Lot coverage and floor-area ratio (FAR), explained
Lot coverage limits the share of the lot that buildings may cover, seen from above. Floor-area ratio (FAR) limits the total floor area on all stories, as a multiple of the lot area. The largest building a district allows is the smallest of what the setbacks, coverage, floor-area ratio and height leave.
Updated . General information, not legal advice: the city’s code and its planning staff decide for your lot.
Lot coverage
Lot coverage is the building footprint divided by the lot area. A 40% limit on a 7,500 sq ft lot allows 3,000 sq ft of footprint. The code defines what counts: usually every roofed building, garages and sheds included, and often not uncovered decks, patios or eaves up to a set depth. Some cities also cap impervious cover, roofs plus driveways, patios and other hard surfaces, separately from building coverage.
Floor-area ratio
Floor-area ratio is the total floor area divided by the lot area. A ratio of 0.5 on a 7,500 sq ft lot allows 3,750 sq ft of floor area: one story of 3,750 sq ft, two of 1,875, or a larger ground floor under a smaller upper one. The code defines which floor area counts; garages, basements and low attics are often partly or wholly left out.
Many single-family districts set no floor-area ratio and rely on setbacks, coverage and height. Some cities use one to limit house size in older neighborhoods.
How the limits combine
Example
A 50 × 150 ft lot (7,500 sq ft): 25 ft front, 5 ft side and 10 ft rear setbacks, 40% coverage, a floor-area ratio of 0.5 and two stories:
Common mistakes
- Treating the envelope as buildable area: the envelope is the outer limit after the setbacks; coverage and floor area usually allow less.
- Reading living area as footprint: the county record’s living area counts heated floor area on all stories, the footprint only what the building covers on the ground. A two-story house can have twice as much living area as footprint.
- Forgetting what already stands: a garage or shed you keep already uses coverage.
- Trusting a mapped area: the lot area on a map and the area in the deed can differ. A permit application usually needs a survey, and the city works from that.
How the Lot Report shows it
The Lot Report computes the zoning envelope, the coverage cap and the floor-area cap from the lot’s mapped outline and the district’s rules, and shows the largest building with its sum (footprint × stories, or the ratio × the lot). Where no source gives a floor-area ratio, it says the ratio is not known and lets it cap nothing, instead of assuming a generic one.
Questions
Does a garage count toward lot coverage?
Usually yes, attached or detached, because it is a roofed building. Uncovered decks and patios usually do not, though they may count toward an impervious cover limit.
Does a basement count toward floor-area ratio?
It depends on the code. Many leave out floor area below grade, or count a basement only when it rises well above the ground.
If my district sets no floor-area ratio, is floor area unlimited?
No. The setbacks, the coverage cap and the height limit still apply: the coverage cap times the number of stories the height allows is usually the real limit.
Look up your own address
Enter an address: the Lot Report gathers the county record, the house’s condition, home values, schools, walkability, flood risk and the zoning rules, and draws the largest building they allow.
Find your lotMore guides
- What can I build on my lot?
Find your lot’s zoning district, read its setbacks, height and coverage limits, and work out the largest building allowed. A worked example and what to confirm with the city.
- What are setbacks? Front, side and rear yards explained
Setbacks are the distances a building must keep from the property lines. How they are measured, typical values, what may stand in them, and what else can push a building back.
- Can I build an ADU on my lot?
Whether a backyard cottage, garage apartment or in-law unit is allowed depends on state law, the city’s ADU rules and room on the lot. How to check each, with California, Washington and Texas.