Green Light for ‘Passive Home’

by Alana Bonzi
wifm_winter10_low-48Kamakura gets Japan’s first certified eco-house

So-called passive homes can be retrofitted with existing technology to reduce their effect on greenhouse gases (GHG). But in Japan’s residential market, it can make more economic sense to build a passive home from scratch. Miwa Mori, of Key Architects, and her team have designed and built Japan’s first certified passive home in Kamakura.

A passive home has low impact on the environment — with solar panels, insulation, double-glazing and energy-eff i c i e n t appliances — and the goal is to produce a zero-carbon home.

Architecture 2030, a U.S. NGO led by architect Edward Mazria, was the first to bring the building industry into the GHG. “U.S. Energy Information Administration illustrates that buildings are responsible for 48% of all energy consumption and GHG emissions annually; globally the percentage is even greater. Seventy-six percent of all power plantgenerated electricity is used just to operate buildings. Clearly, immediate action in the building sector is essential if we are to avoid hazardous climate change,” the NGO states on its website.

wifm_winter10_low-49The Passive House Institute in Germany issues certification. Indeed, the Germans have led this field and the EU has passed legislation to encourage the industry. For a home to be passive the technology and construction must be affordable and there should be enough comfortable living space.

“Improved thermal wraps could enable space heating via simple utilities such as the ventilation system,” says Mori.

However, there were special challenges for Japan’s first passive home: an anti-seismic structure; insulation to resist extreme summer humidity; termite resistance; electric-only power, and the creating of an open space.

Miwa and her team finished the project in August 2009 at a cost of just ¥21 million. On a 118.76-m2 site in Kamakura, they created a 93.06m2 family home in three months—made of a two-story timber frame, with heating and cooling requirements of 15kW/m2, and energy consumption of 120Wh/m2.

wifm_winter10_low-51“An eco-house is not full of technical gadgets, but it is a balance of active and passive technology.” Mori recommends we “look at the total energy consumption of the house against each device.”

As the Japanese housing market lacks an eco-house standard, Miwa advises that consumers employ third-party assessment and certification. Miwa warns there is danger in using oil-based materials instead of environmental ones. “Encouraging builders and consumers to chose more ecological and local construction materials is one way forward.”