Water, Sewer & Septic

Septic System Design

Engineered septic system design for new homes, additions and failed systems, including alternative and mound systems. Typical US fees run $1,000 to $3,000, and most projects take 2 to 8 weeks including health department review. Our drawings, calculations and reports are sealed by a Professional Engineer (PE) licensed in the state where your project is located, ready for permit submission.

Typical US fee$1,000 to $3,000

Typical timeline2 to 8 weeks including health department review

Permit drawingsSealed by a PE

What the work involves

A septic designer or civil engineer uses soil and perc test results to size the tank and drain field, select a conventional or alternative system (mound, aerobic, drip, sand filter) and prepare plans for the health department. Who may design depends on the state: some allow licensed septic designers or soil scientists, while engineered alternative systems often need a PE.

When you need it

Building on a lot without public sewer
Adding bedrooms or an ADU
Existing system failed
Perc test results rule out a conventional system
Health department requires engineered plans

What you receive

Septic design plans
Sizing calculations
Health department permit application
Installation inspection or certification

What drives the cost

HomeGuide puts engineering and design fees at $1,000 to $3,000; Building Advisor reports $500 to $1,200 for conventional designs and more for alternative systems. Installation is separate (HomeGuide: mound systems $25,000 to $50,000 or more).

Related calculators

Septic Tank Size CalculatorEstimate a residential septic tank size from the number of bedrooms using a common 1,000 gallon minimum plus 250 gallons per extra bedroom.

Frequently asked questions

How much does septic System Design cost?

Across the US, septic System Design usually costs $1,000 to $3,000. HomeGuide puts engineering and design fees at $1,000 to $3,000; Building Advisor reports $500 to $1,200 for conventional designs and more for alternative systems. Installation is separate (HomeGuide: mound systems $25,000 to $50,000 or more).

How long does septic System Design take?

Plan on 2 to 8 weeks including health department review from signed proposal to stamped deliverables, longer if a site visit, soil testing or a permit review cycle is involved.

Do I need a licensed PE for septic System Design?

In most US jurisdictions, yes. When the work needs a permit, the plans, calculations or report usually must be sealed by a Professional Engineer licensed in the state where the project is located. Every deliverable we issue for permit is sealed that way.

Will I also need a soil scientist?

Sometimes. Depending on the site, septic System Design can also involve a soil scientist, septic designer, septic installer or land surveyor. We tell you up front which other professionals your project needs and coordinate with them so the drawings agree.

Who do you provide septic System Design for?

Most of our clients for this service are homeowners, contractors and developers. Describe your project and one of our engineers will reply with scope, fee and schedule.

Do I need an engineer for a septic system?

It depends on your state. Some allow licensed septic designers for conventional systems; alternative systems often require a PE.

Why do some lots need mound systems?

Shallow bedrock, high water tables or slow-draining soils prevent conventional drain fields. A mound raises the treatment area above the limiting soil layer.

How long do septic systems last?

With maintenance, many systems last decades; EPA recommends pumping typically every three to five years. Alternative systems with pumps or aerators need regular servicing as well.

Who approves the design?

Usually the county or state health department. Some states also require the designer to inspect the installation.