Plumbing Scope of Work: Water Service, DWV, Fixtures, and Underslab Excavation
How to write a commercial plumbing scope — water service entrance, DWV per IPC/UPC, hot water recirc, backflow preventers, fixture schedules, and underslab trenching.
A well-written plumbing scope of work protects the GC on both sides — it holds the sub accountable for the complete system while preventing scope creep on work that was never part of the deal. Whether you're issuing a subcontract for a commercial office, institutional building, or multi-residential project, the gaps in plumbing scopes are predictable. This guide covers what to include in a plumbing scope of work, organized by the three areas where most gaps occur: the trade-specific work itself, the package items subs routinely omit, and the coordination requirements that fall between trades.
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Domestic Water, Sanitary, Underslab Excavation, and Fixtures
What a plumbing scope must define — water service entrance and PRV, DWV piping per IPC/UPC, underslab trenching and bedding, fixture schedules by model, and the specialty items (backflow, water hammer, trap primers) that are routinely missed.
Domestic Water Systems
Water service entry: Confirm the connection point, meter size, and pressure-reducing valve (PRV) setting per the local water utility's pressure. Specify whether the sub is responsible from the property line or from an existing stub-out. Ambiguity here is a source of claims.
Hot and cold water distribution: Specify pipe material by zone per IPC Chapter 6 or UPC Chapter 6 — copper Type L hard-drawn above grade; copper Type K soft-annealed for buried runs with no buried joints. If PEX is acceptable in commercial applications, call it out (and reference the manifold layout). Do not leave material selection to the sub's discretion.
Recirculation system: Hot water recirculation loop with in-line circulating pump per ASHRAE 90.1. Specify minimum return temperature at the most remote fixture (typically 50°C / 122°F to prevent Legionella growth per ASHRAE 188). This is omitted more often than it's included.
Pressure testing: Minimum 1.5× maximum operating pressure or 125 psi (860 kPa), whichever is greater, per IPC 312.5. Test before walls are enclosed. Require GC notification 24 hours prior to testing.
Chlorination and flushing: Full system flush (minimum 8 hours) and chlorination of the domestic water system prior to occupancy per AWWA C651. Bacteriological testing and passing results required.
Sanitary, Waste, and Vent
Scope boundary — who carries what: The plumbing sub's sanitary scope must start at a clearly defined point. Typically: from 5 ft (1.5m) outside the building to the furthest interior fixture. Confirm in writing whether the exterior site connection (from city main to building) is civil or plumbing scope.
Piping material by location: Cast iron soil pipe (ASTM A74 in US; CAN/CSA-B70 in Canada) with neoprene compression gaskets for buried runs; copper DWV or cast iron above grade. No-hub couplings (CISPI 310) required for all horizontal buried joints.
Invert elevations: Require the sub to field-verify all invert elevations before rough-in begins. Slab thickness variations, grade beams, and existing utility conflicts are the most common causes of rework. Do not allow the sub to assume design elevations without field verification.
Clean-out locations: At all direction changes greater than 45°, at the base of all stacks, and at the building perimeter per IPC 708. Cover type must match floor finish — nickel bronze in tile, round stainless in polished concrete, carpet access covers where applicable.
Vent termination: All vents terminate minimum 1m (3 ft) above roof level and minimum 3m (10 ft) horizontal from any air intake per IPC 904. Coordinate vent termination locations with roofing membrane penetrations and any nearby HVAC outside air intakes.
Excavation and Trenching for Underground Plumbing
Tip: This is the most commonly omitted item in commercial plumbing scopes. If it's not explicitly stated, assume it's excluded from the sub's price.
Scope boundary: The plumbing sub carries all excavation, trenching, bedding, and backfill for underslab and below-grade sanitary, storm, and domestic water piping within the building footprint. Confirm in writing who carries exterior site trenching — this is typically the civil or site contractor.
Trench preparation and bedding: Minimum 150mm (6 in) granular bedding (clear stone or granular A) below pipe centreline. Pipe zone backfill in 150mm compacted lifts with material free of rocks greater than 50mm (2 in). Specify compaction requirement (typically 95% Standard Proctor) under slabs.
Shoring and dewatering: Sub is responsible for all shoring, sheeting, and dewatering as required by OSHA 1926 Subpart P (or provincial OH&S in Canada). This must be explicitly in scope — it is often left out, and the GC ends up carrying the cost.
