Green Roofs: What are the Options?

The benefits of green roofs, and the different kinds available.

green roof

Green roofs have been growing in popularity in recent years, and not without good reason. There are many wonderful advantages to green roofs being used in place of traditional styles, including:

- Reducing heating bills by an average of 4%

- Making planning permission for new builds more likely to be granted

- Retaining an average of 82% of rainfall, as opposed to 27% with a pure gravel rooftop (with figures up to 87% on roofs with a 2% slope)

- Providing a habitat for many species of birds, insects, beetles, spiders, and plants which might otherwise struggle in the area

- Reducing the temperature within the building

- Improving the air quality above the green roof

- Increasing the roof’s lifespan by three times that of an ordinary roof

- Providing sound insulation

- Reducing air conditioning bills

- Improving water quality

The various kinds of Green Roofs

Green roofs are often thought of as just one kind of system for all sorts of uses, but in fact there is a variety of different kinds of green roofs, and some may be better suited to your home or offices than others.

Sedum Green Roofs

Sedum green roofs are most often composed of a range of different species of sedum plants. They are low growing, lightweight, and make one of the most easily maintainable green roofs available. Sedum green roofs are the most popular kind due to their often very beautiful colours and their low-growing nature.

Sedum roofs come in one of three kinds:

Blankets

Sedum blanket green roofs are made of pre-grown sedum turf rolls, usually 1.5m by 1m in size, and each roll can contain several species of sedum plants. Blankets offer an instant green effect as the plants have already been grown by the time the blanket is delivered. Look out for sedum blankets which have been grown on the coast, as the difficult conditions make the plants more robust.

Planted

Sedum planted green roofs are roofs with small sedum plugs planted over the roof. It is recommended that 20-25 sedum plugs are planted per metre square. Plugs should take a few months to develop into a colourful, green roof.

Seeded

Seeded sedum roofs simply have the sedum seeds sown across them. It is recommended that 0.5g of seeds are sown per square metre. The seeds should take just a few months to develop.

Wildflower Green Roofs

Wildflower green roofs are made up of a number of wildflower species. Wildflower roofs work best and look most harmonious in their setting when native species are used. The flowers have several benefits, from reducing the building’s impact on the local environment to creating a semi-natural stepping stone for rare birds, bees, insects, and invertebrates. Wildflower roofs can look vibrant and natural, and if properly planned can flower with different colours throughout the year.

Blankets

Wildflower or wild grass  blanket green roofs are ready-grown for the customer in several strips of up to around 50 species of plant each. They offer an instant green aesthetic as the plants are ready upon arrival.

Planted

Wildflower planted green roofs have wildflower plugs planted across the surface of the roof, usually with around 20-25 species per square metre. These take a few months to develop.

Seeded

Wildflower seeds are sown across these roofs, usually with around 0.5g of seeds per square metre. The seeds should develop within a few months, and a more natural effect can be achieved by using several plant species.

Bio-Diverse or Brown Roofs

Brown roofs are perfect for anyone looking to provide a little extra space for rare invertebrates, birds, bees, and insects. By creating different substrate levels to form undulations, and by incorporating piles of logs to encourage rare beetle activity, a number of different environments can be created to complement a wide range of wildlife varieties.

Intensive Green Roofs

Sometimes, green roofs are not just about aesthetics and lending a helping hand to the local wildlife, but also provide a pleasant and naturally rich environment for the building’s occupants or the general public to retreat to. Intensive green roofs, or roof gardens, are ordinarily situated in easy to access areas in private or public places to create park or garden areas in heavily built up locations.

Sometimes an intensive green roof may not at first glance make itself obvious, as often they can be situated above underground spaces such as car parks, railway systems, or other underground buildings. These types of gardens will usually have much deeper substrate levels (about 20cm in depth) in order to allow for large shrubs and even trees to successfully grow in them. These sorts of green roofs are aesthetically wonderfully pleasing although they do require quite a heavy maintenance regime as well as a complex irrigation system in order to keep them healthy.

Image: Arlington County

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