Quick answer
If your lot has no public sewer, you need an approved onsite wastewater (septic) system before you can get a building permit. The process starts with a soil evaluation or percolation test, then a system designed and sized for the house, usually by number of bedrooms, and approved by the county health department or state environmental agency. Who can design it depends on your state and the system type.
The septic system can decide where the house goes, how many bedrooms it can have, and even whether a lot is buildable. That is why it belongs at the very start of planning.
The septic permit process
- Soil evaluation: test pits or borings and, in many areas, a percolation test to measure how fast the soil absorbs water.
- System design: tank size and drain field layout sized for the house, commonly based on bedrooms.
- Permit: review and approval by the health department or state agency.
- Installation and inspection: by a licensed installer, inspected before backfilling.
Conventional or alternative system?
A conventional system uses a tank and gravity drain field. Poor soils, high groundwater, shallow rock or small lots may require an alternative system, such as a mound, an aerobic treatment unit or a drip system. Alternative systems usually cost more and need regular maintenance.
Setbacks that shape your site plan
Tanks and drain fields must stay set distances from wells, streams and lakes, property lines, the house and driveways. Many jurisdictions also require a reserve area for a future replacement drain field. Show all of these on your site plan.
Who designs septic systems
Depending on the state and system type, designs may be prepared by a licensed engineer, a licensed septic designer or a sanitarian. Alternative and larger systems more often require an engineer.
What to send us
- Property address and lot survey
- Any soil or percolation test results
- Planned house size and number of bedrooms
- Well location, existing or planned
Get a fixed-fee quote. See civil engineering.
Common questions
What is a perc test?
A test that measures how quickly water soaks into the soil, used to size the drain field and choose the system type.
Can a lot fail a perc test?
Yes. Often an alternative system can still be used, but some lots cannot support any approved system.
Does adding a bedroom affect my septic system?
Usually yes. Adding bedrooms can require a larger system, and many departments check septic capacity before approving additions.
Should I test soil before buying land?
Yes. A failed soil test is one of the most expensive surprises on rural land. See buying land to build.