From Shelter to Guesthouse: A Longitudinal Case Study on User-Driven Incremental Growth and Environmental Performance in a Modular Timber Dwelling, Türkiye

Despite timber’s strategic role in the circular economy, its application in Türkiye remains negligible compared to the rigid reinforced concrete (RC) housing stock, which limits flexibility and penalizes the environment. This study investigates the adaptability and environmental performance of modular timber construction via a 17-year longitudinal case study in Seferihisar, İzmir. Using architectural observation, user interviews, 3D BIM, and a comparative LCA, findings reveal the structure successfully accommodated a six-phase functional transformation—the structure’s gross floor area increased by 6.19 times more (from 21 m 2 to 151 m 2 ) and bed capacity from 2 to 18—with virtually zero demolition waste through dry-assembly techniques. Crucially, normalized LCA proves timber’s ecological superiority: achieving an embodied energy intensity of 6.60 GJ/m 2 (1.2 times less than the RC equivalent’s 7.97 GJ/m 2 ). Furthermore, biogenic carbon storage enabled the timber dwelling to reach a negative Global Warming Potential (GWP) of −26,118.39 kgCO 2 (a carbon sink), whereas the RC model emitted +39,081.22 kgCO 2 . Given that secondary housing predominantly comprises two-story structures, lightweight timber sustainably meets this typological demand. Ultimately, user-driven modular timber presents a resilient, eco-efficient, circular economy model for second-home and post-disaster settlements.