What are intensive green roofs?

Intensive green roofs consist of much deeper substrates which give far greater scope to design and grow more complicated and elaborate gardens onto concrete structures. Wallbarn supplies intensive green roof systems with soil substrates over 1 metre deep.

So long as the structure can support the weight, almost unlimited planting and landscaping can be achieved, including large shrubs, grassland, flowerbeds and even trees.

Intensive green roofs tend to be areas where greater access and people traffic is envisaged. A cross section of the system layers is below:

Intensive green roofs offer considerable benefits to the urban landscape far and above anything a light sedum roof can offer. With the increased soil levels and intricate planting, natural gardens and parkland can be recreated on the rooftop level, meaning:

• More diverse vegetation will attract insects in far higher numbers, in turn, increases the level of birdlife in the roof garden.
• Dust and polluting particles will be absorbed – as much as 0.5 kg of particles per m2 at high substrate levels.
• Up to 80% of water can be absorbed by the plants and drainage layers where the substrate is 900mm deep. Intensive green roofs also slow down the run-off during the initial deluge by up to 12 hours
• Insulation properties become much more relevant and economical on intensive roofs. They have been proven to increase the thermal insulation by up to 30% in terms of keeping buildings cool in summer. They have been shown to cool down ambient temperatures by up to 2°C in high-density urban areas. Wet roofs will cool buildings even further.
• Sound insulation can reduce noise by up to 40 decibels in certain applications.
• Lush, luxurious roof gardens have been proven to increase the value and accelerate the take-up of buildings when offered on the market. They pay for themselves medium term.
• The footprint of the building is being optimised. No more wasted space in densely populated areas intensive green roofs are much more expensive to install and will require far more maintenance, leading to higher and long term running costs. It should always be remembered that these are gardens and should be treated as such.

Intensive green roofs are often laid out with considerable hard landscaping areas interfacing with the soft areas. Please see our pages on Universal Support Pads for information on how these systems work together.

The build-up of Wallbarn intensive green roof systems is different from our other green roofs because of the weight and drainage capacity involved. We use a rigid 60mm deep perforated reservoir and drainage membrane to avoid any crushing of the intermediate layers, thus ensuring constant water flow and no blockages.

Intensive green roofs are far more complex than the sedum roofs. Even with lightweight materials being used in the soil substrate, the depth of it means much higher weight loadings on the roof, up to 600kg per m2 in some cases. Therefore different drainage and filtration build-up are required for increased drainage capacity and load-bearing. Structural engineers need to be advised of the stresses involved at the design stage – not at the retro-fit stage.
Designers have to consider the weight of saturated trees, rainwater present in the soil and even snowfall on branches as well as the components as they are installed when calculating the tolerance of the substructure.

As well as the weight of the soil, the higher nutrient level required to sustain vegetation such as trees will need to be effectively filtered before water runoff to prevent “brown water” presenting an unattractive sight in any water recycling systems.

Irrigation is required for intensive green roofs. These types of green roof systems are much more complicated and difficult than sedum roofs. Therefore, they will need far more maintenance and are far more expensive to install and keep in the long-term.