Septic system requirements in Idaho
What landplan.io applies when it designs a septic system in Idaho: the system types allowed, tank sizes, setbacks and soil loading rates, with what septic products cost there.
Updated
Design a septic system for an address in Idaho
Reviewed landplan.io designs by Idaho's own rules, which our staff reviewed against the state's regulations. Last published 5 October 2026.
Septic systems allowed in Idaho
The system types landplan.io permits in Idaho:
- Elevated Sand Mound System
- Subsurface Pressure Trench System
- Subsurface Trench System
- Infiltrator Advanced Treatment Leachfield
- Infiltrator Advanced Enviro-Septic® (AES)
- Discharging System
Septic tank size in Idaho
The daily design flow of a home: 150 gal/day per bedroom, at least 240 gal/day. The septic tank is sized from that flow:
| Daily design flow | Minimum tank |
|---|---|
| up to 240 gal/day | 1,000 gallons |
| 240 to 360 gal/day | 1,500 gallons |
| 360 to 600 gal/day | 2,000 gallons |
| 600 to 720 gal/day | 2,500 gallons |
| 720 to 840 gal/day | 2,750 gallons |
| 840 to 920 gal/day | 3,000 gallons |
| 920 to 1,040 gal/day | 3,250 gallons |
Septic setbacks in Idaho
| From | To | Distance |
|---|---|---|
| Polygon | Existing Septic Component to be Abandoned | 5 ft |
These are the values the landplan.io design engine applies in Idaho. Confirm a design with the Idaho health department or your county's before you build.
Parcel data in Idaho
landplan.io has parcel boundaries for 40 of Idaho's 44 counties, and part of 4 more: the counties where 97.6% of the state's people live. Type an address there and the design starts from the parcel.
Septic companies, designers and jobs in Idaho
Where the rules come from
The regulations and documents landplan.io's Idaho rules are read from:
Septic rules by county in Idaho
- Ada County
- Adams County
- Bannock County
- Bear Lake County
- Benewah County
- Bingham County
- Blaine County
- Boise County
- Bonner County
- Bonneville County
- Boundary County
- Butte County
- Camas County
- Canyon County
- Caribou County
- Cassia County
- Clark County
- Clearwater County
- Custer County
- Elmore County
- Franklin County
- Fremont County
- Gem County
- Gooding County
- Idaho County
- Jefferson County
- Jerome County
- Kootenai County
- Latah County
- Lemhi County
- Lewis County
- Lincoln County
- Madison County
- Minidoka County
- Nez perce County
- Oneida County
- Owyhee County
- Payette County
- Power County
- Shoshone County
- Teton County
- Twin Falls County
- Valley County
- Washington County
Questions
What septic systems are allowed in Idaho?
landplan.io permits these system types in Idaho: Elevated Sand Mound System, Subsurface Pressure Trench System, Subsurface Trench System, Infiltrator Advanced Treatment Leachfield, Infiltrator Advanced Enviro-Septic® (AES) and Discharging System.
What size septic tank do I need in Idaho?
landplan.io sizes the septic tank in Idaho from the daily design flow: up to 240 gal/day: 1,000 gallons; 240 to 360 gal/day: 1,500 gallons; 360 to 600 gal/day: 2,000 gallons; larger flows need larger tanks. A home's design flow is 150 gal/day per bedroom, at least 240 gal/day.
Does landplan.io have parcel data in Idaho?
Yes, for 40 of Idaho's 44 counties, and part of 4 more.