Lot Coverage

Lot coverage is a zoning limit on how much of a lot a building's footprint may cover. It is usually expressed as a percentage — for example, a 40% lot-coverage limit on a 5,000-square-foot lot would generally cap the combined building footprint at about 2,000 square feet. Unlike floor area ratio, which counts total floor area across all stories, lot coverage measures only the ground-level footprint, so a two-story building and a one-story building of the same footprint use the same coverage.

Lot coverage matters for ADU and accessory-structure projects because adding a building adds footprint. On a lot already near its coverage limit, there may be little room for a detached unit without exceeding the cap — which is one reason a two-story design, or converting existing enclosed space, is sometimes the only way to add a unit. Many ADU-friendly laws ease coverage or related limits for accessory units so that more lots can host one.

Lot coverage works together with other dimensional controls to define the buildable envelope: setbacks fix where you can build, height limits cap how tall, floor area ratio caps total floor area, and lot coverage caps the ground footprint. A project has to satisfy all of them at once. What counts toward coverage — whether eaves, porches, decks, or detached structures are included — differs between codes, which can change the math significantly.

Because the allowed percentage, the way it is measured, and any ADU exemptions vary by jurisdiction and change over time, treat this as a general overview and confirm your parcel's current lot-coverage standards with the local planning department before designing.