The planting solutions for roofs described as being "steeply sloped" relate to pitches of over 20%. Today, developments in roof greening techniques mean that these sloping roofs can also be planted, even when the pitch is very steep. These highly visible steep green roofs form part of their environment thus allowing building owners to make the most of their building, showing, in practical terms, their sensitivity to plants and the environment. There can be multiple aims: low energy building (LEB), water management, preserving biodiversity or quite simply projecting a "green" image. There is no shortage of original architectural concepts for integrating the building into its landscaped environment. The resulting projects echo our countryside: many different pitches, rounded shapes, variety of colours and volumes.
Using planted systems on steep roofs is different from dealing with flat or gently sloping roofs. Specific problems are involved.
Preventing the risk of vegetation eroding
There is a greater risk of plants eroding in the establishment phase (before the plants start growing and send out roots into the growing medium). Planting techniques involving spreading seeds and planting plugs or pot-grown plants are not recommended for projects where the roofs are steeply sloping. Solutions which are pre-planted in the nursery are the most suitable as the plants start growing more quickly, and have an established root system to protect the soil from erosion.
Protecting the growing medium from eroding
In order to prevent the growing medium from eroding or slipping to the bottom of the pitch (mainly when there is a lot of storm water), barriers to prevent the growing medium from slipping must be installed for roofs whose pitch exceeds 20%.
Compensating for the lack of water
In most cases, the water reserve of the planted system is greatly reduced with the pitch of the roof. This is why automatic watering is highly recommended.
Ensuring regular maintenance
A steeply sloping green roof requires regular maintenance to ensure that the plant cover lasts: weeding, checking the irrigation system, adding fertiliser. Aesthetic results can only be achieved if these tasks are carried out each year.
Performing a technical review of the project
A technical and bio-climatic project review is essential to determine the most suitable system for planting on steep pitches.
| Technical and bio-climatic review -------> | determine the planting system |
| geometry direct environment exposure and aspect excess load roof structure pitch of the roof length of pitch |
plant cover planting system anti-slip device watering system |
