Lot coverage
The share of a lot covered by buildings or other structures, expressed as a percentage. It limits a building's footprint rather than its total floor area.
What it means
Lot coverage is the percentage of a lot's area occupied by structures. A 40 percent limit on a 10,000-square-foot lot permits a 4,000-square-foot footprint.
The critical question in any ordinance is what counts as coverage. Cities vary on whether to include detached garages, covered patios, decks above a certain height, or pools. Some codes distinguish building coverage from a broader impervious surface limit that also counts driveways, walkways, and parking areas — driven by stormwater management rather than building bulk.
Coverage works alongside setbacks and FAR. Setbacks say where you can build, coverage says how much of the ground you may occupy, and FAR caps the total floor area across all stories.
Why it matters
Coverage is what preserves open ground on a lot — for drainage, landscaping, and the spacing between buildings that gives a neighborhood its character. It is often the standard that decides whether an addition to an existing house is possible at all.
For larger sites, an impervious surface limit frequently binds before the building coverage limit does, because parking and drives add up quickly. That surprises teams that only checked the building number.
An example
A homeowner on a 7,500-square-foot lot in a district capped at 35 percent coverage may cover 2,625 square feet. The existing house is 2,100. A proposed 400-square-foot addition brings it to 2,500 and still fits. Adding a 300-square-foot detached garage would reach 2,800 and exceed the limit — assuming the ordinance counts detached accessory structures toward coverage, which is exactly the sentence to go read.
How Conflation Labs fits in
Our Site Plan Review Agent computes coverage from a submitted site plan and checks it against the applicable limit, using the city's own definition of what counts, with a citation to the section it applied.
Where this comes up in our work
Common questions
Usually not toward building coverage, but often toward a separate impervious surface limit. Many ordinances carry both numbers, and a site can pass the building test while failing the impervious one.
The same way — footprint area divided by total lot area — but the lot area itself needs care. Some ordinances exclude submerged land, easements, or the portion of a lot within a street right-of-way from the calculation, which changes the denominator and therefore the result.