Reduction Of Heat Flux Green Roof

Green roofs can reduce the flow of stormwater from a roof by up to 65 and delay the flow rate by up to three hours.

Reduction of heat flux green roof.

The effect that the green roof media has on the thermal performance of the roof system was evaluated. Green roofs reduce the heat flux through the roof and less energy for cooling or heating can lead to significant cost savings. The average 24 h effect of sedum covered green roof was a 0 2 c increase of air temperature 15 cm above the ground. The best net heat flux gains for vegetated green roofs were 4 7 w m 2 for the sand roof and 7 8 w m 2 for the silt clay roof.

Research by david sailor at portland state university also concluded that low latent heat flux due to lack of vegetation in urban areas is the most significant contributing factor to the uhi phenomenon. The allegheny county office building green roof was found to lose 8 2 less heat than the control roof in heating months and gain 75. Also under the described laboratory conditions the uninsulated green roof samples with plants showed an average heat flux reduction of 25 compared to samples without plants. Green roof temperatures can be 30 40 f lower than those of conventional roofs and can reduce city wide ambient temperatures by up to 5 f.

Green roofs with silt clay soil required more than twice the amount of soil moisture than green roofs with sand to achieve similar roof heat transfer rates. Peak membrane temperatures were reduced by the green roof and were delayed by 5 h relative to a traditional roof 11. In summer the green roof protects the building from direct solar heat. New york has recently approved a tax abatement of up to.

1 2 in addition green roofs can reduce building energy use by 0 7 compared to conventional roofs reducing peak electricity demand and leading to an annual savings of 0 23 per square foot of the roof s surface. In toronto researchers found that average daily heat flow through a green roof was reduced 70 90 in the summer and 10 30 in the winter relative to a traditional roof. Shading the outer surface of the building envelope has been shown to be more effective than internal insulation. The green roof caused a mean reduction of 4 96 c proving that green roofs contribute to reducing indoor room temperature and thermal lag promoted by the green cover where the heat input takes.

Green roofs reduce building energy use by cooling roofs and providing shading thermal mass and insulation. The hamerschlag hall green roof was found to lose 26 less heat than the control roof in heating months.