Hutong 3.0: Beijing family of 6 enjoys clean indoor air in their 45 sqm hutong home! The courtyard is located just a stone throw away form Tiananmen in the Dashilar district of Beijing. On a footprint of 45 sqm the refurbished north house of the yard accommodates three generations. Apart from the challenge of having to house this many people within a rather small area while providing them with a comfortable living space we set out to create a well performing building envelope. To avoid the inherent problems of deteriorated hutong houses such as notoriously damp floors and walls a ‘House in House’ concept was developed for the refurbishment. Apart from re-designing the house, we had promised the owners one of the most essential needs in Beijing: clean indoor air! The new house has been executed with a rather air tight envelope while the energy recovery ventilation system ensures a comfortable room climate and a controlled flow of clean air do to the integrated PM 2.5 filters. Besides the 4 bedrooms the small dwelling offers a living room, dining room, mezzanine reading room, kitchen and bathroom. 2 new skylights provide additional daylight.