Every site plan answers to two separate ceilings: the envelope left over once setbacks are subtracted, and the footprint your coverage percentage permits. Enter your dimensions to see both at once, along with how much you have left to add. What comes out is a planning sketch built from your numbers, not a survey.
Enter the lot dimensions and the setbacks your zoning district requires, in feet. The result is a planning envelope derived from what you type, not a boundary determination.
Nothing here is a quote, a bid, an engineering determination or a boundary determination. We are a drafting and design firm: we coordinate with a licensed structural engineer and a Licensed Land Surveyor when your project needs one, rather than performing or stamping that work ourselves.
The envelope is pure geometry. Subtract a side setback from each edge of the width, subtract the front and rear setbacks from the depth, and whatever rectangle survives is the ground a structure is allowed to occupy. Run that on a 60 by 100 parcel carrying 5-foot sides and 20-foot front and rear setbacks and you are left with 50 by 60, or 3,000 square feet of buildable ground.
Coverage is pure arithmetic. Your city fixes a share of the parcel that the footprint may not exceed, and across Bay Area residential districts that share usually sits somewhere between 35 and 50 percent. Apply 40 percent to a 6,000 square foot parcel and you get 2,400 square feet of footprint in total, counting whatever already stands there. Notice that the same lot just produced two different numbers. That is the entire point of running both: the smaller one is the one your design has to obey.
The expensive mistake is designing to the coverage figure and learning at plan check that the envelope will not accept the shape. A 900 square foot addition can satisfy the coverage math perfectly and still demand 55 feet of length where the envelope offers 50, and closing that gap is not a markup, it is a fresh design. Nailing both figures down before schematic design costs a few hours and routinely saves weeks.
Coverage is not defined the same way twice. Some cities tally covered porches, cantilevers, roof overhangs past a stated projection, detached sheds and covered patios; others exclude them. Some maintain a separate impervious-surface limit for stormwater that sweeps in driveways and flatwork the coverage rule ignores entirely. Floor area ratio is a third and independent ceiling. It governs total floor area summed over every story instead of the ground the building sits on, and once a project goes to two stories the FAR frequently binds long before either limit shown here does. Which definitions attach to your parcel is a question for your planning department, not for a calculator.
Recorded easements, creek and flood overlays, protected tree zones, daylight plane and upper-story step-back rules, and the width the fire department needs to get a truck through all shave further off what is genuinely buildable. A width-times-depth calculation shows none of them, and an aerial photo will not reveal them either. Locating them on a measured site plan is where most of the projects we draft actually begin, and that work falls under our site plans and property surveys scope, which builds existing-condition site plans from your recorded plat and parcel data. Where the project genuinely needs a boundary survey or an elevation certificate, that determination belongs to a Licensed Land Surveyor and we coordinate it separately instead of performing it. Those constraints then carry through the whole permit set so that the site plan, floor plans and elevations tell the plan checker one consistent story. We prepare the documents and coordinate an independently licensed engineer when structural design is required. We do not build, and no set of drawings can promise you an approval.
No. It is a planning sketch assembled entirely from figures you typed, and it locates nothing. There is no stamp on it, it is not a legal or recorded boundary, and it does not establish where a single property line falls. If you are not certain where your lines actually run, only a Licensed Land Surveyor can settle that, and we coordinate one for you. We draft site plans from recorded property data; land surveying is not what this firm does.
From the zoning district your parcel sits in, either in the municipal code or straight from the planning counter. Locate the parcel on the city zoning map, then work through the standards table belonging to whichever district it lands in. Borrowing a neighbor's numbers is a trap, because a district line can run mid-block and the standards on either side of it can differ. Corner lots, flag lots and overlay districts also routinely carry figures that depart from the base district.
Generally yes, though the definitions differ city by city. Certain jurisdictions exempt accessory structures under a stated size, others tally covered patios and porches, and others again maintain a parallel impervious-surface limit that catches driveways too. Confirm the local definition with your planning department rather than assuming something is excluded.
Because the state carved out an exception. An ADU generally keeps its side and rear setbacks at 4 ft whatever the underlying district asks for, which lets it sit nearer the line than an addition of identical size could. The front yard usually still answers to local zoning, and the carve-out does not sweep aside recorded easements or fire access requirements.
On the figures you entered, what already stands meets or passes the coverage allowance for the parcel, so any new ground-floor footprint would put you over. The usual responses are to build up instead of out, remove existing footprint, pursue a variance, or look at the ADU allowances, which in many cases are handled separately from ordinary coverage limits. Verify the coverage percentage itself before acting on that result, since an assumed figure changes the answer entirely.
It is enough to sanity-check an idea over a weekend. Real design begins from a measured site plan that puts the property lines, the easements, whatever already stands, the trees and the grades in their true positions. A plan checker reviews that drawing. A rectangle worked out from two dimensions does not stand in for it.
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