The design approach was to create a simple, two-storey unit that would fit into a mature neighbourhood. After you have taken off your shoes in the entrance area essential to any Japanese house, a spacious staircase leads up to a living-dining area on the first floor, which is designed open plan in order to make the best use of daylight. The well-positioned windows frame nice views over the river and the hills of Kamakura.
The site does not have enough private open space at the ground-floor level. To overcome this problem, the architects designed an access from the dining space to a roof garden. The building itself had to be constructed within a very limited budget due to the high purchase price of the site (approx.2,500 Euro/m²). The house was built using the Canadian 2/6-inch timber-frame construction method and insulated with wood-fibre insulation.
The wood-aluminum composite windows with triple glazing were shipped over from Germany, as windows with such high energy performance are not yet produced in Japan. To match the surrounding environment, charcoaled cedar panelling was chosen as the external wall finish. This is a very traditional construction material in Japan, because it is known to be highly durable against moisture and insects, an issue relevant to the local climate.
There is currently no minimum energy-efficiency requirement for new residential buildings in Japan; a house with singleglazed windows and no insulation is still acceptable.
KEY ARCHITECTS tried to find a comfortable balance between summer and winter by applying the Passive House principle.
In such a humid sub-tropical climate, reducing the dehumidification and cooling demand during summer is more difficult than reducing the heating demand in winter. Another conflicting issue involved the strict earth quake requirements for Japan, which require rigid load-bearing walls instead of diffusion-open walls that prevent condensation within the external walls during both summer and winter months.
Project information: Certified detached house
New construction | Kamakura Kanagawa, Japan
Living area (Treated floor area) according to PHPP: 78 m²
Year of construction: 2009
Architects: KEY ARCHITECTS, Japan
Photographs: KEY ARCHITECTS, Japan
External wall: plasterboard | battens with service cavity | moisture-adaptive vapour barrier | stud frame with wood-fibre insulation 140 mm | timber board | wood-fibre insulation 100 mm | permeable membrane | ventilated rain screen
Roof: plasterboard | battens with service cavity | moisture adaptive vapour barrier studs with wood-fibre insulation 290 mm | timber board | stud frame with wood-fibre insulation 100 mm
Floor slab: XPS insulation 100 mm | concrete | screed | timber floor finish
External wall: U = 0.16 W/(m²K)
Roof: U = 0.10 W/(m²K)
Floor slab: U = 0.22 W/(m²K)
Thermally insulated wood aluminium composite windows, triple glazing with low-e coating and Argon filling Uw,installed = 0.85 W/(m²K) Ug = 0.64 W/(m²K) | g-value = 51%
Ventilation: supply and exhaust air with counter-flow heat exchanger | summer bypass | heat pump for heating, cooling / dehumidification and domestic hot water provision | heat distribution using air-conditioners
Airtightness of building n50 = 0.14/h
Heating demand (calculated according to PHPP) 15 kWh/(m²a)
Cooling demand (calculated according to PHPP) 15 kWh/(m²a)
Primary energy demand (calculated according to PHPP incl. the total electricity demand) 113 kWh/(m²a)