Project Context
This walkthrough uses a representative new K-12 campus: 1,200 students and about 185,000 SF in the Dallas-Fort Worth area, owned by a public school district.
Schools concentrate a large number of fixtures in a few places (student restrooms, locker rooms, the kitchen, science labs), and those fixtures are governed by minimum-count rules, accessibility standards and food-establishment rules. A plumbing estimate for a school is mostly a fixture-and-rough-in exercise, checked against code.
What the Estimate Needs to Answer
- Do the fixture counts on the drawings meet the plumbing code minimums for the design occupant load?
- Which accessibility requirements change rough-in locations, fixture selection or trim?
- Is the grease interceptor sized for the kitchen fixtures that drain to it?
- Which wage rates apply to a public school project in Texas?
Typical Challenges
1. Minimum Fixture Counts
IPC Section 403 (Table 403.1) sets minimum plumbing fixtures by occupancy. For an Educational (Group E) occupancy, the table requires one water closet per 50, one lavatory per 50, one drinking fountain per 100 and one service sink. For an example design occupant load of 1,200 students:
| Fixture | IPC ratio (Group E) | Minimum for 1,200 occupants |
|---|---|---|
| Water closets | 1 per 50 | 24 |
| Lavatories | 1 per 50 | 24 |
| Drinking fountains | 1 per 100 | 12 |
| Service sinks | 1 | 1 |
Real projects are more involved: occupant load comes from the building code rather than enrollment, staff and assembly spaces (the gym and cafeteria) may be calculated separately, fixtures are split between sexes, and the local amendments can change the ratios. The estimating step is to run the numbers and compare them with the fixture schedule. Where the drawings show fewer fixtures than the calculation, the gap goes to the design team as a pre-bid RFI.
In the kitchen, handwashing sinks and other fixtures are also governed by the Texas Food Establishment Rules (25 TAC Chapter 228), which the health department enforces separately from the plumbing code.
2. Accessibility Items That Affect Plumbing Cost
Accessible fixtures under the 2010 ADA Standards and ICC A117.1 have plumbing consequences beyond grab bars:
- Water closet location and height: the centerline must be 16 to 18 inches from the side wall and the seat 17 to 19 inches high, which affects the waste rough-in location and fixture selection.
- Lavatory pipe protection: exposed water supply and drain piping under accessible lavatories must be insulated or otherwise protected, so under-lavatory guards or insulation kits are counted for every accessible lavatory.
- Drinking fountains: accessibility rules generally require both a wheelchair-accessible unit and a standing-height unit, so a single-height fountain in the schedule may need to be a bi-level unit.
- Carriers: wall-hung fixtures common in schools need carriers, which are often listed only in the specifications.
3. Grease Interceptor Sizing
A school kitchen that discharges fats, oils and grease to the public sewer generally needs a grease interceptor. Many jurisdictions require a gravity interceptor sized by the local utility’s rules; where a hydromechanical interceptor is allowed, the PDI G101 method is commonly used to size it from the fixtures it serves.
Example (PDI G101 drainage method): a three-compartment pot sink with compartments 24 in x 24 in x 14 in deep.
- Volume of one compartment: 24 x 24 x 14 = 8,064 cubic inches / 231 = 34.9 gallons
- Three compartments: 34.9 x 3 = 104.7 gallons
- Fill factor of 75%: 104.7 x 0.75 = 78.5 gallons of drainage load
- Flow rate at a 2-minute drainage period: 78.5 / 2 = 39.3 GPM (at a 1-minute period it would be 78.5 GPM)
- Select the next standard interceptor size at or above the design flow, for example a 50 GPM unit for the 2-minute case
Add other fixtures that drain through the interceptor as the local rules require. Check the kitchen equipment schedule against the plumbing drawings: when the interceptor on the drawings is smaller than the fixtures require, that becomes an RFI rather than a change order.
4. Prevailing Wage on Texas Public Work
Texas Government Code Chapter 2258 requires public bodies, including school districts, to determine and pay prevailing wage rates on public works. Each district adopts its own wage schedule, and federally funded work may also carry Davis-Bacon rates. The estimate should use the rates in the bid documents, burdened for your own taxes and insurance, rather than a statewide open-shop average.
Applicable Codes and Standards
- International Plumbing Code (IPC), Section 403 – minimum plumbing facilities, as adopted and amended locally
- 2010 ADA Standards for Accessible Design and ICC A117.1 – accessible fixtures
- PDI G101 – testing and rating of hydromechanical grease interceptors (sizing method)
- Texas Food Establishment Rules (25 TAC Chapter 228)
- Texas Government Code Chapter 2258 – prevailing wage rates on public works
Software Workflow
| Software | Purpose |
|---|---|
| PlanSwift | Fixture counts and pipe lengths from PDF sheets |
| Bluebeam Revu | Markups, fixture-schedule cross-checks, RFI log |
| RSMeans Data Online | Reference unit costs and City Cost Index adjustments |
Common Estimating Risks
| Risk area | Why it matters | Mitigation |
|---|---|---|
| Fixture counts below code minimum | Permit comments and added fixtures after award | Run the IPC calculation; RFI before bid |
| Accessibility items missed | Guards, carriers and bi-level fountains left unpriced | Check every accessible fixture against the standard |
| Interceptor undersized on drawings | Replacement or added unit during construction | Size from fixtures and local rules; RFI |
| Wrong wage basis | Labor understated on a labor-heavy trade | Use the district’s wage schedule |
Takeaways
- Code minimums are a check, not an assumption. Run the fixture calculation against the drawings.
- Accessibility is quantifiable plumbing scope. Rough-ins, guards, carriers and fountains all carry cost.
- Size the interceptor with math. The fixtures that drain to it set the flow.
How We Apply This on Real Bids
For plumbing bids, we count fixtures by room from the drawings and the fixture schedule, check them against the adopted code, and list gaps as RFIs. See our plumbing estimating services, institutional estimating, or pricing.