How Much Does a Separate Sewer Lateral Connection Cost for an ADU?

Understanding ADU Sewer Lateral Costs in California

Of all the utility-related costs in an ADU project, the sewer lateral connection is often the most expensive and the most unpredictable. A separate sewer lateral can cost anywhere from $5,000 to $25,000 or more, depending on your property's location, the distance to the city sewer main, and local requirements. For many homeowners, this single line item can add 10% to 15% to the total project budget.

In this guide, we will explain what a sewer lateral is, when you need a new one for your ADU, how costs are calculated, and what alternatives might be available. If you are in the budgeting phase of your ADU project, this information will help you avoid one of the most common and costly surprises.

What Is a Sewer Lateral?

A sewer lateral is the underground pipe that connects a building's plumbing system to the public sewer main, which is typically located under the street. Every home connected to a municipal sewer system has a sewer lateral. The lateral runs from your home's plumbing (usually exiting the foundation) across your property, under the sidewalk, and connects to the sewer main in the street.

Anatomy of a Sewer Lateral System

• Building drain: The pipe inside your home that collects wastewater from all fixtures
• Building sewer: The portion of the lateral on your property, from the foundation to the property line
• Public sewer lateral: The portion from the property line to the sewer main (ownership and maintenance responsibility varies by city)
• Sewer main: The large public sewer pipe in the street (owned and maintained by the city or sewer authority)
• Cleanout: An access point for inspection and cleaning, typically located near the property line

When Is a Separate Sewer Lateral Required?

Whether you need a separate sewer lateral for your ADU depends on several factors:

State Law Protections

As mentioned in our guide on ADU utility hookups, California law prohibits requiring new sewer connections for ADUs under 750 square feet. This means that for smaller ADUs, you have the right to connect to your existing sewer lateral.

When a Separate Lateral May Be Required

Scenario	Separate Lateral Required?	Explanation
ADU under 750 sq ft, shared lateral	No (protected by state law)	Must allow connection to existing lateral
ADU 750+ sq ft, city requires it	Yes	Subject to local sewer authority rules
Existing lateral is in poor condition	May be required	City may require replacement as condition of permit
Existing lateral is undersized	Possible	Older 3-inch laterals may need upgrade to 4-inch
Property is on septic	Connection to sewer may be required	If sewer is available within a certain distance

Sewer Lateral Cost Breakdown

The total cost of a sewer lateral connection includes several components. Let's break down each one:

Cost Components

Cost Component	Typical Range	Notes
Sewer connection permit	$500 to $2,000	Varies by city
Pipe material and installation (on property)	$50 to $150 per linear foot	Depends on depth and soil conditions
Pipe material and installation (under street)	$150 to $300 per linear foot	Includes traffic control, excavation
Connection to sewer main (tap)	$1,000 to $3,000	Saddle or direct connection
Street and sidewalk restoration	$2,000 to $8,000	Asphalt, concrete, and compaction
Video inspection (pre and post)	$200 to $500	May be required by city
Sewer capacity / connection fee	$0 to $5,000	Exempt for ADUs under 750 sq ft
Backyard landscape restoration	$500 to $3,000	Depends on what was disturbed

Sewer Lateral Costs by California City

Sewer connection costs and requirements vary by city. Here is what homeowners typically face in major California metros:

City	Sewer Authority	Estimated Total Cost	Key Notes
Los Angeles	LA Bureau of Sanitation	$8,000 to $20,000	Separate lateral often required for 750+ sq ft ADUs
San Diego	City of San Diego PUD	$7,000 to $18,000	Capacity charge may apply
San Francisco	SFPUC	$10,000 to $25,000	Higher costs due to density and utilities
Oakland	EBMUD (sewer varies)	$6,000 to $15,000	Shared laterals commonly accepted
Long Beach	Long Beach Water Dept	$5,000 to $12,000	More moderate costs, efficient process
Pasadena	Pasadena Water and Power	$6,000 to $14,000	Standard residential rates apply
Sacramento	Sacramento Area Sewer Dist.	$5,000 to $12,000	ADU-friendly fee structure

Alternatives to a Separate Sewer Lateral

If a separate sewer lateral would be prohibitively expensive, consider these alternatives:

1. Tie Into the Existing Lateral

For ADUs under 750 square feet, California law requires that you be allowed to connect to your existing sewer lateral. Even for larger ADUs, some cities will allow a shared lateral if it is in good condition and adequately sized (4 inches or larger).

Cost savings: $5,000 to $20,000 compared to a new lateral

2. Install a Cleanout and Video Inspection

If your city is concerned about the condition of your existing lateral, you can often address those concerns by installing a new cleanout and conducting a video inspection. If the inspection shows the lateral is in good condition, the city may approve the shared connection.

Cost: $500 to $1,500

3. Sewer Lateral Lining

If your existing lateral is in poor condition but otherwise adequate in size, trenchless pipe lining (also called cured-in-place pipe or CIPP) can rehabilitate the pipe without excavation. This is often much cheaper than full replacement.

