ADU Septic Systems: Everything You Need to Know Before You Build
Septic Design, Permits & Installation for ADU Projects
Free Site Evaluations & 24/7 Emergency Service
Site & Soil Evaluation
Perc testing and site assessment to determine which septic system your lot can support for your ADU.
Existing System Capacity Check
We evaluate whether your current tank and drain field can handle the additional load from your ADU.
New System Design & Install
From conventional leach fields to advanced ATU systems — we design and install the right solution for your property.
Oregon's Trusted ADU Septic System Specialists
Building an ADU on a property without sewer access? A septic system is not optional — it’s a requirement before your ADU can be permitted or occupied. Our licensed Oregon septic professionals handle everything from soil testing and system design to permits, installation, and DEQ sign-off. We serve Clackamas, Multnomah, Washington, Marion, and Yamhill Counties.
Licensed Septic Contractor • Oregon DEQ Certified
We are fully licensed, insured, and DEQ-certified in Oregon. Our team has completed ADU septic installations across the greater Portland area, navigating county-specific requirements so you don’t have to.
ADU Septic Services We Provide
Permit & DEQ Clearance
We manage OWTS applications, Environmental Health submissions, and all county-specific permit requirements.
Pumping & Ongoing Maintenance
Post-build septic pumping, annual inspections, and maintenance to keep your ADU system running long-term.
Step 1: Free Site Evaluation
We assess your lot, soil conditions, existing system, and setback requirements to determine feasibility.
Step 2: System Design & Permitting
We design your system and handle all permit applications, perc tests, and Environmental Health clearances.
Step 3: Licensed Installation
Our DEQ-certified contractors install your system to code, with full inspection coordination included.
Ready to Build Your ADU? Start With Septic
Get your ADU septic system designed, permitted, and installed by Oregon’s trusted septic professionals.
Contact us for a free site evaluation!
Our ADU Septic Installation Process
Step 4: Final Sign-Off & Documentation
We deliver your as-built drawing and permit documentation so your ADU build can move forward without delays.
Get A Clear Quote
We provide upfront, transparent pricing over the phone for the septic services you need. We’ll inform you of what to expect so there are no surprises!
Schedule Your Services
Our team will work with you to schedule your septic services, arrive on time, and keep you updated along the way!
We Handle the Dirty Work
From plans and permits to installations and repairs, our experienced team will take care of it all! Rest assured, you're in good hands with Lil’ Stinky.
When You Need ADU Septic Help Now
Some ADU septic situations can’t wait. If any of the following apply to your project, reach out now — delays can hold up your entire ADU build timeline.
No Sewer Access on Your Property
If your property is not connected to a municipal sewer line, a septic system is required before your ADU can be permitted. We’ll assess your lot and get the process started right away.
Existing System Lacks Capacity
Adding an ADU increases your daily wastewater load. We assess whether your existing tank and drain field can handle the extra flow — or whether an upgrade or new system is needed.
Permit Application Requires Septic Clearance
Most Oregon counties require Environmental Health clearance before issuing a building permit for an ADU with a septic system. We handle the evaluation, design, and submission to keep your project moving.
System Showing Signs of Failure
Slow drains, pooling water, or foul odors near your drain field are warning signs your system needs immediate attention — especially before adding the load of an ADU.
Get Your ADU Septic Evaluation — Fast
Fast, licensed ADU septic services when your build schedule depends on it.
Call us today!
7 Things Your ADU Septic Contractor Must Do
1. Conduct a Full Site & Soil Evaluation
Before any system is designed, we evaluate soil conditions, lot boundaries, setback distances, water table depth, and proximity to wells or water features to determine what system your property can support.
2. Assess Your Existing System's Capacity
We calculate whether your existing septic tank and drain field have sufficient capacity for the added wastewater load from your ADU — typically around 150 gallons per day for a one-bedroom unit.
3. Select the Right System Type for Your Lot
From conventional leach fields and seepage pits to advanced aerobic treatment units (ATUs) and mound systems — we match the system type to your soil, lot size, budget, and local county regulations.
4. Handle All Permits & DEQ Clearances
We manage the full permitting process including OWTS clearance, percolation testing coordination, system design submission, and final inspection sign-off. You won’t be left navigating county offices alone.
5. Produce an Accurate As-Built Drawing
Every installation includes a detailed site diagram showing the system’s location, components, and setback distances — required documentation for your permit file and future property transactions.
6. Complete Installation to Code
Our licensed contractors install every system to Oregon DEQ standards and local county requirements. All work is inspected and signed off before your ADU building permit proceeds.
7. Provide Ongoing Maintenance Support
We don’t disappear after installation. We offer ongoing pumping, inspection, and maintenance services to keep your ADU septic system running reliably for decades. Pump every 3–5 years, inspect annually.
See Our ADU Septic Work in Action
Areas We Serve
Our licensed septic team provides ADU septic design, installation, and maintenance across Oregon. Contact us for a free evaluation and quote!
- Clackamas County
- Multnomah County
- Washington County
- Marion County
- Yamhill County
- Lane County
- Polk County
- Benton County
- Jackson County
- Linn County
Frequently Asked Questions About ADU Septic Systems
What permits are required to install a septic system for an ADU in Oregon?
Any new or expanded septic system in Oregon requires a permit from your county’s Environmental Health department — separate from your ADU building permit. Your county will typically require a site evaluation, percolation test, and a system design by a licensed engineer. We manage this entire process for you.
Can my ADU connect to my existing septic system?
Yes, in many cases — but only if your existing tank and drain field have enough capacity for the added load. A one-bedroom ADU typically adds around 150 gallons per day. We assess your current system’s design specs and compare them against projected ADU flow rates before recommending a path forward.
What is the minimum lot size needed for an ADU septic system in Oregon?
Oregon does not set a single statewide minimum lot size. Each county sets its own requirements based on soil type, water table, and proximity to water sources. In general, you need enough usable land to accommodate the drain field, required setbacks, and a designated replacement drain field area. Contact us for a county-specific evaluation.
Which septic system type is best for an ADU — conventional, ATU, or other?
The right system depends on your soil conditions, lot size, local county regulations, and budget. Conventional leach field systems are the most affordable and work well on lots with good soil percolation. Advanced treatment units (ATUs) are required on smaller lots, near water bodies, or where soil conditions don’t support a conventional system. We evaluate your property and recommend the best fit.
How much does an ADU septic system cost in Oregon?
Costs vary depending on whether you need a capacity evaluation, an upgrade, or a full new installation. Percolation testing runs $500–$2,000. Tying into an existing system typically costs $2,000–$8,000. A new conventional system runs $8,000–$20,000, and advanced treatment systems can reach $15,000–$35,000+. Permit fees add $500–$3,000 depending on your county.
How long does the ADU septic installation process take?
The timeline is mostly driven by permitting, not installation. Soil and perc testing takes 1–3 weeks. Permit approval typically takes 4–12 weeks. Installation itself takes 1–5 days. Final inspection and sign-off adds another 1–3 weeks. Plan for 2–5 months total. Starting your septic evaluation at the same time as your ADU design prevents costly delays.
Committed to Getting Your ADU Septic System Right