Testing before backfill: Pressure test all buried systems before allowing backfill. GC must inspect and sign off. Never permit backfill of untested piping — this single requirement prevents the most expensive plumbing rework on any project.
Cast-in sleeves: Require sleeves for all penetrations through foundation walls and grade slabs set before concrete is poured. Missed sleeves mean core drilling — at substantial cost and schedule impact. Best GCs require a sleeve coordination drawing approved before any slab pours.
Fixtures and Equipment
Fixture schedule: Every fixture specified by manufacturer and model number, not just type. Include flush valve type (sensor/battery-powered vs. hardwired manual), ADA / barrier-free compliance per ICC A117.1, carrier system requirements for wall-hung water closets (Smith, J.R. Smith, Zurn, Watts), and grab bar backing locations.
Water heaters: Specify capacity (litres or gallons), energy source, first-hour recovery rate, and all trim: ASME T&P relief valve, expansion tank, thermometer, drain valve, isolation valves. Factory start-up by manufacturer's representative required for commercial units.
Drain schedule: Provide a complete schedule covering all floor drains (FD), hub drains (HD), roof drains (RD), and trench drains (TD). Specify body material, strainer material, and cover type to match floor finish in each area.
Specialty Systems
Backflow prevention: Identify each device by application — RP (reduced pressure principle) for high-hazard cross-connections; DCVA for low-hazard, per AWWA M14 and CSA-B64 in Canada. Specify who performs the mandatory annual certification test.
Water hammer arrestors: Required on all branch supplies to flush-valve and quick-closing valve fixtures per IPC 604.9. Specify PDI-WH201 rating by fixture unit count. Omitting these causes noise complaints and premature valve failures.
Trap seal primers: Required for all floor drains not in daily use per IPC 1002.4. Pressure-drop type or electronic manifold (120V). Without primer, floor drain traps dry out and allow sewer gas into occupied spaces — a code violation and an occupant complaint.
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Common Plumbing Scope Gaps at Buy-Out
Items required to complete plumbing that are regularly excluded from sub bids — pipe insulation, firestopping, seismic restraints, hoisting, access doors — creating disputes or unexpected GC costs once construction is underway.
Permits and inspections: Plumbing sub obtains and pays for all required plumbing permits and arranges all rough-in and final inspections. Include cost of any re-inspections. Never assume permits are in scope without stating it.
Pipe insulation: Thermal insulation on all domestic hot water supply, recirculation, cold water supply in unconditioned zones, and all roof drain leaders. Specify thickness by pipe size per ASHRAE 90.1 Table 6.8.3 or IECC. This is commonly excluded from plumbing bids and priced separately — confirm.
Firestopping: UL-listed firestopping at all plumbing penetrations through fire-rated walls and floor assemblies per UL 1479 / ASTM E814. Confirm whether this is in the plumbing sub's scope or carried by a dedicated firestopping sub.
Seismic restraints: Required for all piping, water heaters, and pumps per IBC and ASCE 7 (or National Building Code in Canada). On post-disaster facilities, seismic design must be by P.Eng. or licensed structural engineer. Often bid as a lump allowance — require a fixed price.
Access doors: Supply of access panels for all concealed cleanouts, isolation valves, and equipment requiring service access. Installation is typically by drywall or millwork — confirm the split and ensure access door locations are coordinated on reflected ceiling plans.
Housekeeping pads: Layout and coordination of concrete equipment pads for domestic water heaters, booster pumps, and sump pumps. Anchor bolts cast in. Confirm who does the concrete work — typically the GC, but the plumbing sub must provide the layout.
Hoisting and rigging: Moving large water heaters or duplex sump pump assemblies into confined mechanical rooms frequently requires a forklift or chain hoist. This is often not included in base bids.
Temporary water: If the GC requires the plumbing sub to provide temporary water service during construction, it must be an explicit scope item. It is not automatic.
Waste disposal: Legal removal and disposal of all excavation spoil and construction debris generated by plumbing work.
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Plumbing Coordination with Mechanical, Electrical, Structural, and Fire Protection
Plumbing touches more trades than almost any other scope — the interface items that define who carries condensate routing, sump pump power, fixture backing, and fire-system water-service tie-ins.
Plumbing touches more trades than almost any other scope on a project. These coordination items define the interface — and prevent the finger-pointing that happens when they're left undefined.
Electrical: Power for domestic water heaters (confirm voltage, phase, and ampacity), recirculation pumps, sump pumps, and electronic trap primer manifolds (120V). Battery-powered sensor fixtures — confirm whether hardwired backup connection is required.
