Green roofs are becoming increasingly popular for their positive environmental, social and economic impact.
It has many advantages. Among them:
- Environmental: more biodiversity, water management, reducing urban heat islands
- Economical: longer life for the waterproofing layer, energy conservation in the building thanks to improved thermal insulation
- Social/public health: aesthetic pleasure, sound insulation, better air quality
Depending on the desired visual effect and the weight your building structure can support, there are three types of green roof: extensive, semi-intensive and intensive.
The plant component has the greatest impact on the services provided by the green roof: aesthetics, biodiversity, cooling, etc. This plant layer must be chosen according to local climatic conditions, maintenance and watering capacity, as well as the exposure and slope of the roof.
Depending on the choice of vegetation and the weight the structure can bear, the choice of substrate and its thickness is crucial.
The substrate allows vegetation to develop, providing anchorage for roots, water and the nutrients needed for growth. Fertilization needs to be adjusted over the years to maintain attractive vegetation.
Water-saving irrigation will ensure the survival of plants and a positive visual impact over the long term. Thanks to irrigation, vegetation can cool the ambient air through evapotranspiration.
The ODISI solution enables both drainage and irrigation of plants: it secures the establishment of vegetation while saving water.
What factors need to be taken into account when choosing a green roof?
- Budget
- Slope of the roof
- Roof loading capacity
- Desired function (biodiversity, water retention)
- Aesthetics
Everything you need to know about extensive green roofs:
What are the advantages of extensive green roofs?
- Lightweight (80 to 180 kg/m²): easier to install, even in renovation projects
- Light substrate (approx. 10 cm)
- Low-growing vegetation (moss, sedum, etc.)
- Low maintenance and low cost
- Suitable for low-slope roofs from 1% to 20%.
- Suitable for greening large roof surfaces
The disadvantages of extensive roofing:
- Less ecological interest: limited variety of plants
- Limited aesthetic appeal
- Low rainwater retention
In extensive vegetation systems, the ground cover is as self-sufficient as possible. It has a strong capacity to cover the soil (colonization, self-regeneration) while being resistant to climatic hazards (frost, drought). Perennial plants such as sedum are the most common. Bulbous and rhizomatous plants, annuals, biennials, mosses and small woody plants can also be used.
Care must be taken to select the right type and thickness of substrate, as well as the maintenance required. The weight of the plants at Maximum Water Load must also be taken into account when calculating the loads borne by the building structure. For extensive planting, the average weight is 10 daN/m².
Although this type of vegetation is more resistant to drought, a drip irrigation system such as the ODISI sprinkler system will ensure that the plants grow well and survive for many years to come.
The recommended minimum frequency of maintenance is 2 times a year, to remove any garbage, clean rainwater drainage systems, check vegetation growth and weed control, mow or cut back any grass, fertilize, etc.
Everything you need to know about semi-intensive roofing :
What are the advantages of semi-intensive green roofs?
- Intermediate type (150 - 350kg/m² load)
- Medium thickness substrate: 15-30cm for better water retention
- More varied vegetation: shrubs in addition to moss and herbaceous strata
The disadvantages of semi-intensive roofing:
- Pente de toiture plus faible < 5%
- Moderate maintenance: about 5 passages/year
- Watering essential
- Higher costs
In semi-intensive green roofing systems, the plants are more diversified, with a greater substrate thickness. Biodiversity is higher, thanks to vegetation that can include larger woody plants in addition to the vegetation possible with extensive roofing. Grasses are also often used for their visual appeal and hardiness. Appendix D of the RP TTV provides details of the plants commonly used for extensive and semi-intensive roof greening.
Maintenance is longer and more regular (at least 4 a year) to maintain the balance between the different plant species, for mowing, pruning...
Note that the slope of the roof must be less than 5% to support this taller vegetation. Likewise, the structure must withstand a higher weight: low-growing shrubs have an average weight of 20 daN/M².
Watering is essential to ensure the survival of this vegetation. We recommend ODISI for drainage and irrigation of plants.
Everything you need to know about intensive green roofs :
What are the advantages of intensive green roofs?
- Thicker substrate (approx. 30 cm or more)
- Deeper-rooted vegetation: trees, shrubs...
- Creation of an ecosystem in an urban environment, with a wide variety of species.
- Greater water retention capacity
- Visual aspect and access to nature
The disadvantages of intensive roofing:
- Heavier (over 400 kg/m²): load can be a constraint to installation
- Higher maintenance and more expensive
- Regular watering, tree and shrub pruning....
- Greater need for expertise
- Higher cost
Intensive green roofs are more complex and enable the creation of real landscaped areas on the roof: vegetable gardens, rest areas, leisure zones... Their great diversity enables carbon storage and greater biodiversity, as well as increased cooling.
The maintenance requirements of such a roof, and the cost of installation, are greater. Careful attention must be paid to irrigation and frequent maintenance, including fertilization and pruning.
