Green Roof Research

Spurred on by the possibility of specifying a green roof on a domestic extension, I am trying to find out the best system to use in such an application.

From Wikipedia - "A green roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage and irrigation systems."

The benefits are quite beguiling to an eco-freak like me.

1. reduced heating and cooling loads on a building.
2. reduced rainwater run-off
3. can help to filter pollutants from rainwater
4. can help to filter pollutants from air
5. reduced sound transmission through roof
6. visually attractive
7. can reduce the visual impact of a building
   

Given that a lot of information relates to commercial scale roofs, I am going to focus on small scall roofs, and as such found this page on livingroofs.org. which has a very useful PDF which helps to explain the basics of small green roofs.

There are three main types of green or living roof

1. Extensive - a very shallow system suitable for sheds, garages and small extensions
2. Semi-extensive - a medium depth system suitable for domestic flat roofs
3. Intensive - A deep system suitable for commercial applications as it allows for complete gardens to be planted

Of these I will concern myself only with the first two systems, as these are the ones which are applicable in this situation. Essentially we are looking at a structure around 200mm deep that will be low maintenance & will have hardy drought loving plants.

The Green Roof Centre has a number of interesting DIY case studies showcasing a variety of techniques, from the simplest sedum matt upto a deep multiplant roof.

Sedum is the primary plant used in British green roofs. Greenroof.co.uk describes Sedum as follows

They are a versatile and attractive ground cover plant belonging to the Crassulacaea family. Sedums are evergreen, self-generating, drought resistant and capable of withstanding extremes of climate. They flower from early summer through to autumn in shades of pink, purple, yellow and white. Needing very little attention and no mowing or cutting back, they give excellent foliage colour and texture and are attractive to all kinds of insects and birds. Sedums are generally pest and disease free but,like most plants, can suffer from aphids, mealy bugs, thrips or vine weevil which can be controlled by biological means.

Other succulents, grasses, herbaceous perennials and bulbs are also used depending on the project.

Greenroof.co.uk also provides a very interesting product called Nature Mat which is a geotextile base layer preplanted with Sedums etc. which can be rolled onto the substrate of the roof. This can help provide an instant greening effect.

So down to the nitty gritty (there's a pun there somewhere) how are green roofs constructed? again Greenroof.co.uk comes to the rescue with this diagram

As you can see green roofs can be quite complex, although not much more than conventional modern roofs. Especially considering requirements for airtightness and thermal performance which are placed on new domestic roofs of any sort.

Green roofs have been around for years in various forms and one of the most beguiling reasons to have one is that instead of sitting on the landscape, these roofs help your structure become part of the landscape. If that isn't a planners dream... I don't know what is!!
 
If you want more information, then check out this extensive product listing at the green roof directory. If you are considering a green roof for your own project, please email me to arrange a consultation.

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