Septic Capacity in Northern Westchester: When Adding a Bedroom Triggers a System Upgrade

New York State sizes residential septic systems by bedroom count — 150 gallons per bedroom per day — which means most northern Westchester additions that add a bedroom trigger Westchester County Department of Health review of the existing system's capacity. This guide walks through how the bedroom-count rule actually works, what an upgrade costs across gravity and engineered system options, and how to design the project to either avoid the trigger or sequence the upgrade strategically.