expanded occupant load under your adopted code.
- Visit length: average time between check-in and departure, from access control data. Programming that lengthens visits keeps lockers occupied longer.
Where these facilities are provided, the ADA Standards require at least one accessible shower or bathtub (section 213.3.6); at least 5 percent, and no fewer than one, of each type of locker to comply with section 811 (section 225.2.1); and at least 5 percent, and no fewer than one, of each type of locker room use in each cluster to comply with section 803 (section 222.1). An expansion that adds lockers or changing rooms adds to those counts.
Air, power, parking and supervision
Ventilation follows occupancy and use. Washington’s mechanical code (WAC 51-52-0403, effective March 16, 2024) lists a default occupant density of 10 people per 1,000 square feet for a health club weight room and 40 for an aerobics room, each with 20 cfm of outdoor air per person plus 0.06 cfm per square foot. Converting a weight area to group exercise can therefore raise the design occupancy of the same room. These ventilation densities are separate from the building code’s occupant load factor, which is the figure used for plumbing fixture counts. The mechanical engineer decides what your adopted code requires.
Power. Consoles, screens, charging and recovery units draw on circuits sized for the old floor. Get a load survey against the panel and the manufacturer’s electrical requirements for every powered unit on the order, using the schedule in cardio electrical requirements.
Parking. Count occupied spaces on several peak evenings and check the lease for allocated spaces. If the project adds parking, ADA section 208 sets the minimum number of accessible spaces; for example, 1 for a facility with 1 to 25 spaces and 2 for 26 to 50.
Supervision. Compare members present at peak, from check-in data, with staff rostered on the floor, and walk the new zone to see what is visible from where staff stand. A zone nobody can see changes the staffing plan.
| Constraint | Measure on your site | Who confirms the requirement | Signal it binds first |
|---|---|---|---|
| Floor and stations | Occupancy and waits by station at peak; walkway encroachment | Operator; manufacturer live areas | Training in walkways; waits at several stations |
| Plumbing fixtures | Queues at peak; existing fixture count | Architect or plumbing engineer, under the adopted plumbing code | Required fixtures at the new load exceed what exists |
| Showers and lockers | Shower queue after classes; lockers occupied at peak | Operator; architect for ADA scoping | Queues after class; bags on the floor |
| Ventilation | Heat and air complaints; current design occupancy | Mechanical engineer, under the adopted mechanical code | A change of use raises design occupancy |
| Electrical | Load survey against the panel; unit requirements | Electrician; manufacturer electrical sheets | Trips under load; no spare circuits |
| Accessibility | Route to the new area; restrooms serving it | Architect; code official | Restrooms on the path of travel are not accessible |
| Parking | Occupied spaces on peak evenings; lease allocation | Landlord; local zoning; ADA section 208 if spaces are added | Members circling or parking off-site |
| Supervision | Members present per staff member at peak; sightlines | Operator | New zone not visible from staffed positions |
Size the order for the first constraint to bind
Model the expanded scenario on every line, not only the floor: apply your own projection of members at peak and visit length to each measurement, and get the code calculations at the new scope. Then name the constraint that binds first and write it at the top of the specification. If changing rooms bind, the project includes changing-room work or the equipment order is trimmed to what they support. If floor area binds, denser or multi-purpose stations may do more than additional units. If supervision binds, part of the budget belongs in staffing rather than steel. Each is a legitimate outcome.
Triggers you set: the headroom on each line, in its own unit, below which relief must be funded inside the same project; and a re-measure date after opening.
Red flags:
- An order sized from a station queue count alone.
- No fixture or ventilation calculation at the new occupant load.
- Code values from another jurisdiction used as if they were national.
- A lease that does not say who pays for code-required building work; see checking the lease and building before ordering.
Delivery and installation sequencing then follow the settled scope, as in the installation readiness plan.
What to do this week
- Measure each constraint at peak, in its own unit, on several busy days.
- Ask the architect for occupant load, plumbing fixture and ventilation calculations for the expanded scope, under the code editions in force when you apply for permits.
- Check ADA scoping for showers, lockers and locker rooms, and the restrooms on the path of travel to the altered area.
- Get a panel load survey and the electrical sheets for every powered unit on the order.
- Name the binding constraint at the top of the specification and resize the equipment order to it.
Continue with FEX
- Five evidence checks before committing capital
- Building an equipment cash-flow case
- Planning accessible clear floor space and routes
FEX editorial guidance: the constraint check and sizing method are FEX analysis. Code values cited are examples from Michigan and Washington as adopted on the dates shown, not national requirements. Michigan has proposed adopting the 2024 IPC and Washington’s 2024 codes are scheduled to take effect May 3, 2027, so confirm the edition in force when you apply for permits. The code adopted in your jurisdiction, the code official and the engineer or architect of record decide what applies. This is not legal, engineering or code advice.
Source notes
- Michigan Admin. Code R 408.30758, Minimum number of fixtures (via Cornell LII; amended effective March 12, 2024) — Amended Table 403.1 A-3 row; occupant determination.
- Michigan Admin. Code R 408.30701 (via Cornell LII; effective March 12, 2024) — Adoption of the 2021 International Plumbing Code.
- Washington State Legislature: WAC 51-50-1004, Occupant load (effective March 16, 2024) — Exercise rooms at 50 gross square feet per occupant.
- Washington State Legislature: WAC 51-52-0403, Mechanical ventilation (effective March 16, 2024) — Health club ventilation rates and default densities.
- Michigan LARA Bureau of Construction Codes: Currently Open Rules (accessed October 9, 2026) — Proposed Part 7 rules adopting the 2024 IPC.
- Washington State Building Code Council (accessed October 9, 2026) — 2024 codes effective May 3, 2027.
- U.S. Access Board: ADA Accessibility Standards (accessed October 8, 2026) — Sections 202.4, 208 and 213.3.6.
- eCFR: 36 CFR part 1191, appendix B, ADA scoping (accessed October 8, 2026) — Sections 222.1 and 225.2.1.
- Health & Fitness Association: Everything You Need to Know About Health Club Locker Room Size (June 23, 2016) — No industry standard; fixtures depend on local code.
Editorial update, October 9, 2026: Removed the month-by-month narrative, the 15 percent headroom threshold and other unsourced claims, and reframed the piece as a constraint check built on the operator’s own peak counts. Added verified plumbing, occupant load and ventilation examples from Michigan and Washington, the ADA requirements for showers, lockers, locker rooms, parking and path of travel, and removed a shared stock photo.
