A plumbing estimate is mostly pipe, fittings and fixtures, but what drives the cost is detail. You have several pipe materials, each with its own joining method. You have below-grade work that depends on depth and slope. Fixtures often come with carriers and trim that are listed only in the specifications. And there are specialty systems like medical gas that need certified installers. A clean takeoff keeps each system separate and makes these drivers visible.
This guide covers how commercial plumbing estimates are commonly organized, how fixture units work under the International Plumbing Code (IPC), and how slope and hanger spacing affect quantities. It includes worked examples.
Division 22 Scope
In CSI MasterFormat, plumbing is Division 22 – Plumbing. The main sections include:
- 22 05 00 – Common Work Results for Plumbing (hangers, supports, identification, valves)
- 22 07 00 – Plumbing Insulation
- 22 10 00 – Plumbing Piping (facility water distribution, sanitary sewerage, storm drainage)
- 22 30 00 – Plumbing Equipment (water heaters, pumps, water softeners)
- 22 40 00 – Plumbing Fixtures
- 22 50 00 – Pool and Fountain Plumbing Systems
- 22 60 00 – Gas and Vacuum Systems for Laboratory and Healthcare Facilities (medical gas)
Natural gas piping inside a building is classified in Division 23 (23 11 23 Facility Natural-Gas Piping), but it is often carried by the plumbing contractor. Site utilities beyond 5 ft from the building are commonly in Division 33 – Utilities. Read the drawings and spec sections to settle who owns what.
Pipe Takeoff by System
Take off each system separately, by material and size:
- Domestic cold, hot and hot water return: copper Type K, L or M, PEX, or CPVC as specified. Include valves, balancing valves, backflow preventers, expansion tanks and insulation.
- Sanitary waste and vent: cast iron (hubless/no-hub or service weight) or PVC DWV. Separate below-grade from above-grade, because excavation, bedding and labor are very different.
- Storm drainage: roof drains, overflow drains, conductors and underground storm lines.
- Specialty systems: natural gas, grease waste with interceptors, acid waste, compressed air, and medical gas.
Count fittings by type and size (wyes, combination wye and 1/8 bends, tees, elbows, cleanouts, couplings), or use per-foot allowances that you have checked against past jobs. Fittings and joints often make up a large share of plumbing labor.
Fixture Units: DFU and WSFU
The IPC sizes drainage using drainage fixture units (DFU) from its fixture unit table. Water distribution sizing (under the IPC appendix method) uses water supply fixture units (WSFU). The estimator is not the engineer of record. Still, a quick DFU count helps confirm that pipe sizes on the drawings are reasonable and that no fixtures are missing from the riser diagrams.
Typical IPC DFU values for common commercial fixtures:
| Fixture | DFU (IPC) |
|---|---|
| Lavatory | 1 |
| Water closet, public, 1.6 gpf or less | 4 |
| Urinal, 1.0 gpf or less | 2 |
| Drinking fountain | 0.5 |
| Shower | 2 |
The Uniform Plumbing Code (UPC), used in several western states, assigns different values. Always use the tables from the code edition the jurisdiction has adopted.
WSFU values depend heavily on the flush type. A flush-valve water closet is assigned far more supply fixture units than a tank-type one, which is why buildings full of flushometers need larger mains.
Worked Example 1: DFU Count for a Restroom Group
Example (not a real project): A public restroom core contains 4 water closets (1.28 gpf flushometer), 2 urinals (0.5 gpf), 4 lavatories and 1 drinking fountain.
| Fixture | Qty | DFU each | Subtotal |
|---|---|---|---|
| Water closet (public, 1.6 gpf or less) | 4 | 4 | 16 |
| Urinal (1.0 gpf or less) | 2 | 2 | 4 |
| Lavatory | 4 | 1 | 4 |
| Drinking fountain | 1 | 0.5 | 0.5 |
| Total | 24.5 DFU |
Check: 16 + 4 + 4 + 0.5 = 24.5 DFU. Compare this load with the branch and building drain sizes on the drawings, using the IPC sizing tables. If the drawings show a line that looks undersized for the load, raise an RFI instead of repricing on your own.
Worked Example 2: Slope and Hangers
Slope and depth. The IPC’s minimum horizontal drainage slope is commonly 1/4 inch per foot for pipe 2-1/2 inches and smaller, and 1/8 inch per foot for 3 to 6 inch pipe. Example: An 85 ft run of 4” building drain at 1/8”/ft drops 85 x 0.125 = 10.625 in, or about 10-5/8 in. If the invert at the building wall is set, that fall tells you how deep the trench is at the upstream end. Trench depth drives excavation, shoring and backfill quantities.
Hanger count. Example: 120 LF of horizontal 3” PVC DWV. The IPC commonly requires horizontal support at a maximum of 4 ft for plastic pipe. 120 / 4 = 30 spaces, so about 31 hangers with one at each end. Add hangers at changes in direction and at fittings as required. By comparison, horizontal copper tubing of 1-1/2” and larger is commonly supported at 10 ft, and 1-1/4” and smaller at 6 ft. Confirm the spacing against the adopted code table and the project specifications, which may be stricter.
Fixtures and Equipment
Take off fixtures from the plumbing fixture schedule, then count them on the plans. Each fixture line should list its trim, carrier (wall-hung water closets and lavatories), supplies, stops, trap and any ADA accessories such as offset drains and insulation kits. The schedule’s flow rates (for example 1.28 gpf water closets, 0.5 gpf urinals, 0.5 gpm public lavatory faucets) should match the specifications and local water-efficiency rules.
For equipment such as water heaters, booster pumps, recirculation pumps, grease interceptors and backflow preventers, get vendor quotes. Confirm the electrical and venting requirements for each.
Medical Gas Systems
Medical gas (oxygen, medical air, vacuum, nitrous oxide, nitrogen, WAGD) is covered by NFPA 99 and is its own specialty estimate. Piping is typically Type K or L copper cleaned for oxygen service, installed with brazed joints under a nitrogen purge. Include zone valve boxes, area alarms and gas-specific outlets. Also include installer qualification, the third-party verification and certification the specification requires, and the labor for purging and pressure testing.
Plumbing Estimating Checklist
- Separate below-grade, above-grade and specialty systems
- Take off pipe by material, size and joining method
- Reconcile the fixture schedule with the plan counts and riser diagrams
- Include carriers, trim, stops and ADA accessories for each fixture
- Run a DFU check on major branches and the building drain
- Use slope to set trench depth for underground drainage
- Count hangers and supports using code or spec spacing
- Clarify natural gas and site utility scope (Divisions 23 and 33)
- Include testing, disinfection, and any required inspections or certification
- Get vendor quotes for equipment and specialty items
Common Mistakes
- Mixing below-grade and above-grade pipe into one unit price.
- Leaving out fixture carriers and trim, which are often listed only in the specifications.
- Using the wrong code tables. IPC and UPC fixture unit values differ.
- Forgetting trench depth. Slope on long underground runs adds excavation and shoring.
- Undercounting fittings on congested restroom groups.
- Treating medical gas as ordinary copper piping and leaving out certification and testing.
For related reading, see our MEP estimating guide and the material takeoff guide.
How F&K Estimatings Can Help
F&K Estimatings prepares Division 22 takeoffs by system, material and size, with fixture counts reconciled to the schedules. Unclear scope and sizing conflicts are flagged as RFIs. See our plumbing estimating services, review pricing, or contact us with your drawings.