PLUMBING
How to Estimate a Septic System Installation
Contractor method for estimating septic systems: bedrooms, tank, drain field, soil and permits.
Septic bids depend on the dirt you cannot see. The tank is predictable; the percolation test and the drain field are where estimates go sideways.
THE SHORT ANSWER
How do you estimate a septic system?
Size by bedrooms, run the percolation test to pick the field type, price the tank, field, excavation and access, then add testing and permits. A 3-bedroom conventional system runs $10,000-$14,000.
Size by bedrooms
Local codes size the tank and field by bedroom count. A 3-bedroom home needs a 1,000-gallon tank and a conventional field; 4-5 bedrooms push both up.
Run the soil test first
The percolation test determines the field type: conventional, pressure distribution or mound. Poor soil raises the field cost 15-40%. Never quote without the test result.
Price tank, field, excavation and access
Concrete tanks run $1,500-$4,500; plastic is ~10% cheaper. Fields run $3,000-$12,000 depending on type. Tight access adds $500-$1,000 for the excavator.
Add testing, permits and check
Percolation tests run $300-$900, health permits $500-$1,500. Use the Septic System Cost Calculator and stay within 10% before markup.