Here is an interesting PDF giving key facts about green roofs. The most interesting thing is a study they did comparing an R18 insulated roof with a non-insulated green roof. The green roof was a lot cooler in the summer. They also give costs and life assessment numbers. Very interesting.
One of the things Brooklyn brownstone owners ask us is the effect of a green roof on their heating and cooling. We suggest installing a green roof with insulation under it. This way the insulation adds to the heating benefits in the winter and the green roof adds to the cooling benefits in the summer. You get the best of both.
A green roof doesn’t do much in the winter to help a brownstone keep warmer. It does help break the wind and during windy times the heating benefits of a green roof do exist. But overall a green roof in the winter is closer to a block of ice than insulation – think wet earth.
But in the summer a green roof is very helpful. When you wet your skin with water the wet area feels cooler. That is because the water is evaporating and taking your body heat with it. Plants give off water from their pores in the exact same way. This keeps them cool and in turn keeps your roof cool.
As Brooklyn green roof specialists we try to combine the green roof installation with an integrated approach. So we look at more than the plants on the roof. We like to incorporate a gray water system for example. So when people shower and use the sink the water is passed to the roof. This eliminates watering and allows you to have a more exotic green roof. We also find that bees are a nice addition to a green roof. The plants and bees have a beneficial relationship.