Boston ADU Plumbing Rough-In: Complete Guide to Water, Sewer, and Gas Installation

Plumbing rough-in for Boston ADUs involves complex coordination of water supply, drainage, venting, and gas systems within the constraints of existing infrastructure and stringent local codes. This critical construction phase determines the functionality, efficiency, and code compliance of your ADU's plumbing systems. Boston's older infrastructure and strict plumbing codes require specialized knowledge and careful execution to ensure successful project completion.

Boston Plumbing Code Requirements for ADUs

Boston ADUs must comply with the Massachusetts Plumbing Code plus local amendments specific to accessory dwelling units and existing building modifications. Understanding these requirements is essential for successful rough-in planning and approval.

Water Supply System Requirements

Service Connection Options

• Separate water service: Required for ADUs over 800 sq ft in most areas
• Shared service: Acceptable with adequate pressure and flow rates
• Service upgrade: Often required when existing service inadequate
• Pressure testing: All new water supply systems require testing at 150 PSI
• Backflow prevention: Required for all ADU connections to city water

Water Supply Sizing and Materials

• Main supply line: 3/4" minimum for most ADU applications
• Branch lines: 1/2" copper or PEX for fixture supplies
• Hot water circulation: Required for runs over 50 feet
• Approved materials: Copper, CPVC, or PEX-A tubing
• Insulation: Required for all hot water lines and exterior cold water

Drainage and Venting Requirements

Sewer Connection Specifications

• Separate sewer connection: Preferred for detached ADUs
• Shared connection: Requires main line capacity verification
• Pipe sizing: 4" minimum for building drain, 3" for branches
• Materials: PVC Schedule 40, ABS, or cast iron acceptable
• Slope requirements: 1/4" per foot minimum for 4" lines

Vent System Design

• Main stack: 3" minimum diameter extending through roof
• Individual vents: 1.5" minimum for most fixtures
• Wet venting: Allowed for bathroom groups with restrictions
• Air admittance valves: Permitted with limitations in Massachusetts
• Vent termination: 12" above roof surface minimum

Fixture Planning and Layout

Bathroom Plumbing Requirements

Minimum Fixture Requirements

• Water closet: Required in every ADU
• Lavatory: Required with hot and cold water
• Bathtub or shower: Required for ADUs intended for habitation
• Floor drain: Required in bathroom areas in some jurisdictions
• Exhaust fan: Required with exterior venting

Rough-In Dimensions and Clearances

• Water closet: 12" rough-in standard, 15" minimum clearance to walls
• Lavatory: Supply lines 4" on center, 20" above floor
• Shower: Mixing valve 38-48" above floor, centered
• Bathtub: Spout 6" above rim, faucet centered on tub
• Accessibility: Consider ADA compliance for universal design

Kitchen Plumbing Design

Required Kitchen Fixtures

• Kitchen sink: Minimum one compartment with hot and cold water
• Dishwasher connection: Hot water and drain required
• Ice maker line: 1/4" copper tubing to refrigerator location
• Garbage disposal: Dedicated drain and electrical circuit
• Gas range connection: 1/2" gas line with shut-off valve

Kitchen Rough-In Specifications

• Sink supply lines: 1/2" hot and cold, 20" above floor
• Dishwasher: Hot water and drain connection under sink area
• Garbage disposal: Switch location above counter, GFCI protected
• Water filter: Pre-plumb for under-sink filtration system
• Shut-off valves: Required for all fixture connections

Water Heater Installation

Water Heater Types and Sizing

Electric Water Heaters

• Tank units: 30-50 gallon capacity typical for ADUs
• Tankless units: Sizing based on simultaneous demand
• Heat pump units: Energy efficient option for year-round use
• Electrical requirements: 240V dedicated circuit, properly sized
• Installation location: Interior preferred in Boston climate

Gas Water Heaters

• Natural gas: Connection to existing gas service
• Propane: Separate tank system for remote locations
• Venting requirements: Category I or condensing venting
• Gas line sizing: Typically 3/4" for most residential units
• Combustion air: Required for enclosed installation areas

Installation Requirements

Safety and Code Compliance

• Temperature relief valve: Required with discharge piping to floor drain
• Seismic strapping: Required in all installations
• Drain pan: Required for installations over finished areas
• Accessibility: Service access for maintenance and replacement
• Insulation: Energy efficiency requirements for distribution lines