Cost: $4,000 to $8,000

4. Sewage Ejection Pump

In some cases where the ADU is located below the existing sewer lateral grade, a sewage ejection pump can lift wastewater to the level of the existing lateral. While this adds a mechanical component to the system, it can be significantly cheaper than running a new lateral.

Cost: $2,000 to $5,000 installed

The Sewer Lateral Installation Process

Understanding the process helps you plan for the timeline and disruption:

1. Sewer video inspection (existing lateral): Determines current condition and identifies connection points. Takes 1 to 2 hours. Cost: $200 to $400
2. Permit application: Apply for sewer connection permit from your city's sewer authority. Timeline: 1 to 4 weeks
3. Utility locating (811/DigAlert): Mark all underground utilities before excavation. Required by law, free service, 2 business day minimum lead time
4. Excavation: Dig the trench for the new lateral pipe. On your property and under the street. Depth is typically 3 to 8 feet depending on the sewer main depth
5. Pipe installation: Install 4-inch (minimum) ABS or PVC pipe at the correct grade (typically 1/4 inch fall per foot)
6. Connection to sewer main: A saddle tap or direct connection to the main pipe. Often requires traffic control and lane closure
7. Inspection: City inspector verifies correct installation, grade, and connections
8. Backfill and compaction: Fill the trench with suitable material and compact
9. Street and sidewalk restoration: Restore any pavement, sidewalk, or curb that was disturbed
10. Final video inspection: Some cities require a post-installation video to confirm proper installation

Total timeline: 3 to 7 business days for the physical work, plus permit processing time

Choosing a Sewer Lateral Contractor

Sewer lateral work requires specific licensing and expertise. Look for these qualifications:

• C-36 Plumbing Contractor license: Required for sewer lateral work in California
• Encroachment permit experience: The contractor should be familiar with working in the public right-of-way
• Insurance: Adequate liability insurance (at least $1 million) and workers' compensation
• City-specific experience: Contractors who regularly work with your city's sewer authority know the process and requirements
• References: Ask for references from recent sewer lateral projects in your area

Budget Planning Tips for Sewer Laterals

1. Get a video inspection first: Before budgeting for a new lateral, have your existing lateral inspected. A $300 inspection could save you $15,000 if the existing lateral is in good condition
2. Keep your ADU under 750 sq ft if possible: This eliminates the city's ability to require a separate connection
3. Ask about the sewer main location: Your city's public works department can tell you which side of the street the sewer main is on. If it is on your side, costs will be lower
4. Consider ADU placement: Locating the ADU closer to the existing sewer lateral or sewer main can reduce pipe length and cost
5. Budget 20% contingency: Sewer work often encounters surprises underground, so pad your budget accordingly
6. Coordinate with construction: If possible, have sewer work done during the early phase of ADU construction when equipment is already on site

Frequently Asked Questions

Who owns and maintains the sewer lateral?

In most California cities, the property owner owns and is responsible for maintaining the sewer lateral from the house to the connection at the sewer main. Some cities have lateral replacement programs or cost-sharing arrangements. Check with your city's sewer authority for specific policies.

Can I do sewer lateral work myself?

No. Sewer lateral installation and connection to the public sewer main requires a licensed plumbing contractor (C-36 license) and permits from the city's sewer authority. Unauthorized work on sewer connections is illegal and can result in fines.

How long does a sewer lateral last?

A properly installed sewer lateral should last 50 to 100 years depending on the pipe material. Modern PVC and ABS pipes have the longest expected lifespan. Older clay or cast iron pipes may need replacement sooner.

Will my existing lateral handle the additional flow from an ADU?

A standard 4-inch residential sewer lateral can typically handle the flow from a main house plus an ADU. However, if your existing lateral is only 3 inches (common in very old homes), an upgrade may be needed. A plumbing contractor can evaluate your specific situation.

Conclusion

Sewer lateral costs are one of the most significant variables in ADU project budgets. The total cost depends on whether you can share your existing lateral, the distance to the sewer main, street restoration requirements, and local fees. For ADUs under 750 square feet, California law protects your right to share the existing lateral, which can save $5,000 to $20,000.

If a separate lateral is required, budget $8,000 to $20,000 for the work and plan for 2 to 4 weeks of additional project time. Working with an experienced plumbing contractor and coordinating the sewer work with your overall construction schedule will help minimize both cost and disruption.

For a complete picture of all ADU costs, including other hidden expenses that can surprise homeowners, read our guide on hidden ADU costs before breaking ground.

Tips for Working with Plumbers on ADU Sewer Connections

Your plumber is a critical partner in the sewer connection process. Here is how to get the best results and avoid common problems.

