Casita additions are becoming more popular than ever across Arizona. Whether it’s a guest house, an in-law suite, or an income-generating short-term rental, a casita adds flexibility and value to your property. But before you pour the slab or start framing walls, there’s one critical system you can’t overlook: your septic.
If your home is on septic and you’re planning to build a casita, the added flow and use could significantly impact your system. Arizona sets specific rules for sizing and designing septic systems when you add structures like a casita.
What Arizona Law Says About Casita Additions and Septic
In Arizona, adding a detached structure that includes plumbing—such as a toilet, shower, or kitchen sink—triggers a reevaluation of your existing septic system. It’s not as simple as tapping into the line and calling it good.
The Arizona Department of Environmental Quality (ADEQ) requires that any additions creating additional wastewater flow must be properly reviewed and permitted. This includes calculating the daily design flow based on the number of bedrooms and plumbing fixtures on the property.
Even if your main house already has an approved system, a casita can change everything. You may need to upgrade your tank size, expand your disposal field, or even install a separate septic system just for the casita. How you plan to use the new space determines what your system will require.
One Property, Two Tanks?
In some cases, installing a second septic tank and disposal field for the casita addition is the better option. You might need a second system if your existing one lacks capacity or if the casita sits too far from the main home. Running plumbing hundreds of feet to connect to the original system isn’t always practical or cost-effective.
Keep in mind that if you go the route of a separate system, it will need its own set of permits, inspections, and regular maintenance. But for many homeowners, it’s a simpler and more efficient way to accommodate the new living space.
We Handle the Permitting for You
Before construction begins, the County will need to review your site plans, septic system sizing, and in many cases, complete a septic inspection. But you don’t need to take this on alone.
HomeField Onsite Environmental handles the entire septic permitting process on your behalf. We know exactly what the County is looking for, and we’ll make sure your plans check all the boxes before any dirt is moved. That means fewer delays, less stress, and a faster path to building your casita.
What to Do Before You Build
Start with a septic consultation. At HomeField Onsite Environmental, we help homeowners navigate septic system requirements for casita additions every day. We’ll review your current system, help determine if an upgrade or new installation is needed, and make sure your plans are compliant with Arizona regulations.
Casita additions are a smart investment, but they come with important infrastructure decisions. We’re here to make sure your system is ready to handle the added demand so you can build with confidence.
