退缩线与可建面积计算器 — 公式

Setback & Buildable Area

Setbacks are the minimum required distances between a building and the property lines. They create the "buildable envelope" that constrains where a structure can be placed on a lot.

Setback Types

  • Front setback: Distance from the front property line (street-facing), typically 15-30 ft
  • Rear setback: Distance from the rear property line, typically 15-25 ft
  • Side setback: Distance from each side property line, typically 5-15 ft
  • Corner lots: May have two front setbacks

    • Calculating the Buildable Envelope

    Buildable Width = Lot Width - (Side Setback x 2) Buildable Depth = Lot Depth - Front Setback - Rear Setback Buildable Area = Buildable Width x Buildable Depth

    Additional Constraints

    Setbacks define the maximum footprint, but the actual building may be smaller due to:

  • Lot coverage limits
  • Floor area ratio (FAR) limits
  • Parking requirements
  • Building height restrictions

    • 计算示例

    75 x 120 ft lot with 25 ft front setback, 20 ft rear setback, 8 ft side setbacks, planning a 2-story home.

    1. Total lot area: 75 x 120 = 9,000 sq ft
    2. Buildable width: 75 - (8 x 2) = 59 ft
    3. Buildable depth: 120 - 25 - 20 = 75 ft
    4. Buildable area: 59 x 75 = 4,425 sq ft
    5. Buildable as % of lot: 4,425 / 9,000 = 49.2%
    6. Max floor area (2 stories): 4,425 x 2 = 8,850 sq ft