Flat green roofs can could make a positive impact to your home – aesthetically, ecologically (by replacing vegetation removed at ground level when your house was built) and by providing insulation that keeps you cooler in the summer and warmer in the winter.
There are three basic types of green roofing which you might consider for your home.
Extensive green roofs
Extensive green roofs are fairly shallow, usually with a substrate layer between 50 and 150 mm, and are planted with low-growing and stress-tolerant vegetation, such as hardy grasses, mosses and sedum. They require minimal maintenance and do not put much weight on the building.
Their insulation properties are lower than other green roof types, so conventional roof insulation will also be required.
Intensive green roofing
Intensive green roofs incorporate a thick layer of soil in excess of 200 mm. In this soil you can grow a number of plants from grasses and herbs, to wildflowers and even shrubs. In some cases you are even able to grow small trees.
These types of roof require access for maintenance, so need to be sturdily constructed with ample support, and can often double as recreational spaces. They provide a habitat for wildlife, offer great insulation and water absorption properties, but require a great deal more care and attention -- as much as a comparably sized ground-level garden would in fact.
Semi-extensive systems fall somewhere between the other two types, usually requiring less maintenance than intensive types and constructed using the same techniques as extensive systems. They usually allow for a greater diversity of plant-life than an extensive roof, but have a slightly greater depth of substrate.