How Plumbing Subs Bid and Bill Commercial Work

By Wyatt Cooper · Published October 14, 2026 · 6 min read

Key takeaways

Commercial plumbing follows three inspected phases, underground, rough-in and finish, and the schedule of values should follow them too.
Clarify the edges in the bid: where site utilities stop, excavation and backfill, owner-furnished fixtures, gas, and fire protection.
Fixtures are a large material purchase, so a separate fixture material line lets you bill them as stored when they are delivered, where the contract allows.
In the example below, finishing underground in month 2 bills $31,380, with $3,138.00 retained at 10% and $28,242.00 due.

Plumbing subcontractors bid commercial work from a takeoff of fixtures, pipe by system and size, equipment such as water heaters, and the labor for each phase, with clarifications for site utilities, excavation, gas, owner-furnished fixtures and fire protection. They bill monthly against a schedule of values split by phase: underground below the slab, rough-in or top-out of waste, vent and water, and finish when fixtures are set and trimmed, plus equipment, testing and closeout lines.

The three phases of commercial plumbing

1UndergroundSanitary and storm piping below the slab, tested and inspected before backfill and the slab pour
2Rough-in (top-out)Waste, vent and domestic water piping in walls and ceilings, tested and inspected before walls close
3FinishFixtures set and trimmed, equipment connected, systems started and flushed, final inspection

The plumbing phases on a slab-on-grade commercial building, each usually inspected before it is covered

The phases are set by the work itself and by the inspections the local plumbing code requires before each is covered, so your billing and your crew plan should follow them. The trade's associations, the Plumbing-Heating-Cooling Contractors Association (PHCC) and the Plumbing Contractors of America, part of the Mechanical Contractors Association of America (MCAA), publish education and resources for contractors in this work.

Clarifications that protect a plumbing bid

Plumbing scope edges to state in every commercial bid
Item	The question	State in the bid
Site utilities	Where does your work start: at the building wall, a set distance out, or at the main?	The point of connection for sewer, storm and water
Excavation and backfill	Who digs, shores, backfills and compacts the underground?	Included, or by the site contractor
Slab work	Who saw-cuts, cores and patches?	Included or by others, and whether firestopping is yours
Fixtures	Contractor-furnished, or owner-furnished and you install?	Which fixtures you furnish and which you only set
Gas piping	In the plumbing scope or the mechanical scope?	Included from meter to equipment, or excluded
Fire protection	Sprinklers are often a separate trade	Excluded unless the bid says otherwise
Permits and fees	Who pulls the permit and pays utility tap fees?	Permit included; tap and impact fees by owner, or as priced

Ask unclear items through the GC's bid questions so every bidder hears the answer. A GC reading your exclusions will price any gap against you when it levels the bids.

A schedule of values that follows the phases

A fictional $284,000 plumbing schedule of values, grouped by phase
Line	Description	Phase	Scheduled value
1	Mobilization and submittals	General	$8,500
2	Underground sanitary and storm	Underground	$52,300
3	Rough-in, waste and vent	Rough-in	$61,800
4	Rough-in, domestic water	Rough-in	$47,600
5	Gas piping	Rough-in	$18,900
6	Fixtures, material	Finish	$39,400
7	Fixtures, set and trim	Finish	$22,700
8	Water heaters and equipment	Finish	$21,300
9	Testing, inspections and startup	General	$6,000
10	Closeout documents	General	$5,500
	Total		$284,000

By phase: underground $52,300; rough-in $61,800 + $47,600 + $18,900 = $128,300; finish $39,400 + $22,700 + $21,300 = $83,400; general $8,500 + $6,000 + $5,500 = $20,000. The four add to $284,000. Rough-in is the largest phase, which is why a sub that splits it by system or by floor can bill steadily through the middle of the job.

Worked example: billing the underground

The fictional "Ostrander Plumbing" holds the subcontract above with 10% retainage. At the end of month 1 the underground was 40% complete ($20,920 billed). In month 2 it is finished, tested and inspected, and the slab is poured.

Ostrander Plumbing, pay app 2, line 2: underground sanitary and storm

Scheduled value: $52,300.00
Previous (40%): $20,920.00
This period (60%): $31,380.00
Completed to date (100%): $52,300.00
Retainage on this period at 10%: $3,138.00
This line's share of the payment due: $28,242.00

Month 2 billing on line 2 (fictional)

Checks: 40% of $52,300 is $20,920; 60% is $31,380; together $52,300. 10% of $31,380 is $3,138.00, and $31,380 − $3,138 = $28,242. Bill the inspection-passed phase when it passes; a GC will often ask for the inspection record before it approves a line at 100%.

Stored fixtures and equipment

Fixtures and water heaters often arrive weeks before they are set. Whether you can bill them as stored material depends on the contract. On federal fixed-price work, material delivered to the site may be counted, and material stored elsewhere only where the contract specifically authorizes it and you show you have title (FAR 52.232-5). Private subcontracts usually want a bill of sale, insurance and secure storage. Retainage applies to stored material too; see how to calculate retainage.

Plumbing closeout documents

As-built drawings showing underground and concealed piping as installed.
Test records and inspection sign-offs for each phase.
Backflow preventer test reports and water system disinfection reports where the jurisdiction or specification requires them.
O&M manuals and warranties for water heaters, pumps and fixtures.
The final lien waiver and the retainage release request.

For the monthly form itself, see how to fill out a pay application as a subcontractor.

How it works in Conflo

When a GC sends a plumbing package through Trade bids in Conflo, the sub prices the GC's scope items, marking each included or excluded, prices alternates and lists exclusions and qualifications, and can revise the bid until the due time. If it wins and signs the subcontract, it bills in Pay apps: percent complete this period and materials stored for each line, with previous billing carried forward and retainage calculated on completed and stored to date. The GC can send back single lines with a note.

The same pay app as the electrical subcontractor sees it in Conflo: waiting on the GC, the payment steps, what is holding payment, the application summary and the schedule of values with this period, stored and to-date amounts. — A sub's pay app in Conflo: this period, stored and to-date amounts on each schedule-of-values line, and what is holding payment.

Not built today: attaching an inspection record to a schedule-of-values line.

The bottom line

Plumbing bids and bills follow the same three phases the inspector does. Clarify where your work starts and stops, split rough-in so it can be billed as it goes, and keep fixtures on their own material line.

Before the next bid, check your proposal template against the seven clarifications above.

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Sources

Plumbing-Heating-Cooling Contractors Association — PHCC. Read October 16, 2026.
Who We Are — Mechanical Contractors Association of America. Read October 16, 2026.
FAR 52.232-5, Payments under Fixed-Price Construction Contracts — Acquisition.gov, U.S. General Services Administration. Read October 16, 2026.

Questions

What are the phases of commercial plumbing?

Underground below the slab, rough-in (also called top-out) of waste, vent and water piping in walls and ceilings, and finish, when fixtures are set and trimmed and equipment is connected. Each is usually inspected before it is covered.

How should a plumbing sub split its schedule of values?

By phase and system: underground, rough-in split by system or floor, gas, fixture material, fixture setting, equipment, testing and closeout. That lets each phase bill as it is completed and inspected.

What should a plumbing bid exclude or clarify?

The point of connection to site utilities, excavation and backfill, saw-cutting and coring, owner-furnished fixtures, gas piping, fire protection, and permit and tap fees.

Can a plumbing sub bill for fixtures before they are installed?

Often, as stored material, if the contract allows it and you provide what it asks for, such as a bill of sale, insurance and secure storage. Retainage usually applies.