Potential barriers and limitations of skyrise greenery retrofit in Singapore's public housing sector

As about 40-50% of the urban impermeable surfaces are unused rooftop, green roofs retrofitting on existing building stock can greatly increase the adaptive capacity of the cities. HDB, the public housing projects in Singapore that housed over 80% of its residential population, have immense potential for green roof retrofitting. However, the current achievement for integrating green roof is not significant in HDB compared to commercial and private residential sector. By exploring case studies from local projects and international policy instruments, three major barriers are identified: a. Lack of competitive against solar Photovoltaic (PV) system; b. Focusing on amenity and public utilization instead of improving building performance; c. Lack of supportive policy instrument from different level of government and sectors. It’s recommended to further investigate the feasibility of PV-green roof as a combined system that would benefit both skyrise greenery and renewable energy. Introducing formal retrofit scheme and revising green building rating tools would help to promote skyrise greenery in building retrofit. By shifting from amenity focus to performance based approach, skyrise greenery with primary concern on UHI reduction, water retention or energy conservation would be better for optimizing performance. Reframe stormwater management to decentralized approach and introduce indirect incentive to support skyrise greenery would be helpful, according to the successful cases in Berlin and Portland. Coordination and integration at different level of government agencies and sectors is a must to achieve the overall success in skyrise greenery retrofit in HDB buildings