Green roof

Why a green roof system?

Following urbanisation and climate change, many studies have already been conducted on the benefits of living roofs and green facades. On the one hand, temperatures are rising; on the other, heavy and unforeseen rainfall is becoming more frequent. This causes flooding and sewer overload in cities. A living roof provides the necessary benefits and can help lower the temperature in urban areas. In addition, sedum roofing contributes to biodiversity and captures some of the rainwater. However, a green roof is more often chosen for its aesthetic green look, rather than for its benefits.

Collection and buffering of water

In his study ‘Technical properties of green roofs and facades‘, conducted during his study at the Faculty of Architecture Mastertrack Building Technology of Eindhoven University of Technology, Nicky Damen (2012) concludes that the retention of water on flat green roofs can reach 75% on average. Thereby, water retention depends on several factors, such as the type of vegetation, thickness and type of substrate. Obviously, water collection and buffering also depend on the current saturation of the substrate. The minimum retention capacity of the MobiRoof ECO system is approximately 20 litres per m². The water buffering capacity can be increased by another 10 litres by adding a buffer layer under the cassette. The water retention does add weight to the roof, but the lightweight cassettes make this buffering of water possible.

The thermal impact of green roofs

Besides collecting and buffering water, a green roof is also an excellent insulation method. A sedum roof provides benefits in terms of a building’s energy requirements. The study by K.K.Y. Liu ‘Engineering performance of rooftop gardens through field evaluation’ (2003) shows that energy requirements can be reduced by 75% for cooling and heating. A green roof has an insulating capacity that can also improve the indoor climate of a building. Indeed, less ambient heat is transmitted from outside to inside, according to the research by Dunnett, N. and Kingsbury, N., Planting green roofs and living walls (2008). On summer days, sedum roofing can block as much as 72% of the sun’s radiation and heat losses to the outside are reduced by about 13% (N. Damen, 2012). However, several studies have shown that the thickness and type of substrate, type of greenery and the degree of insulation determine heat gains and losses.

Sedum roof benefits at a glance

A sedum roof has several advantages.

• Contributes to biodiversity
• Collects and buffers rainwater
• Insulates and dampens sound
• Extends the life span of the roof
• Improves air quality and captures particulates
• Increases the output of solar panels

Green roofing

The MobiRoof ECO roof vegetation system is a ready-to-use system for an extensive green roof. MobiRoof ECO consists of sedum cassettes that can be easily clicked together. The green roof cassettes are filled with several species of sedum. The cassettes also feature a substrate that provides drainage and water storage. MobiRoof’s sedum roof trays can be applied directly to the roof covering. However, if no root-resistant roof covering has been applied to the roof, it is recommended to apply a root-resistant vapour-permeable membrane first.

Roof cover plants

The sedum roofing plants consist of 6-8 different plants per cassette. The sedum consists of several species including Album, Spurium and Reflexum. There are 4 cassettes going into one m², creating a nice mix of sedum plants on the roof. The succulent requires little maintenance and can withstand drought well. This makes the plant excellent for roofing. The roofing plants used in the cassettes in the MobiRoof ECO system are grown at Mobilane’s production site under “On the way to PlanetProof” certification. This independent seal of approval proves that the sedum plants for the MobiRoof ECO are sustainably produced and are therefore a better choice for nature, climate and animals.

Maintenance of sedum roofs

A green roof does not require much maintenance, and because sedum is hardy, it stays green all year round. Thanks to the water buffering capacity of the sedum roof trays, irrigation is virtually unnecessary, but a sedum roof does need maintenance once or twice a year. The sedum roofing should be fertilised with sedum fertiliser in spring. And in September, the spent plants should be pruned and unwanted weeds removed. Moreover, it is important to keep the rainwater drains clean.

Different applications of living roofs

A green roof is not only suitable for flat roofs, but can also be installed on roofs with a slight pitch (up to about 20% or 10 degrees). To use MobiRoof ECO on roofs with a higher pitch, an additional fuse, such as an L-profile, must be fitted. This makes a green roof possible not only on a shed, canopy, or garden house, but also on houses and utility buildings. Green roofs can also be found on bus shelters, covered cycle shelters and car parks. The applications of green roof cassettes are very diverse.

Circular green roof system

Sustainability can be divided into ‘durability’ and ‘sustainability’. Durability refers to the life span of a material or product. Sustainability looks at how environmentally friendly the material or product was created. But also, whether the material is recyclable. A Mobilane green roof system meets both these sustainability requirements.

Sustainable

MobiRoof ECO is a circular green roof system where the sedum cassettes are made of recycled plastic and produced in the Netherlands. Not only that, but the cassette is also fully recyclable. This reduces pressure on the environment and limits waste streams.

Durable

Green roofing contributes to the lifespan of roofs. Several studies have examined and concluded this. The green roofing reduces the temperature on the roof covering (membrane) which increases its lifespan. Also, UV radiation does not reach the roofing directly and because it is covered with plants, the roof will suffer less physical damage.

Lightweight sedum roof

The green roof cassettes are also lightweight, allowing the MobiRoof system to be easily and quickly applied to all kinds of buildings without the need to modify the supporting structure. A filled cassette with sedum plants weighs about 38 kg per m² and about 58 kg per m² when fully saturated with water. An additional advantage is that the green roof cassettes can be repositioned and sawed through, so that the roof can be arranged completely as desired and customised. The light weight and compact size make it possible to install the sedum roof covering yourself. However, gravel should be applied to the outer edges of the roof and around e.g. skylights and near drainpipes to promote the microclimate and prevent wind influence under the cassettes.

Green roof with solar panels

Solar panels convert solar energy into electricity, but unlike their name suggests, solar panels do not work as well as they get hotter. A green roof helps the equipment stay cooler so you get more efficiency from your solar energy. On a black flat roof, temperatures can reach as high as 85°C in summer, on a sedum roof the maximum temperature is around 35°C. Solar panels have the best efficiency at an ambient temperature below 25°C. A green roof therefore allows the solar panels to operate longer at their maximum capacity because the roof heats up less quickly.

A green roof with solar panels has other advantages. For instance, the solar panels create shady patches that allow butterflies and insects to ‘hide’ there during the hottest part of the day. In addition, sedum plants are succulents that store moisture in their leaves so they burn very badly. So, should a fire occur due to the solar panels, the green roof acts as a fire retardant. Have solar panels already been installed? Even then a green roof can simply be laid under and around the solar panels. It is therefore not necessary to temporarily remove the panels.

Green roof subsidy

A green roof contributes to making the environment more sustainable. Therefore, its construction is encouraged by making subsidies available. This can be as much as €40 per square metre. This makes the purchase and construction of green roofs a lot cheaper. How much the subsidy is for a green roof and also which conditions have to be met differ per country. In addition, there is a subsidy ceiling. Each government agency has a certain budget for green subsidies, which is the amount available during a period of time. Therefore, find out in advance whether the ceiling has already been reached. Often, the rule is: first come, first served.