First prize winner in the Passive House Lozen competition organised by Passive House Bulgaria in 2012.For the design of the Lozen Passive House we have studied different options for situation and form of the building. Starting from a narrow single-storey house with all rooms facing south for maximum solar gains, through an open plan narrow house with long east and west facades for best natural ventilation, we have come to the nearly cubical shape of a two-and-a-half storey semi-sunken into the ground building. During the design process, a dynamic computer modeling and simulation has been undertaken involving Ecotech for sight insolation modeling, Radiance for interior daylighting and illuminance modeling and IES VEfor energy modeling and computational fluid dynamics. Design by: Architecture - dontdiy – arch.Hristo Stankushev and arch.Svetoslav MichevMEP and Sustainability Consultant - AEE Asian European Engineering Ltd. - eng.Rumen Yordanov