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The local health department determines the size of the septic tank and drainfield based on the number of bedrooms in the home and the soil conditions on the property. They also evaluate the seasonal high-water table, which helps determine the type of system required (such as a conventional gravity system or a mound system). In some cases, advanced treatment systems may be required, particularly on smaller lots or properties located near lakes, streams, or other sensitive environments.

A conventional gravity septic system typically starts around $10,000, while advanced treatment systems can cost $40,000 or more. The final price depends on factors such as soil conditions, groundwater levels, space constraints, and local health department requirements. In our area, most homes qualify for conventional gravity systems, which generally keeps costs on the lower end of that range. Restoration needs, such as replacing lawns, landscaping, driveways, or other disturbed areas, can add to the overall project cost and are based on site-specific conditions.

When replacing a septic system, the process generally begins with permitting and a site evaluation. Providing an accurate price before this step is difficult because each property is unique and may have different design and regulatory requirements. After the site evaluation and percolation (perc) test are completed in coordination with the local health department, a permit is issued based on those findings. At that point, an accurate project quote can be developed.

During the perc test, a 6–7-foot test hole is excavated so the sanitarian can evaluate soil characteristics and assess seasonal high groundwater levels. Soil conditions significantly influence the size and type of system required. For example, medium sand typically requires approximately 200 square feet of drainfield area per bedroom, while heavier soils such as clay or loam absorb water more slowly and may require up to 500 square feet per bedroom. Another important factor is septic tank sizing. A three-bedroom home is typically permitted with a 1,000-gallon septic tank with access riser covers to grade, and an effluent filter. For homes with more than three bedrooms, an additional 250 gallons is generally added per bedroom. If the home has a garbage disposal, an additional 250 gallons is also required. For example, a five-bedroom home with a garbage disposal would typically require a minimum 1,750-gallon septic tank.

–Ryan Carey, Carey-Sodergren Inc.

Condensation on ceilings where outer walls meet interior walls after new roof/insulation suggests a potential issue with air sealing or bridging of the original layer of insulation. Hot air wants to rise and it can rise and escape out at top plates (the top of interior or exterior walls). If the interior top plate is a double top plate where it meets that exterior wall it could also cause the original layer of insulation to be bridged, or not lay flat against the drywall. Bridged insulation and top plates that are not air sealed cause a cold surface. The warm moist air from inside the house will hit the cold surface and condense.

I would recommend air sealing top plates and ensure good insulation contact. That will be difficult with new insulation added and depending on how much of the original is bridged it may be best to remove that section of insulation to start fresh.

–Amanda Godward, Ecotelligent Homes

To best understand an accurate replacement cost you will need an issued permit from your local health department. Contact your local health department to obtain a permit application (some health departments have these forms online). Submit a “Septic Replacement” application. The health department will conduct an onsite visit to obtain property features, measure for required offsets, and conduct a soil analysis. Some health departments and certain soils require a backhoe cut. This practice would require having a contractor onsite with the necessary equipment to expose the soil profiles (an approximately 7 foot hole) for the onsite sanitarian. When the sanitarian has all of this information they will design and list out the requirements for the drainfield replacement. This is what makes up the permit. Once you have the permit you can share that with a contractor(s) to receive a quote and scope of work.

–Nick Routley, Routley’s Inc.