2.4 Minimum Fixture Counts in Washington: IBC Table 2902.1, Not UPC Table 422.1
Key Takeaways
Washington's WAC 51-56 amendment states that UPC Sections 422.1 through 422.5 and Table 422.1 are not adopted; minimum fixtures come from Building Code Chapter 29 and Table 2902.1.
Washington also does not adopt UPC 415.2, drinking fountain alternatives, and refers to Building Code Chapter 29 instead.
Under the IBC method, the occupant load is split half male and half female, and fractional fixture results are rounded up to the next whole number.
IBC Table 2902.1 requires business occupancies to provide water closets at 1 per 25 for the first 50 and 1 per 50 for the remainder, per sex.
IBC Table 2902.1 requires restaurants to provide 1 water closet per 75 per sex, 1 lavatory per 200, and 1 drinking fountain per 500.
The Washington Rule
In most UPC states, the minimum number of water closets, lavatories, and drinking fountains comes from UPC Table 422.1. Washington is different. The state amends UPC 422.0 as follows:
422.0 Minimum Number of Required Fixtures. For minimum number of plumbing fixtures required, see Building Code chapter 29 and Table 2902.1. Sections 422.1 through 422.5 and Table 422.1 are not adopted.
The same amendment pattern applies to drinking fountains:
415.2 Drinking Fountain Alternatives. This section is not adopted. See Building Code chapter 29.
For the exam, the high-yield fact is where the numbers come from: the International Building Code (IBC) as adopted in Washington, not the UPC. A question that asks for "UPC Table 422.1" ratios in a Washington context is testing whether you know the table is not adopted. The UPC still governs how each required fixture is installed (Chapter 4), connected to drainage (Chapter 7), vented (Chapter 9), and supplied (Chapter 6).
Who Uses Fixture Counts
Designers and plan reviewers normally set fixture counts. Journey level plumbers still need to recognize a noncompliant layout, especially on tenant improvements, where a change of use can raise the required count. Fixture counts also feed directly into the drainage and water sizing you will do on Parts 2 and 3 of the exam. Every added water closet adds drainage fixture units and water supply fixture units.
The IBC Calculation Method
- Occupancy and occupant load: Use the occupant load and occupancy classification from the building code, usually shown on the architectural plans.
- Split by sex: Divide the total occupant load in half to get the male and female loads.
- Apply the ratios: Apply each fixture ratio in Table 2902.1 to each half.
- Round up: Round any fractional result up to the next whole number. In a mixed occupancy, sum the fractions for each occupancy first, then round up.
- Table footnote a: Each ratio means one fixture for the stated number of persons or any fraction of it.
Selected Rows of IBC Table 2902.1
| Occupancy | Water closets | Lavatories | Drinking fountains | Other |
|---|---|---|---|---|
| Business (offices, banks, similar uses) | 1 per 25 for the first 50 and 1 per 50 for the remainder over 50 | 1 per 40 for the first 80 and 1 per 80 for the remainder over 80 | 1 per 100 | 1 service sink |
| Educational | 1 per 50 | 1 per 50 | 1 per 100 | 1 service sink |
| Assembly: restaurants, banquet halls, food courts | 1 per 75 male; 1 per 75 female | 1 per 200 | 1 per 500 | 1 service sink |
| Mercantile (retail stores, markets) | 1 per 500 | 1 per 750 | 1 per 1,000 | 1 service sink |
| Factory and industrial | 1 per 100 | 1 per 100 | 1 per 400 | 1 service sink |
| Storage (low and moderate hazard) | 1 per 100 | 1 per 100 | 1 per 1,000 | 1 service sink |
Another table footnote says business and mercantile occupancies with an occupant load of 30 or fewer do not need a service sink.
Scope note: Always use the edition of the IBC adopted in Washington, along with any Washington amendments to Chapter 29. The rows above are the published IBC values used to illustrate the method.
Worked Example 1: Office Building (Business)
An office tenant space has an occupant load of 200.
- Split: 100 male, 100 female.
- Water closets per sex: The first 50 at 1 per 25 gives 2. The remaining 50 at 1 per 50 gives 1. Total: 3 water closets per sex.
- Lavatories per sex: The first 80 at 1 per 40 gives 2. The remaining 20 at 1 per 80 gives 0.25, which rounds up. Total: 3 lavatories per sex.
- Drinking fountains: 200 ÷ 100 = 2.
- Service sink: 1.
Worked Example 2: Restaurant
A restaurant has an occupant load of 300.
- Split: 150 male, 150 female.
- Water closets per sex: 150 ÷ 75 = 2.
- Lavatories per sex: 150 ÷ 200 = 0.75, which rounds up to 1.
- Drinking fountains: 300 ÷ 500 = 0.6, which rounds up to 1 before any building-code exceptions are applied.
- Service sink: 1.
Related Washington Chapter 4 Amendments
These amendments often travel with fixture-count questions:
| Section | Washington rule |
|---|---|
| 402.5 | Water closet and bidet front clearance 24 inches; 21 inches in dwelling and sleeping units (Section 2.1) |
| 405.4 | No fixture or fitting may be sold, installed, or approved in Washington unless it meets Chapter 4 standards |
| 407.2 | Lavatory and kitchen faucets 2.5 gpm; public lavatories 0.5 gpm (2015 amendment) |
| 407.4 | Self-closing metering faucets on lavatories in general-public restrooms |
| 408.6 | Shower compartment 900 square inches plus a 30-inch circle (Section 2.2) |
| 411.2 and 412.1 | Water closets 1.6 gpf and urinals 1.0 gpf under the 2015 amendments; no continuous-flow fixtures |
| 414.3 | Domestic dishwashers discharge through an air gap fitting; commercial dishwashers through an air gap |
| 418.3 | Floor drains in toilet rooms with two or more water closets or a water closet plus a urinal, and in commercial laundry rooms (Section 2.3) |
Exam trap: "Water bottle filling stations may replace up to 50% of drinking fountains" is the unamended UPC 415.2 text. Washington does not adopt 415.2. Drinking fountain alternatives come from Building Code Chapter 29.
A Washington plan reviewer needs the minimum number of water closets for a new retail store. Which document governs?
UPC Table 422.1 as published by IAPMO
Building Code Chapter 29 and IBC Table 2902.1, because Washington does not adopt UPC 422.1 through 422.5 or Table 422.1
The L&I plumber certification rules in WAC 296-400A
The water purveyor's cross-connection program
A business occupancy has an occupant load of 200. Using IBC Table 2902.1 (1 per 25 for the first 50 and 1 per 50 for the remainder), how many water closets are required for each sex?
8
2
3
4
Which statement about drinking fountain alternatives is correct under the 2015 UPC as amended in Washington?
Drinking fountains may be installed in toilet rooms if they are self-closing
Drinking fountains must discharge through an air gap
Bottle filling stations may replace up to 50 percent of drinking fountains under UPC 415.2
UPC 415.2 is not adopted; drinking fountain requirements and alternatives come from Building Code Chapter 29
Sections you finish are checked off in the contents.