Concrete/civil: Invert elevations for site sewer and water connections, sump pit dimensions and locations, underslab aggregate depth for radon systems, and sleeve locations for all foundation wall and slab penetrations. Require a sleeve shop drawing approved by GC before any concrete pours.
Structural: Hanger inserts for above-grade sanitary piping. Wall backing and carrier framing for wall-hung water closets and lavatories — these must be in the structural or framing sub's scope with dimensions provided by the plumbing sub.
Architectural/GC: Chase widths and depths for wall-hung fixture carriers. Countertop cut-out dimensions for sink fixtures. Finish floor schedule is required to order the correct floor drain cover — do not proceed without it.
HVAC/mechanical: Condensate drain connection points from all HVAC equipment (chillers, ERVs, fan coil units) to the nearest floor drain provided by the plumbing trade. Confirm drain locations before mechanical equipment is set. Make-up water connections to hydronic systems and humidifiers — confirm responsibility for the connection point.
Controls: BMS monitoring points for sump pump high-water alarms, domestic hot water supply and return temperatures, and master mixing valve status.
Fire protection: Coordinate incoming water service connection for fire suppression with the fire protection sub — typically a shared service entrance with a backflow preventer specific to the fire main. Floor drain locations for all sprinkler test and drain assemblies must be confirmed before plumbing rough-in.
Plumbing Scope of Work — FAQ
What is a plumbing scope of work?
A plumbing scope of work is the contract document defining what the plumbing sub will furnish and install — typically domestic water (hot and cold supply, recirculation, water heaters), sanitary waste and vent piping, storm drainage, fixtures, and specialty systems (backflow, water hammer arrestors, trap primers). It also defines the boundary (where the sub's work starts and stops at the building line), the underslab excavation responsibility, and the interfaces with mechanical, electrical, structural, and fire protection trades. A good plumbing SOW references the applicable code (IPC, UPC, or CPC) and the AHJ.
Where does the plumbing sub's scope start and stop at the building line?
State it explicitly. Common convention: the plumbing sub picks up domestic water at the meter (or 5 ft outside the building if there's a remote meter), sanitary at the building line (5 ft / 1.5m outside the foundation), and storm at the roof drains down to the building line. The civil or site sub carries the runs from the city main into the building line. Ambiguity at this boundary is the #1 source of plumbing change orders — write it into the SOW with a specific distance from the foundation.
Is underslab excavation in the plumbing sub's scope?
By default it should be — and by default it's the most commonly excluded line item. Within the building footprint, the plumbing sub carries trenching, bedding (150mm granular below pipe), pipe-zone backfill, and compaction to 95% Standard Proctor under slabs. Outside the building footprint it's typically civil or site. State this explicitly in the SOW. Also state who carries shoring and dewatering per OSHA 1926 Subpart P — these are non-trivial costs that often get carried by the GC because they were silently excluded.
What backflow preventers do I need to specify?
By application, per AWWA M14 (or CSA B64 in Canada): RP (reduced pressure principle) for high-hazard cross-connections — boiler feed, irrigation with chemical injection, fire suppression. DCVA (double check valve assembly) for low-hazard — fire mains without chemical, domestic supply to mixed-use systems. Atmospheric vacuum breakers for hose bibbs and laboratory faucets. State each application in the fixture schedule and require annual certification by a licensed cross-connection control specialist as a closeout deliverable.
How do you handle hot water recirculation and Legionella prevention?
Spec a continuous recirculation loop with minimum return temperature of 50°C (122°F) at the most remote fixture, per ASHRAE 188 control measures. The pump runs continuously or on a time clock with temperature monitoring at the return. Mixing valves at point of use reduce delivered temperature to 43°C / 110°F for ADA fixtures. State sensor locations and BMS monitoring points so the building operator can verify return temperatures. Recirc is one of the most-omitted items on plumbing bids — and a real Legionella liability if missed on healthcare or long-term care projects.
Who provides the carrier and wall backing for wall-hung fixtures?
Plumbing sub furnishes the carrier (Smith, J.R. Smith, Zurn, Watts), with model and rough-in dimensions on the fixture schedule. The framing or structural sub provides wall backing per the plumbing sub's dimensions. State this split in both subcontracts so the GC isn't field-mediating dimensions between the plumber and the drywaller. Grab bar backing for ADA-compliant restrooms must be in the framing scope with locations from the fixture schedule.
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