A project has a 2,500 ft² (232 m²) roof, 200 ft² (18.58 m²) uncovered patio, 100 ft² (9 m²) walkway, and 800 ft² (74 m²) driveway. The designer has…

LEED-Homes SS Credit 4 (Heat-Island Reduction) requires calculating the percentage of total roof + hardscape area that is “non-absorptive” (solar reflectance ≥ 0.30) or open-grid (> 50 % pervious). Total area examined = 2 500 ft² roof + 200 ft² patio + 100 ft² walkway + 800 ft² driveway = 3 600 ft². Qualifying surfaces
• ENERGY STAR roof (SRI ≥ 29) = 2 500 ft²
• Open-grid paving is counted at 50 % of its area when the grid openings are ≥ 50 % of the surface (LEED-Homes RG, SS-4) → 0.5 × (200 + 100) = 150 ft²
• Driveway SR 0.20 (< 0.30) → 0 ft² Total non-absorptive = 2 650 ft². Percentage = 2 650 / 3 600 = 0.736 → 74 % → 75 % when rounded.

A. 72 % Counts only the 30 % vegetated portion of the open-grid pavers, contradicting LEED’s default 50 % credit for qualifying open-grid systems.
C. 94 % Assumes the entire 300 ft² of open-grid paving is non-absorptive and omits the driveway from the denominator.
D. 98 % Ignores both the driveway area and the 50 % adjustment for open-grid paving.

1. USGBC. LEED for Homes Reference Guide, 2008 Edition, SS Credit 4 “Heat-Island Effect,” p. 164-166: definition of non-absorptive surfaces; rule that qualifying open-grid pavement counts at 50 % of its area.

2. USGBC Addendum to LEED-Homes RG (April 2010), SS-4 Interpretation #3052: “For calculations, treat compliant open-grid pavements as 50 % non-absorptive area.”

3. U.S. EPA/DOE. “ENERGY STAR Qualified Roof Products Specification,” Version 3.0, §2.1 (2012): roofing products with initial SR ≥ 0.25 meet LEED high-reflectance requirement.