The built environment contributes around half of all greenhouse gas emissions and 87% of residential buildings the UK will have in 2050 are already built (Kelly, 2009), there is a need to adopt sustainable retrofit for existing residential buildings. Furthermore these statistics are broadly similar across many countries. The question is; what are viable solutions? One answer may be to retrofit with green roofs as there are environmental, economic and social benefits. Environmental benefits

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... de potential reductions in operational carbon emissions, reductions in the urban heat island, increases in biodiversity, housing temperature attenuation and reductions in stormwater run-off. Economically, benefits are reduced roof maintenance costs and lower running costs. The social gain is the creation of spaces where people have greater access to nature. However there are barriers to the adoption of retrofitted green roofs; which include perceptions of structural adequacy, risk of water damage, high installation and maintenance cost, as well as access and security issues. In some locations the intent will be to reduce cooling loads, whereas others will desire thermal insulation, or will seek reduction in stormwater run-off. The ability to meet the demands will depend on budget and physical characteristics. Many Australian and Brazilian residential buildings have profiled metal sheet roofing which is a lightweight material with poor thermal performance During summer periods Sydney as well as Rio de Janeiro temperatures can reach 45 degrees Celsius and rainfall patterns are variable and changing. This research reports on an experiment on two small scale profiled metal sheet roofs in both cities which aimed to assess thermal performance. One roof was planted to compare performance to an unplanted roof. The findings are that considerable variation in temperature were found in both countries indicating that green roof retrofit could lower cooling energy demand considerably.