Setback

A setback is the minimum distance that a structure must be kept from a lot's boundaries — typically the front, side, and rear property lines, and sometimes from a street or another building. Zoning codes set these distances to preserve light, air, privacy, fire separation, and a consistent street pattern. In practice, setbacks define the buildable envelope: the area of a lot where you're actually allowed to put a structure, after subtracting the required clearances on every side.

Setbacks matter enormously for ADUs because a backyard or side-yard unit has to fit within them. A generous lot with tight setbacks can have surprisingly little usable space, while a modest lot with relaxed rear-yard setbacks may accommodate a detached unit comfortably. Recognizing this, many ADU-friendly laws reduce setback requirements for accessory units — for example, allowing a small rear and side-yard setback — precisely so that more lots can host one. Conversions of existing structures often benefit from these reduced standards as well.

Where a project can't meet a required setback, the owner may need to seek a variance or redesign to fit the buildable envelope. Setbacks interact with other zoning limits like height caps and floor area ratio to shape what's possible on a given parcel, so they're one of the first things to check before designing. Because the exact distances, how they're measured, and any ADU-specific reductions vary by jurisdiction and change over time, treat this as a general overview and confirm your lot's current setback requirements with the local planning department before you design.