Gas System Installation

Gas Service and Distribution

Gas Meter and Service

• National Grid coordination for service availability
• Meter location: Accessible, minimum clearances from openings
• Service line sizing: Based on total BTU demand calculation
• Pressure testing: Required at 10 PSI for 15 minutes minimum
• Regulator installation: Required for high-pressure services

Interior Gas Distribution

• Main distribution: 1" black iron pipe typical
• Branch lines: 3/4" to 1/2" depending on appliance demand
• CSST flexible connector: Approved for interior distribution
• Shut-off valves: Required within 6 feet of each appliance
• Sediment trap: Required for all gas appliances

Appliance Connections

Kitchen Appliances

• Gas range: 1/2" line with shut-off valve behind range
• Gas cooktop: Separate connection from oven if applicable
• Gas grill connection: Outdoor quick-connect for portable grills
• Flexible connectors: Approved stainless steel only

HVAC and Water Heating

• Furnace connection: Sized for BTU input of equipment
• Water heater: 3/4" line typical for residential units
• Fireplace: Gas log sets require separate venting and gas line
• Pool heater: Sized for high BTU demand equipment

Rough-In Installation Process

Underground and Foundation Work

Under-Slab Installation

• Water service entry: Sleeve through foundation wall
• Sewer line installation: Proper slope and bedding material
• Cleanout installation: Required every 100 feet and at direction changes
• Pressure testing: All underground lines before concrete pour
• Protection: Proper covering and marking of buried lines

Foundation Penetrations

• Sleeve installation: Oversized for thermal movement
• Waterproof sealing: Prevent water infiltration
• Support systems: Prevent pipe settlement and stress
• Insulation: Prevent freezing in foundation penetrations

In-Wall Rough-In

Supply Line Installation

• Pipe routing: Through framing members, adequate support
• Nail plate protection: Where pipes within 1.25" of edges
• Insulation placement: Between supply lines and exterior walls
• Test plugs: Install for pressure testing before covering
• Shut-off valve locations: Accessible but concealed

Drain and Vent Installation

• Main stack installation: Plumb and properly supported
• Branch drain routing: Maintain proper slope throughout
• Vent connections: Proper grade and connection methods
• Cleanout access: Required at base of stacks and direction changes
• Fire stopping: Required at floor and ceiling penetrations

Testing and Inspection Requirements

Pressure Testing Procedures

Water Supply Testing

• Test pressure: 150 PSI for 2 hours minimum
• Visual inspection: Check all joints and connections
• Pressure gauge: Certified and properly calibrated
• Test documentation: Required for inspection approval
• Repair procedures: Address any leaks before covering

Drainage System Testing

• Water test: Fill system to overflow level of highest fixture
• Air test: 5 PSI for 15 minutes with no pressure loss
• Smoke test: Alternative method for detecting leaks
• Final test: After all fixtures installed and operational

Inspection Process

Rough-In Inspection Requirements

• Schedule inspection after rough-in completion
• All systems tested and approved by plumber
• Permit posted and accessible to inspector
• Licensed plumber present during inspection
• Approved plans available for reference

Common Inspection Issues

• Inadequate pipe support and protection
• Improper slope on drainage lines
• Missing or improperly installed venting
• Incorrect fixture rough-in dimensions
• Inadequate pressure testing documentation

Energy Efficiency and Water Conservation

High-Efficiency Systems

• Low-flow fixtures: Reduce water consumption
• Hot water recirculation: Instant hot water delivery
• Tankless water heating: On-demand hot water production
• Greywater systems: Reuse water for irrigation
• Smart leak detection: Prevent water damage and waste

Insulation and Heat Recovery

• Pipe insulation: Reduce heat loss in distribution
• Heat recovery systems: Capture waste heat from drains
• Smart controls: Optimize system operation
• Solar pre-heating: Renewable energy integration

Successful Boston ADU plumbing rough-in requires careful coordination with existing infrastructure, strict adherence to local codes, and quality installation practices. Working with licensed plumbers familiar with Boston's requirements ensures your ADU plumbing system provides reliable service while meeting all regulatory standards. Investment in proper plumbing infrastructure supports both functionality and long-term value.

Quality plumbing rough-in establishes the foundation for efficient, reliable water and waste systems that serve ADU residents comfortably for decades.