Green Roofs

Sheffield RoofJust back from a very jolly road trip to points north and east – Pickering, Sheffield, Louth, and Malvern. I’ll post a blog on the rest of the trip in a few days. I was at Sheffield University on election day for a BALI workshop on green roofs and living walls, which is an area I’m interested in getting more involved in and promoting actively. With increasing urbanization and improving technology it seems a no brainer. Fascinating stuff it was; we had three expert speakers and a tour of some roofs afterwards. I came away enthused, with a lot of detail and some key impressions…

Green roofs can/will bring fantastic benefits to urban environments. I hadn’t thought much beyond the creation of visually attractive amenity spaces and habitats, but they have other advantages too. They improve thermal and acoustic performance and extend the waterproofing life of a roof, as well as benefitting atmospheric conditions. Interestingly, they also not only reduce the quantity of rainwater run off but also help regulate it, which is apparently becoming an increasingly problemmatic area.

The technology behind living walls is still quite new and on a large scale seems tricky and expensive, but in the long term they could be an integral part of urban architecture in a world suffering from climate change and diminishing natural resources. Right now small units, enabling people can grow their own salad on a balcony, for example, seem a great idea.

Green roofs are more straightforward, but not simple. Although construction methods are tried and tested, a one size fits all approach to design and planting absolutely won’t work and they need to be planned and installed with a great deal of care and attention to detail. There are, however, some really good quality specialists about who can help, and it’s worth spending the money on them to avoid expensive mistakes. I can point you in the right direction if you’re interested.

On the other hand, maintenance of an extensive green roof (as opposed to an “intensive” roof) is surprisingly simple and low key, unless you start with just sedum and want to keep it that way – so have to weed regularly to prevent it being overwhelmed over time by native species.

Extensive green roofs aren’t just about sedum mats (below left), which look good all year round and provide instant effect – but which will be less helpful in terms of biodiversity. You can do much more with the planting to include all sort of species, according to situation and design. The demo section of roof below right started off as a sedum mat with other seeds impregnated in it, and although it wasn’t the best time of year to see it looks a treat, with Sea Thrift, Yarrow, Chives and all sorts. Nice habitat!
Sedum matNatural green roof Around the corner from this area was a raised section with a deeper layer of substrate planted like a traditional herbaceous border for dry conditions – ornamental salvias, Rosemary, that sort of thing…

Formal green roofThe intensive amenity roofs we saw struck me as being rather less exciting and, of course, they require a lot more maintenance. Amazing what can be done though, even 20 floors up, and much better than just looking out at a roof with air conditioning units on!