IECC CZ 7 (very cold): Fairbanks, northern Alaska, northern Minnesota/Wisconsin, mountain regions. HDD: >9000. Design temp: -40F to -60F. Residential envelope: ceiling R-49, wall R-20+10ci or R-13+15ci, floor R-38, windows U-0.28 (triple pane required). Air leakage: 3 ACH50 (Passive House recommended). Frost depth: 6-12+ ft. Permafrost: pile foundations, thermosyphons to keep ground frozen. Key: ice dam prevention (air sealing + ventilation), extreme snow loads (50-100+ psf), short construction season, material logistics, permafrost stability. HVAC: heating-dominated, ground-source heat pump if available, HRV/ERV essential.