Japans first passive house.

 
I decided that I wanted to do something a bit different for this blog post and thought that Asia would be an interesting case study for a passive house development. I chose the first ever Passive house built in Japan.

The house was built in Japan in 2009. Planned by local practice Key Architects, the first certified Passive House in Japan has been built in the city of Kamagura, Kamakura, approximately 50km southwest of Tokyo. The two-storey wooden building can be considered a prototype for the application of the German building standard even in humid, subtropical climates.

It was originally not the intention of this project to get the Passive House certification. The idea evolved from Miwa Mori’s (the owner of Key Architects) experience with developing a social housing prototype with Passive House standard for Ireland while working for MosArt Ltd. in Wicklow. The absolute must requirement by the client was that the house be driven solely by electricity, as the house mortgage was provided by the owner’s employer, the Tokyo Electric Power Company.

The design approach was to create a simple, two storey unit which would fit into a mature neighbourhood. Upon entering the house, a staircase with a double height space leads up to an open plan living-dining area at the first floor level, in order to access the space with the most daylight. 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 site purchase price (ca. 2500euro/sqm).

In such a humid sub-tropical climate, reducing dehumidification and cooling demand during summer is more difficult than reducing heating demand in winter. Another competing issue was the strict earth quake requirements for Japan which require a rigid load bearing wall versus a diffusion open wall, in order to avoid condensation within the external walls during both summer and winter months. This building project was treated as a pilot project by the Passive House Institute in Darmstadt, Germany and the house will help improve the Passive House calculation methods for warmer regions.

This home is a great example of the Passive House standards building techniques - it features triple-pane windows, thick walls for insulation, and a minimum of exterior joints, which are prone to air leaks and thermal bridging. The core of the HVAC system is a HRV - or Heat Recovery Unit. This passive house has an energy profile a ¼ of what is considered the average kwh/sq ft.

This ultra-efficient house is a far cry from traditional Japanese housing, which use thin wall construction and single-pane windows, which even today is still quit typical. Japanese houses have a maximum life span of 30 years, at which point they are knocked down and rebuilt.

There is currently no minimum energy efficiency requirement for new residential buildings in Japan where one million new houses are built every year. A house with single glazed windows and no insulation is still acceptable.

Personally I find this project very interesting and am looking forward to the passive house concept expanding to more countries. I like the link between the architect and Ireland and the construction details are not too dissimilar to what I have constructed for our passive house project.

The Passive House standard is becoming an important measure of sustainable building, and in Japan’s climate these homes would save an enormous amount of energy.


Construction Details.

Timber construction, 78 m²

Exterior wall:

15 mm plasterboard and render finish
24 mm service cavity
140 mm wood fibre insulation
13 mm wood board (earthquake resistant)
12 mm wood board (fire proof)
100 mm wood fibre insulation
11 mm rain screen, Cedar panel

U-value = 0,16 W/(m²K)

For a very good thermal protection in passive houses the U-value for all exterior building elements in Central European Climate is recommended to be less than 0,15 W/(m²K).

Floor slab:

11 mm wood floor finish
165 mm reinforced concrete floor
155 mm XPS insulation

U-value = 0,217 W/(m²K)

For a very good thermal protection in passive houses the U-value for all exterior building elements in Central European Climate is recommended to be less than 0,15 W/(m²K).

Roof:

15 mm plasterboard and render finish
100 mm service cavity
286 mm wood fibre insulation
37 mm wood board
75 mm wood fibre insulation
Metal roofing system with timber deck.

U-value = 0,101 W/(m²K)

Glazing: 

Triple Argon double low-e
Ug-value = 0,64 W/(m²K)
g-value = 51 %

Air tightness:

n50 = 0,14/h which is well below the 0.6 needed.

Annual heating demand:15 kWh/(m²a) calculated according to PHPP

Heating load:18 W/(m²) calculated according to PHPP

Primary energy requirement:113 kWh/(m²a) total demand on heating installation, domestic hot water, household electricity and auxiliary electricity calculated according to PHPP.




The following video is an interesting interview from the 15th International Passive House Conference Innsbruck, Austria, May 2011. It contains interviews with Wolfgang Feist (PHI), Ann-Marie Fallon (Ireland), Bjorn Kierulf (Slovakia), Miwa Mori (Japan). Miwa Mori talks about the first passive house in Japan.