Since 2000, the City of Tokyo has been taking measures to mitigate the impacts of the urban heat island effect, including covering roofs and walls with greenery in order to lower the surface temperature of buildings. To further these efforts, the Tokyo Metropolitan Government passed the Nature Conservation Ordinance in 2001xxxix, requiring the greening of building roofs and walls in addition to ground-level greenings for all new construction and existing buildings undergoing renovations.


The building sector is heeding local government’s requirements to implement green roofs. Thanks to the Ordinance, more than 5,700 new or existing buildings have added about 180 hectares (1,800,000 m2) of green roofs. Promoting the greening of existing buildings has proven to be an effective measure to counter the heat island effect. Research done in 2004 showed that new light-weight green roofs applied to existing buildings could lower the surface temperature by 25 degrees Celsius and ceiling temperature by 1 to 3 degrees Celsius even under thermal insulation.

Reasons for success

In this case, strong regulatory authority that enabled a mandatory requirement to implement green roofs was heeded by the building sector. The Tokyo Metropolitan Government also did media outreach and advertised the Conservation Ordinance and compliance requirements widely.

When/why a city might adopt an approach like this

This type of approach works best when a city has strong legislative authority and enforcement over the building sector. Apart from that, having a strong regulatory authority to ensure adoption of the regulation – and if necessary enforcement of the regulation – Is crucial to the success of similar measures.

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  • Environmental
  • Social
Key Impact
More than 5,700 new or existing buildings have added about 180 hectares (1,800,000 m2) of green roofs
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