Green roof systems – why install a grass roof?
Want to install a long-lasting, eco-friendly new roof? Then choosing a green roof system is the answer – find out more about installing a grass roof here.
Covering your roof in grass or plants may seem strange, especially if you live in an urban environment, but green roofs are often more reliable and long-lasting, not to mention eco-friendly, than existing roofingmaterials.
What is a green roof?
A green roof may also be known as a grass, brown or biodiverse roof; but all of these terms essentially refer to a roof covered with vegetation. Green roofs are suitable for almost any type of building be it a house, office, garage or shed. This type of roofing is especially popular in Germany and Scandinavia and is slowly becoming more common in the UK.
“Green roofs would often happen by accident,” says Dusty Gedge, from the Green Roof Consultancy and Livingroofs.org. Speaking at 2011’s Ecobuild show, he explains: “The Germans covered their flammable flat roofs with sand to prevent fire, which then flourished into grass – this is essentially how modern green roofs came about.” There are two types of greenroof:
Intensive green roofs
An intensive green roof is what many people would refer to as a roof garden. According to the Green Roof Centre (GRC), an intensive green roof has a layer of substrate at least 20cm thick which supports a range of trees, flowers, shrubs and vegetation. Depending on what types of plants you choose, an intensive roof will require regular maintenance, as with any garden. It’s important that the building is structurally able to take the additional weight of an intensive green roof.
Extensive green roofs
Extensive green roofs are a more popular option as they are easier to install, maintain and aren’t excessively heavy, so are suitable for more types of roof. The soil layer in an extensive green roof can be only a few centimetres thick and will support tough types of vegetation and shrubs which need little care once planted. To make installation even easier, an extensive roof layer can be rolled out onto the roof in a similar way that turf can be applied to a garden.
Why install a green roof?
Installing a green roof will:
- Cool and insulate a building – “Green roofs are ideal for cooling houses and especially good for cooling in urban environments,” says Dusty. The GFC reports that a green roof can be up to 21 degrees cooler than a conventional roof. In cities, the high concentration of dark spaces absorb heat, releasing it at night-time, which leads to urban areas being up to seven degrees hotter than the countryside. This is known as Heat Island Effect and it can be reduced by installing green roofs.
- Provide sound insulation – a green roof provides a layer of natural insulation which can reduce noise pollution by around eight decibels when compared to a normal roof, reports the CRC.
- Save money on bills – as a green roof naturally cools a property it can reduce any air conditioning costs as well as make your home more comfortable to live in. Dusty points out that a green roof could: “save you 10% on your electricity bills and reduce CO2 emissions by reducing the need for air con.”
- Provide fire resistance – as they hold water, green roofs are naturally fire resistant. Intensive green roofs are particularly resistant as they have a thick substrate layer and contain lots of water.
- Reduce rainwater run-off – architect Jeremy Ashworth explains at Ecobuild: “Our house is called the hairy house because we are growing grasses on it, which reduces rainwater run-off significantly – run-off is the main cause of street flooding.” Flooding is especially bad in cities where there is less ground space to absorb water, so green roofs are particularly good in these areas as they can reduce run-off by as much as 80%, says the GRC.
- Encourage wildlife – green roofs are great for encouraging wildlife and helping to preserve biodiversity which is slowly being eroded as we construct more buildings. Especially in cities, green roofs can provide vital habitats – sometimes particular plants are used with the aim of attracting specific types of wildlife.
- Increase the lifespan of the roof – the GFC claims that a green roof can have double or even triple the lifespan of any other roofing material, partly due to its natural drainage system. Other roofing materials are also eroded by weather and UV rays, whereas green roofs continue to thrive.
- Improve air quality – plants absorb CO2 and help reduce smog which improves air quality in built-up areas.
How much will a green roof cost?
The cost of installing a green roof will vary depending on how big the roof is, whether you choose an intensive or extensive roof system and which plants you wish to use. The GFC says that an extensive green roof can cost between £60 and £100 per square metre and an intensive green roof can cost between £100 and £140 per square metre. Always get at least three quotes for installing a green roof before you hire and check your roofer’s references and insurance credentials thoroughly.