Casita additions are becoming increasingly popular across Arizona. Whether you’re building for extended family, rental income, or extra living space, these small structures offer major value. But before you begin construction, there’s one key system that needs your attention—your septic.

If your property runs on septic, adding a casita with plumbing will affect how your system operates. Arizona has specific guidelines to make sure septic systems are designed to handle the increase in daily use.

How a Casita Addition Impacts Your Septic System

Any time a casita addition includes plumbing like a bathroom or kitchenette, your property’s wastewater flow increases. Arizona law requires your septic system to be sized appropriately based on that added flow. Even a small addition can push your existing system past its limit.

The County will require updated site plans and flow calculations before approving your build. Depending on the size and location of the casita addition, you may need a larger tank, an expanded disposal field, or a brand-new system.

Why a Separate System Might Be a Smarter Option

A second septic system is often the right solution when the existing system is too far away or already near capacity. Running long sewer lines from a detached casita to the main home can add unnecessary expense and future headaches.

In many cases, building a dedicated system for the casita addition makes more sense. It provides flexibility, simplifies maintenance, and keeps usage separated—especially helpful if you plan to rent the space or live in it full time.

We Handle All the Permitting for Your Casita Addition

Before construction starts, you’ll need County approval for any septic changes. At HomeField Onsite Environmental, we take care of the entire permitting process. We’ll evaluate your property, handle system design, submit documents, and communicate directly with the County to keep your project on track.

No surprises, no red tape. Just a smooth process from planning to installation.

Start with a Septic Evaluation Before You Build

If you’re thinking about a casita addition, contact our team first. We’ll review your current septic setup, determine whether you need upgrades or a new system, and guide you through every step.

Building a casita is a smart investment, but it needs the right support underground. Let HomeField make sure your system is ready.