Setback, Lot Coverage & Buildable Area Calculator

How it works

Envelope = (width − 2 × side) × (depth − front − rear); max footprint = min(envelope, lot × coverage %); impervious = footprint + paving ≤ lot × impervious %

Three layers of zoning control how much of a lot a house can occupy. Setbacks push the building away from each property line, leaving a buildable envelope in the middle; lot coverage caps the share of the lot under roofs regardless of where they sit; and impervious-surface limits — increasingly common for stormwater reasons — add driveways, patios and pool decks to the count. The binding constraint differs by lot: on narrow deep lots the side setbacks govern, on small lots coverage does, and on lots with long driveways the impervious cap is the surprise. Codes also carve exceptions (eave projections, open porches, detached sheds under a size) and overlay rules such as corner-lot sight triangles or height planes, so the envelope here is the starting point for a site plan, not the final word.

Worked example

A 60 × 120 ft lot (7,200 ft²) with 25/20 ft front/rear and 7.5 ft side setbacks leaves a 45 × 75 ft envelope of 3,375 ft²; 35% coverage allows only 2,520 ft², so coverage governs. A 2,200 ft² footprint complies (30.6%), but with 900 ft² of paving the impervious total is 3,100 ft² — 43%, inside the 50% cap with 500 ft² to spare — and two storeys on the maximum footprint would give about 5,040 ft² gross.

Frequently asked questions