Climate Zone 4A covers the Mid-Atlantic and parts of the Southeast including NYC, Philadelphia, DC, Richmond, Nashville, Raleigh. Climate characteristics: hot humid summers (design cooling 91-95F), cold winters (design heating 10-20F), 3500-5500 HDD65, 1000-2000 CDD65. Insulation requirements (IECC 2024 residential): wall R-20 or 13+5ci, ceiling R-49, floor R-19, basement wall R-10ci, slab R-10 perimeter. Window maximum U-0.30, SHGC 0.40. Air barrier: max 3 ACH50. Concrete considerations: 45-60 freeze-thaw cycles per year, air entrainment required for exposed concrete, frost depth 24-36 inches (foundation depth). Seismic: Design Category B (NYC) to C (parts of VA/NC). Wind: 110-130 mph basic wind speed. Rainy season: spring/fall. Primary scheduling impacts: concrete work limited Dec-Feb without cold weather protection, exterior painting Apr-Oct.