Bedroom count is not just a real estate number in Pima County. It is the figure your septic system was originally sized around, and adding a bedroom to a home that is not on the sewer means the county wants to know that the existing system can actually handle the extra load before it approves your building permit. If you are planning an addition and your house is on septic, this is worth understanding before your architect finalizes the plans, not after.
When your septic system was originally permitted, the design was based on an estimated daily wastewater flow tied to the number of bedrooms in the house at the time, since bedroom count is used as a stand in for how many people are likely to live there and how much water they will use. A three bedroom house and a five bedroom house on the same lot generate very different flows into the same size tank and drainfield. Add two bedrooms without touching the system, and you can end up asking a septic system designed for a smaller household to handle meaningfully more wastewater than it was built for.
When you apply for a building permit for an addition that increases bedroom count on a property served by an onsite wastewater system, Pima County's review typically wants documentation that the existing septic system can support the new bedroom total, or a plan to upgrade it if it cannot. Exactly what is required depends on your specific system and the size of the addition, and this is coordinated through the same permitting process that ADEQ and Pima County Environmental Quality oversee for septic systems generally. Our ADEQ inspection guide covers how that office handles septic permitting more broadly.
Pull or review the original permit record. Older Tucson properties sometimes have septic permits on file with the county showing the original design flow and bedroom basis, which tells us immediately whether there is room to add bedrooms or not.
Inspect the existing system. Beyond just the paperwork, we look at the actual condition of the tank and drainfield, since a system on paper for four bedrooms that has been poorly maintained may not perform like a healthy four bedroom system in practice. Our what fails a septic inspection page covers the common problems we find.
Tell you what your options are. Sometimes the existing system already has enough capacity and no changes are needed. Sometimes a larger drainfield or an additional tank resolves it. In rare cases involving a small lot, the sizing question can affect how big an addition is practical at all, which is much better to know before you have paid for architectural drawings.
The earlier this gets checked, the less it affects your schedule. Ordering a system evaluation while your addition is still in the design phase means any needed septic work can be scoped and bid alongside the rest of the project, rather than surfacing as a surprise after the building permit application is already submitted. See our inspection cost guide for what a system evaluation runs.
An undersized system for a growing bedroom count is a repair and upgrade project, not a full replacement in most cases. Our septic repair page covers what that work typically involves, and how it gets sequenced with the county's review of your addition.
Call (520) 389-5764 with the current bedroom count, what you are adding, and the age of the septic system if you know it. We will tell you where you stand before you go further into the design.
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Call (520) 389-5764