Green Roof Embodied Energy

The potential energy savings of green roofs should be balanced against the added embodied energy required for their construction.

Green roof embodied energy.

Highlights a green roof thermal model was coupled to a building simulation code. The impact of a green roof on the roof temperature and heat flux is studied. Both sod roofs and lwa based lightweight aggregates roofs have been found to have a negative impact on the quality of their resulting runoff. Because they are fired they can have an embodied energy of around 6 5 mj kg university of bath uk see wikipedia on embodied energy.

On first thoughts a living roof be it turf or sedum might seem to have less embodied energy than say a clay tile. Green building research is being done by national laboratories private companies universities and industry. In australia the energy benefits of green roofs are most pronounced in their ability to reduce summer cooling demands. Assuming a generic industry root barrier drainage layer and 6 0 cm of substrate consisting of half sand and heat expanded slate by volume as was the case in the getter et al.

By comparison a cool roof on this building will save about 700 btus per square foot per year. The next largest category of research is materials and resources. According to a usgbc report published in 2006 over 70 percent of the green building research is focused on energy and atmosphere research. There can be occasional surprises.

2009b study total embodied energy for the green roof components are 23 6 kg co 2 per square meter of green roof. Though the embodied energy is high there are few toxicity issues involved in the manufacture of clay tiles. Green roofs reduce building energy demand and improve thermal comfort. Concrete has a lower embodied energy but greater toxicity in its emissions.

Our one square foot patch of green roof will save about 1 000 btus per year in cooling energy which means that it will take about 40 years to recover the process embodied energy of the green roof. This value is equivalent to 6448 g c m 2 which is significantly greater than 378 g c m 2. While this is lower than steel sheet products like concrete tiles clay tiles high mass per unit area comes into play so clay tiles will have a higher embodied energy per total roof area than sheet products. The effects of the leaf area index the roof insulation and the climate are discussed.

Some of the traditional ways of house building are extremely low in embodied energy. An example is cob using the earth available locally and mixing it with straw of which there are about 70 000 examples mainly in the south west of england. The embodied energy for green roof components are 23 6 kg m 2 5 pounds per square foot co 2 of green roof. Green roofs provide significant thermal insulation and shading for a building.