“Garden roofs are promoted heavily in some urban areas for the following reasons:

1. Reduce heat island effect. This is the lingering heat due to black roofs that help hold in heat on warm days. You experience this when you walk through a city on a summer night and feel the heat radiation off of buildings and pavement. (This also occurs with white roofs, but the mechanism is a little different.) Planted roofs do not reflect heat or hold heat.
2. Rainwater runoff: in areas with big rainstorms, the drainage system from the roof to wastewater has to be sized for the worst case. Planting beds help hold water and release it more slowly.
3. Encouragement of birds, butterflies and other wildlife. This is particularly effective in low rise (five stories or less) roofs. Some buildings with restaurant tenants have started growing herbs and keeping bees on the roofs of their buildings.
4. Enjoyment for the building occupants: green roofs have been widely used in health care (hospitals) to make a more pleasant view for the occupants and often a “get away space for the caregivers.
5. Reduction of glare from the roof and the building walls: a planted roof does not reflect glare or heat back into the building.

There are some issues with these from a construction standpoint.

Planted roofs are heavier and the structure has to accommodate that.

Planted roofs either introduce water to the roof or hold it there.

They don't work very well in windy areas. Most planting mediums are less than 6″ thick and they can easily dry out.

Chicago has done very well with green roofs and areas on the east coast have as well. These locations get regular rain all year. Sono più un problema di manutenzione sulla costa occidentale, perché anche Seattle ha tre mesi secchi in estate. La gestione dell'edificio deve essere preparata per la manutenzione continua delle piante e del terreno.

Ci sono diversi sistemi di tetti verdi sul mercato che hanno un buon curriculum negli ultimi 25 o 30 anni. Ho iniziato a fare progetti con tetti verdi circa 20 anni fa e la maggior parte di essi si è comportata molto bene.