Calculateur de Ratio d'Emprise au Sol — Formule

Lot Coverage Ratio

Lot coverage measures how much of a parcel is covered by buildings and impervious surfaces. Zoning codes use coverage limits to control density, manage stormwater, and preserve neighborhood character.

Building Coverage Ratio

Building Coverage = Building Footprint / Lot Area x 100

This measures only the building footprint (first floor area), not total floor area.

Impervious Coverage Ratio

Impervious Coverage = Total Impervious Surfaces / Lot Area x 100

Includes buildings, driveways, patios, walkways, and any surface that prevents water absorption.

Why Coverage Matters

  • Zoning compliance: Most zones cap building coverage at 25-50% and impervious at 50-75%
  • Stormwater management: Higher impervious coverage increases runoff and may require detention facilities
  • Neighborhood character: Coverage limits prevent oversized buildings on small lots
  • Permitting: Exceeding coverage limits requires a variance, which is not guaranteed

    • Exemple Résolu

    10,000 sq ft lot, 2,500 sq ft building footprint, 800 sq ft driveway/patio, 200 sq ft other impervious, 35% max building coverage, 60% max impervious.

    1. Building coverage: 2,500 / 10,000 = 25.0%
    2. Total impervious: 2,500 + 800 + 200 = 3,500 sq ft
    3. Impervious coverage: 3,500 / 10,000 = 35.0%
    4. Remaining building capacity: 3,500 - 2,500 = 1,000 sq ft
    5. Remaining impervious: 6,000 - 3,500 = 2,500 sq ft
    6. Open space: 10,000 - 3,500 = 6,500 sq ft (65.0%)