Our mission was to extend the living spaces close to the current detach residential unit to satisfy future needs of the family. There was a large area of lawn right behind the existing building that faces the desire sunlight from north. The aim was to put new mass in this part of the site homogeneously through highlighting simplistic characteristics of the existing building and its overall form. The new mass is consisted of two pitched roof volumes that is shaped the main living spaces and a straight corridor that connects persons to the northern garden among the sunlight that penetrates through skylights. The design ideas had been developed in two alternatives: A flat unit and a duplex one. In flat alternative, public and private areas had been separated by a straight corridor while the duplex alternative provides private areas in an independent floor. The old building transition to the new one is articulated by a swimming pool that is located between them. Visually and emotionally, there is ‘one’ residential building while the existing building and the new one have different architectural features: Sustainability and Abstraction. The new building captures the essence of the modern and minimal houses and follows the sustainability goals. The building materials including thermo wood, sandwich panels and wooden window frames, utilizing natural light and ventilation, interior garden and the stand alone photovoltaic system widely address the sustainable house design.