Intensive Green Roof Thickness

Intensive green roofs offer a great potential for design and biodiversity.

Intensive green roof thickness.

Intensive systems allow the designer to create a park like setting so they are the best option for roof gardens that will be occupied. Plant selection and design greatly affects the maintenance required for the upkeep of these roofs. Extensive roofs are thin lightweight roof systems that typically have a planting media measuring 6 to 20 cm deep while heavier thicker green roofs are known as intensive roofs and their growing media ranges in thickness from 20 cm to 100 cm. An intensive green roof is a deeper typically greater than six inches heavier system designed to sustain complex landscapes.

A typical growing medium depth of an intensive green roof is 6 inches or more. This system supports everything from small personal home gardens to full scale public parks. They fall into three main categories extensive intensive and semi intensive. Once the plants are installed and the soil is moist these rooftop green spaces can weigh as much as 150 pounds per square foot.

Intensive green roofs weigh from 35 pounds to beyond 100 pounds per square foot when dry it is all a matter of the soil depth which is affected by the amount of mounding that is used. The nominal thickness of a green roof is the approximate total height of the soil and drainage components that constitute the green roof system excluding the roof structure insulation waterproofing and plants. A green roof with a lightweight solution of 30 kg m2 is only possible with sedum vegetation and a green roof with a weight of 220 kg m2 is composed of a combination of sedum grasses herbs or host plants. For intensive green roof profiles a drain restrictor may be used to retain water in the base of the profile for subsequent plant transpiration.

Semi intensive green roofs as their name states are a combination of the aforementioned two types. Intensive to describe green roofs that are thick enough. Although there are no precise definitions of them an extensive green roof has a shallow growing medium usually less than six inches with a modest roof load limited plant diversity minimal watering requirements and is often not accessible. The planting medium in intensive green roofs starts at 6 inches although you will see some wiggle room in various definitions and really elaborate designs may exceed a couple feed.

Sloped roofs retain less water in general and the moisture content varies from the ridge to the eave lowest edge of the roof. It is common practice to use the term extensive to describe green roofs that are very thin and will only support hardy drought resistant vegetation such as sedums herbs and perennials. The weight of an intensive green roof system is critical for a particular type of plant and the minimum intensive green roof thickness should ranges from 150mm for a wild grassland 300mm for bushes and 3 meters in height and at least 400mm upper substrate and 250 mm lower substrate for small trees of approximately 10 meters.