Building a New Home? What to Know Before Designing Your Septic System
If you’re building a new home in New Hampshire, chances are you’ll need a septic system to handle your household wastewater. While things like kitchen layouts and flooring options are exciting to plan, your septic system is one of the most important parts of your home’s infrastructure—and it needs careful attention from the very beginning.
At Townes Septic, we work with homeowners across central NH to design and install septic systems that meet local codes and long-term needs. In this post, we’ll walk you through what to consider before your system is designed and installed, so you can build smart and avoid costly surprises down the line.
Why Septic Design Matters in New Construction
Your septic system is responsible for managing everything that goes down the drains, from showers and laundry to dishwashing and toilet flushing. In new construction, this system must be designed before the home is built—based on soil conditions, household size, and property layout.
A well-designed septic system will:
Treat and dispose of wastewater safely
Support your home’s water usage without overloading
Comply with New Hampshire regulations
Protect your property, groundwater, and investment
Skipping steps or designing without expert input can lead to health hazards, permit delays, and expensive repairs later. Planning ahead ensures your new home starts with a solid foundation—literally and figuratively.
Key Factors in Designing a New Septic System
When designing a septic system for new construction, here’s what to consider:
1. Soil Testing (Perc Test)
Before anything else, a licensed professional must perform a percolation test (perc test) to evaluate your soil’s ability to absorb and treat wastewater. The results help determine:
If your lot is suitable for a septic system
The type of system required (conventional, mound, etc.)
The size and location of the drainfield
2. System Sizing Based on Bedrooms
In New Hampshire, septic systems are typically sized based on the number of bedrooms—not bathrooms or square footage. Why? Because bedrooms indicate potential occupancy, which relates to daily wastewater output.
Your system must be large enough to handle the expected load:
2-bedroom home = smaller system
4+ bedroom home = larger tank and drainfield
Even if you’re building a smaller home now, consider future expansion plans before finalizing your design.
3. Topography and Setbacks
Your property’s slope, ledge, and elevation changes all influence where your system can go. Regulations also require specific setbacks from:
Wells (yours and neighbors’)
Property lines
Water bodies or wetlands
Foundations and driveways
A good septic contractor will work with your builder and surveyor to ensure everything fits within code and works with your building plans.
What to Expect During the Septic Design Process
Designing a septic system involves several coordinated steps:
Site Evaluation & Soil Testing
A licensed designer performs tests and surveys your property to map out the usable area.System Design Plan
Based on the findings, a full septic plan is drawn up. This includes tank size, drainfield layout, piping, and placement.Permitting Process
Your local town or city must review and approve your septic design before issuing a building permit.Installation Coordination
Once approved, your septic contractor schedules the installation to align with your home’s construction timeline.
At Townes Septic, we guide homeowners through each step and ensure every design meets New Hampshire’s state and local requirements.
Septic Design Mistakes to Avoid
Building a home is a big investment. Avoid these common septic system pitfalls:
Designing without a soil test: Always start with proper testing—guesswork leads to failure.
Undersizing your system: Don’t try to cut costs here. A too-small system will back up under normal use.
Ignoring future plans: Planning to finish your basement or add rooms later? Factor that into the initial design.
DIY design or cheap contractors: Septic systems require licensed professionals familiar with local rules.
Why Choose Townes Septic for Your Septic Design & Install?
Our team at Townes Septic is proud to serve homeowners in Weare, Deering, Henniker, Dunbarton, and the surrounding areas. We bring decades of local experience and understand:
New Hampshire’s land and soil
State and town permitting rules
How to design systems that last for decades
We work directly with your builder to coordinate installation timelines and provide expert insights during site planning. Whether you’re building your forever home or a weekend getaway, we’ll help ensure your septic system is built to match.
Frequently Asked Questions About Septic Design
Do I need a permit before installing a septic system?
Yes. In New Hampshire, you must have an approved septic design plan and obtain a permit before any work begins.
How long does septic design take?
It depends on the soil and site complexity, but typically 2–4 weeks from testing to permit submission. Add extra time for approval and installation.
Can I design my own septic system?
No. New Hampshire law requires designs to be submitted by a licensed septic designer. A professional will ensure it meets code and functions properly.
What’s the average cost of a new septic system?
Costs vary widely, but a full design and installation can range from $8,000 to $20,000+ depending on system type and site conditions.
Final Thoughts: Design with Confidence, Build with Peace of Mind
A septic system might not be the flashiest part of your new home, but it’s one of the most important. Taking time to design it correctly from the start will save you money, protect your land, and give your new house the reliable foundation it deserves.
Need help designing a septic system for your new build?
Townes Septic is here to help. From site testing to final installation, we’ll walk you through each step and make sure your system is ready for move-in day—and beyond.
Contact us today to schedule a consultation or ask about septic design for your new home.