North Carolina · 15A NCAC 18E
The North Carolina Department of Health and Human Services On-Site Water Protection Branch writes the rules; county health departments issue permits and perform soil evaluations.
Minimum tank
One to three bedroom dwelling.
Design flow
Held two days for settling.
Cost index
Regional labour and permits.
Sets the design flow and the legal minimum.
Code sizes on bedrooms, not people.
Used to size the matching drainfield. Unsure? Sandy loam is the common default.
Three provinces. Coastal plain sand with a high water table in the east, piedmont clay through the centre, and mountains with thin soil over rock in the west. Each drives a different design approach.
Conventional trenches in the piedmont with generous sizing for clay. Low pressure pipe systems are very widely used in North Carolina — more than in most states — because they distribute effluent shallowly and evenly in tight soils. Coastal counties use fill and mound systems for water table separation.
| Dwelling | Design flow | Minimum tank | With disposal |
|---|---|---|---|
| 1 bedroom | 240 gpd | 1,000 gal | 1,250 gal |
| 2 bedrooms | 240 gpd | 1,000 gal | 1,250 gal |
| 3 bedrooms | 360 gpd | 1,000 gal | 1,250 gal |
| 4 bedrooms | 480 gpd | 1,250 gal | 1,500 gal |
| 5 bedrooms | 600 gpd | 1,500 gal | 1,750 gal |
North Carolina issues an Improvement Permit based on soil evaluation, then a Construction Authorization, then an Operation Permit after inspection. The soil evaluation classifies the site into suitable, provisionally suitable, or unsuitable, and that classification determines everything downstream.
The state sets a floor. These North Carolina counties are where the largest septic populations sit, and where local requirements most often exceed it.
| County | What makes it different |
|---|---|
| Wake | Raleigh area; heavy septic use on piedmont clay |
| Mecklenburg | Charlotte fringe development |
| Union | Rapid growth with clay soils and large required fields |
| Brunswick | Coastal growth, high water table |
| Johnston | Fast-growing county east of Raleigh |
| Buncombe | Asheville; steep slopes and shallow rock |
A three-bedroom home at 120 gallons per bedroom produces 360 gallons per day of design flow. On sandy loam that needs roughly 600 square feet of absorption area. On clay loam it rises to about 1,800 square feet, and on clay a conventional field is usually not permitted at all. Run your own soil class through the drainfield calculator.
Operation permits for advanced systems require ongoing management by a certified operator. Use the pump schedule calculator to work out the interval for your tank size and household.
Regional labour and permit costs in North Carolina run about 94% of the national baseline. Here is what typical installations land at for a three-bedroom home:
| System type | Typical installed cost in North Carolina | When it applies |
|---|---|---|
| Conventional gravity | $8,500 – $15,000 | Good soil, adequate depth to water |
| Chamber system | $9,400 – $17,200 | Alternative to gravel trenches |
| Mound system | $16,200 – $31,500 | Shallow water table or thin soil |
| Aerobic treatment | $13,600 – $27,000 | Clay soil or small lots |
| Tank pump-out (service) | $300 – $610 | Every 3–5 years |
Replacing an existing system costs more than these figures — old-system removal and re-permitting add to every line. The replacement cost calculator covers that case, and the cost estimator adjusts all of the above for your bedroom count and soil.
Verify before you build. The figures above are state minimums compiled for planning, drawn from 15A NCAC 18E, Sewage Treatment and Disposal Systems. County and health district rules routinely exceed them, code text changes, and only North Carolina DHHS — On-Site Water Protection or your local health department can confirm what applies to your parcel.
Send your sizing numbers to installers who work under North Carolina rules every day.