What is the problem?

Most of the roofs in the world’s cities and built-up environments are dark in colour and consist of nothing other than building materials. They are totally exposed to the weather. On cold days roofs are cold, on hot days roofs can get extra hot, reaching temperatures up to 30°C hotter than the air. This additional warming contributes to an effect known as the Urban Island Effect, where it is significantly hotter in cities then out.

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Traditional roofing makes the contrast between the outside and the inside temperatures stark, meaning it takes a lot of energy to cool and warm a building. More energy means more GHG emissions.

What might help?

Planting vegetation on roofs would have the following effects.

• Provide an insulating layer, keeping buildings cooler in hot weather, and hotter in cold weather. This would lower the amount of energy required to regulate the building temperate, lowering GHG emissions and energy cost.
• Cools the outside air temperature and combat the Urban Island Effect.

In short, having lots of vegetation on roofs will reduce GHG emissions and make urban areas a cooler, more pleasant place to live.

How feasible is it?

Green roofs can come at a cost as the extra weight of plants, soil and water requires stronger, reinforced roofs. It has been estimated that this cost will be more than the savings from energy – 13% adoption of green roofs by 2050 would cost 815 billion US$[1].

Are there any other benefits?

• Plants and soil would capture rainwater and help protect cities against flooding during periods of heavy rainfall.  
• A huge positive biodiversity impact through providing habitats for wildlife.
• Using roofs for urban farming can increase food security.
• An abundance of green space and vegetation encourages vibrant, healthy, and productive lifestyles.
• Reduce the impact of urban air pollution.

What can be done?

Creating incentives for construction companies to build or retrofit green roofs will principally come from building and urban planning policies. Therefore, the most impactful thing an individual can do is to write to their local pollical representative and show support / demand for green roofs.