Vegetated roofs can have an enormous impact on the reduction of the "heat island effect". Studies have shown that if 20% of D.C.'s current buildings were retrofitted with extensive greenroofs the cities overall mean temperature could be lowered by 1-2 degrees if 50% of the buildings were "greened" the ambient temperatures may decrease by 6%. Vegetated roofs also provide a high level of noise mitigation and are a popular alternative for buildings located near airports. Extensive systems can provide a 35 decibel reduction and intensive roofs can typically reduce noise 65 decibels.
