Plumbing Scope of Work: What GCs Need to Include (and What Gets Missed)

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.

Domestic Water Systems

• Water service entry: Confirm the connection point, meter size, and pressure-reducing valve (PRV) setting. 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 — 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. Do not leave material selection to the sub's discretion.
• Recirculation system: Hot water recirculation loop with in-line circulating pump. Specify minimum return temperature at the most remote fixture (typically 50°C/122°F to prevent Legionella growth). This is omitted more often than it's included.
• Pressure testing: Minimum 1.5× maximum operating pressure or 860 kPa, whichever is greater. 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. 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 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 (CAN/CSA-B70 or ASTM A74) with neoprene compression gaskets for buried runs; copper DWV or cast iron above grade. No-hub couplings 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. 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 above roof level and minimum 3m horizontal from any air intake. Coordinate vent termination locations with roofing membrane penetrations.

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 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. Specify compaction requirement (typically 95% Standard Proctor) under slabs.
• Shoring and dewatering: Sub is responsible for all shoring, sheeting, and dewatering as required by local OH&S regulations. 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 compliance requirements, carrier system requirements for wall-hung water closets, 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 CSA-B64 category (RP type for high-hazard connections; DCVA for low-hazard). Specify who performs the mandatory annual certification test.
• Water hammer arrestors: Required on all branch supplies to flush-valve fixtures. 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. 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.

These are items required to complete the plumbing scope that are regularly omitted from sub bids, creating disputes or unexpected GC costs during construction.

• 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 applicable energy code. This is commonly excluded from plumbing bids and priced separately — confirm.
• Firestopping: ULC-listed firestopping at all plumbing penetrations through fire-rated walls and floor assemblies. 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 National Building Code or IBC. On post-disaster facilities, seismic design must be by P.Eng. 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.

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.
• 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. Floor drain locations for all sprinkler test and drain assemblies must be confirmed before plumbing rough-in.