Prolonged winter power outages pose an increasing risk in heating-dominated regions undergoing electrification and decentralization of energy systems. This study investigates how building construction, renewable energy generation, distributed energy storage and reduced heated area influence the duration of maintaining acceptable indoor temperatures without active electrical heating. The analysis is based on experimentally derived cooling curves from two full-scale, geometrically identical single-family houses exposed to a 12-day cold period, differing in thermal mass and ground coupling. Thermal performance is evaluated using three temperature thresholds representing different levels of habitability: 18 °C (comfort), 15 °C (reduced habitability), and 12 °C (survival). The baseline case considers fully passive operation, followed by scenario modelling incorporating internal heat gains, on-site renewable energy input (solar and small-scale wind) and two storage configurations (20 kWh and 20 + 50 kWh). An additional strategy of reduced heated area, representing a minimum habitable zone, is introduced to assess its impact on extending thermal autonomy. The results show that construction type strongly affects the duration of passive thermal autonomy, with higher thermal mass and ground coupling significantly delaying long-term temperature decline. Renewable energy contributes to extending the duration above critical thresholds; however, its impact is constrained by variability and limited winter availability. Distributed storage further increases thermal autonomy, but its effectiveness depends on building characteristics and outage duration. Reducing the heated area markedly improves performance and can extend the duration of maintaining habitable temperatures to a similar extent as increasing storage capacity. The findings demonstrate that maximizing thermal autonomy during winter outages requires an integrated approach combining building design, renewable energy utilization, storage capacity and operational strategies. The results provide quantitative support for incorporating passive survivability and minimum energy demand criteria into residential energy planning under cold-climate blackout conditions.