The initial design of the house included a heat retaining wall. The purpose of this wall is similar to a Trombe wall which is to absorb solar energy coming through a window during the day and to radiate it back into the house at night. The wall separates the kitchen from the living room and faces the three big bay windows in the living room. The effectiveness of a Trombe wall or heat retaining wall relies on the material being dense and good at accumulating heat. Bricks, mortar made of soil and sand, and stones are all good examples of heat absorbing materials. We chose stones as we have plenty of them close to the construction site and thought it would be nice to have some visible stones inside the house.