• Hire a plumber with ADU sewer experience: Not all licensed plumbers have experience with sewer lateral installations. ADU sewer work often involves city permitting, coordination with the main sewer line, and compliance with specific local standards. Ask candidates how many ADU sewer connections they have completed and request references
• Get a sewer camera inspection first: Before any work begins, have your plumber run a camera through the existing sewer lateral to assess its condition. A camera inspection costs $200 to $400 and can reveal root intrusion, cracks, bellies (low spots where waste collects), and material deterioration. This information helps you plan and budget accurately
• Confirm city permit requirements: Sewer connection permits are separate from building permits in most jurisdictions. Your plumber should know the local requirements, but verify independently that all necessary permits have been obtained before excavation begins. Unpermitted sewer work can result in fines and required removal
• Plan for inspection scheduling: City sewer inspections must be scheduled in advance, and inspectors may only be available on certain days. Coordinate with your plumber and general contractor to ensure the sewer work timeline accounts for inspection windows. A missed inspection can delay backfill and subsequent construction phases
• Discuss cleanout placement: Building code requires accessible cleanout fittings at specific intervals along the sewer line. Discuss cleanout locations with your plumber during the planning phase to ensure they are positioned for easy access without interfering with landscaping, walkways, or the ADU footprint

Common Sewer Issues That Affect ADU Projects

Understanding the most frequent sewer-related problems helps you anticipate and address them before they cause costly delays.

Insufficient Grade (Slope)

Sewer lines require a minimum slope (typically 1/4 inch per foot for 4-inch pipe) to ensure proper flow by gravity. If your lot does not provide enough elevation change between the ADU and the city sewer main, you may need a sewage ejector pump or grinder pump system. Pump systems add $3,000 to $6,000 to the project cost and require ongoing maintenance, but they are a reliable solution for challenging site conditions.

Shared Sewer Laterals

In some older Los Angeles neighborhoods, two or more properties share a single sewer lateral to the city main. If your property has a shared lateral, adding an ADU increases the flow through a line that may already be at or near capacity. You may need to install a separate lateral for the ADU, negotiate shared maintenance agreements with your neighbor, or upgrade the shared line to a larger diameter. Identifying this situation early through a title search and sewer records review is essential.

Root Intrusion

Tree roots are the most common cause of sewer line damage in Southern California. Roots seek out moisture and can penetrate joints in older clay or concrete pipe. If your existing sewer lateral shows root intrusion, you will likely need to address this before connecting the ADU. Options include root cutting (a temporary fix), pipe lining (a trenchless repair method), or full pipe replacement. Pipe lining typically costs $80 to $120 per linear foot and can extend the life of the lateral by 50 years or more.

Orangeburg and Clay Pipe

Homes built before the 1970s often have sewer laterals made of orangeburg (compressed tar paper) or vitrified clay pipe. Both materials deteriorate over time and are prone to cracking, collapse, and root intrusion. If your camera inspection reveals orangeburg or severely deteriorated clay pipe, plan for a full lateral replacement as part of your ADU project. Replacing the lateral now, while excavation equipment is already on site, is significantly cheaper than doing it as a separate project later.

Frequently Asked Questions: ADU Sewer Lateral Connections

How long does it take to install a separate sewer lateral for an ADU?

The physical installation typically takes two to four days, depending on the distance from the ADU to the city sewer main, soil conditions, and whether any obstacles (such as concrete, tree roots, or other utilities) need to be navigated. However, the permitting and inspection process can add two to six weeks to the overall timeline. Plan for a total of four to eight weeks from permit application to completed and inspected installation.

Can I connect my ADU sewer to a septic system instead of the city sewer?

In most urban and suburban areas of Los Angeles County, connecting to the city sewer system is required. Septic systems are generally only permitted in rural or unincorporated areas where city sewer service is not available. If your property is in an area served by public sewer, you must connect to it. For properties on existing septic systems, adding an ADU may trigger a requirement to upgrade or expand the septic system. For more on septic-related considerations, see our guide on ADU septic systems.

Who is responsible for maintaining the sewer lateral from my property to the city main?

In most California cities, the property owner is responsible for the entire sewer lateral from the building to the connection point at the city sewer main in the street. This includes any repairs, replacements, or cleaning needed to keep the line functioning properly. Some cities have sewer lateral replacement programs that offer financial assistance or rebates. Check with your local public works department to see if any assistance programs are available in your area.

What is the difference between a sewer connection fee and the actual installation cost?

The sewer connection fee is a one-time fee paid to your city or sewer district for the right to connect a new unit to the public sewer system. This fee ranges from $2,000 to $8,000 depending on your jurisdiction. The installation cost covers the actual physical work of trenching, laying pipe, and connecting your ADU to the sewer system. Installation costs range from $3,000 to $15,000 depending on distance, depth, and site conditions. You will pay both the connection fee and the installation cost. For a full picture of unexpected project expenses, review our article on hidden ADU costs before breaking ground.

Does trenchless sewer installation work for ADU projects?

Trenchless methods (pipe bursting or pipe lining) can work for ADU sewer connections in certain situations, particularly when replacing an existing deteriorated lateral. Trenchless installation minimizes disruption to landscaping, driveways, and hardscape. However, it requires that the existing pipe path is relatively straight and accessible at both ends. New lateral installations (where no existing pipe exists) typically require traditional trenching. Discuss trenchless options with your plumber to determine if they are feasible for your specific project.