Deep retrofit of a 1925 wood-frame single-family house in Altadena, CA (climate zone 5), pre-certified to EnerPHit step-by-step standard. The project combines envelope upgrades and full electrification. A balanced mechanical ventilation system with heat recovery (~83% efficiency) ensures IAQ and comfort. Heating, cooling and DHW are provided by high-efficiency heat pumps. The strategy enables step-by-step implementation aligned with maintenance cycles while achieving ~90% heating demand reduction (from ~56 to ~6 kBTU/ft²·yr). The design prioritizes resilience, indoor air quality, and reduced operational carbon.
