Green Roofs

Aiming to remain eco-aware in my design work I attended a course on green roofs recently, organised by the Brighton Permaculture Trust and Brighton and Hove Building Green. The tutors were Dusty Gedge and John Little, and we learned about the ethos and theory of living roofs, as well as the practicalities of construction. It was gratifying to meet people from many different countries, and many different disciplines, all of whom were interested in this topic.
Here are some photos of a community building and housing project we visited in Brighton.

What are green roofs?

For anyone who hasn’t heard of green roofs and the benefits they can bring, here’s just a very short introduction. The term refers to a flat or gently-pitched roof (usually less than 30 degrees) with a growing medium laid over a root-resistant waterproofing layer, which supports living plants. Whilst this may seem somewhat unusual to us in the UK, their use is increasing, with cities like Sheffield at the forefront and many others, including London & Brighton, adopting them for many of the situations listed below. They are a centuries-old tradition in Scandinavian countries, and they have been used for a long time in other European countries. Many countries, most notably Germany and many states in the USA, promote their use as part of their town & city planning laws – often requiring a percentage of green roof space as part of the conditions for granting development permission.

Why is this? What are the advantages?

Firstly, and most obviously, is the beneficial effect of adding extra “green space” for aesthetic and ecological purposes – especially in large cities where roof space can be over 75% of the geographical area. However - and here’s why they’re important for planners and commercial interests - they have solid economic benefits. Green roofs can increase the thermal insulation of roofs, resulting in lower energy requirements (and hence lower carbon footprints) for winter heating and summer cooling. The presence of the green roof can help to protect the waterproofing of the roof by removing exposure to UV radiation and reducing the temperature extremes encountered - which prolongs the life of the roof. The evapo-transpiration of the vegetation produces a cooling effect that mitigates the higher temperatures encountered in cities (the “urban heat-island” effect), improving the climate, reducing humidity, and lowering energy demand. The vegetation can also help improve air quality by filtering out contaminants and adding oxygen. Green roofs help to reduce both the volume and rate of rainwater run-off which needs to be managed during storms, giving economic benefits in reduced storm-water engineering requirements and costs.

Don’t they damage buildings and become a maintenance chore?

The answer is most definitely NO! Provided that the green roof is designed to be within the load-bearing capacity of the building and the root-protected waterproofing and drainage is properly addressed, an extensive green roof is very low maintenance.

There are several “flavours” of green roof, mainly associated with the depth and fertility of the soil (more properly, “substrate”) and hence the type of planting which will succeed. These are broadly grouped into:

1) Intensive: these have deep, fertile soil and the planting (perhaps even including trees) is very similar to that in a ground-level garden – in fact, they are more usually described as a roof garden. They require a very high level of maintenance, just as would a ground-level garden, and don’t offer much in the way of additional ecological benefit since the planting & habitat is so similar;

2) Extensive: these have relatively thin substrates – typically from 50mm (2”) to 200mm (8”) thickness and are deliberately of low fertility. In this way they provide very different conditions to ground-level gardens and are colonised by very different plants – mainly low-growing, drought-tolerant, nectar-rich flowering species, often & ideally native, which gives food & habitat to a wide range of insects & invertebrates, and the birds which feed on them. They are very low maintenance, and this form is what is normally meant by “green roof”;

3) Semi-intensive: refers to a compromise between these two extremes, where varying conditions are provided across the extent of a (reasonably large) roof space, such that a mix of habitat and planting can be used – even including food crops.

Where would an extensive green roof be used?

Around the home - on free-standing structures such as sheds, garages, summerhouses, garden offices, fuel tanks & bunkers, etc. or on parts of the main building such as flat-roofed houses or extensions to them;

At schools - they could be used on similar building structures, or for cycle shelters and outdoor shelters or classrooms, perhaps associated with school crop or wildlife gardens;

In Streets - they could be used for street furniture like bus stations and shelters, train platform covers, electricity sub-station roofs and so on;

For commercial properties - they could be used over factory units and warehousing, supermarkets and their trolley parks ... the list is endless!

You can find out more by visiting Livingroofs.org.

Climate Change and Gardens - Blog Action Day

This is Blog Action Day, which this year concentrates on Climate Change. I am pleased to be participating in this important event, which aims to raise awareness of an urgent topic which affects us all - not only from damage to the environment but also with the threats of flooding, famine, increased risk of wars and creation of millions more refugees.

As I’ve touched on before in this blog, the gardener can address in small but important ways the environmental challenges which face the world. Whether by providing better conditions for wildlife (see here and here), growing vegetables in small spaces to save food miles (see here and here), encouraging an interest in the environment in young people, through school gardens, or better handling of rain water through rain gardens, we can all make a contribution. The mass effect of each garden in the world becoming just a little more sustainable would surely make a huge contribution to improving climate change.

Some further things to think about if you’re planning to redesign part of your domestic garden or the outside space of your business:

DO: use reclaimed materials where possible for structures, containers and so on - find a local salvage or reclamation yard and re-use items such as old flagstones, bricks, tiles, chimney pots, scaffold boards, sleepers and other architectural salvage – it will bring character into your garden instead of stark/bland brand-new materials;
DO: use recycled crushed concrete as sub-base material for hard landscaping instead of freshly quarried crushed limestone;
DO: use crushed recycled glass as mulch instead of freshly quarried gravel or stone/slate chips – but only if it’s available locally;
DO: cut down or cut out cement usage in hard landscape elements – cement accounts for more than 5% of the world’s CO2 production – which is more than the oft-criticised aviation industry:
“Concrete is the second most used product on the planet, after water ... No company will make carbon-neutral cement any time soon. The manufacturing process depends on burning vast amounts of cheap coal to heat kilns to more than 1,500C. It also relies on the decomposition of limestone, a chemical change which frees carbon dioxide as a byproduct... Cement plants and factories across the world are projected to churn out almost 5bn tonnes of carbon dioxide annually by 2050 - 20 times as much as the government has pledged the entire UK will produce by that time.”

(http://www.guardian.co.uk/environment/2007/oct/12/climatechange)
DO: use natural stone for garden walls rather than manufactured products if they are available locally; use dry-built stone walls with soil/compost and stone chips to even out the courses rather than cement mortar; planting into the crevices with suitable species (e.g. mat-forming rock garden / alpine plants) as the wall is built will improve the look of the wall and the plant roots will help to bind the walling stone together;
DO: use natural stone paving rather than manufactured concrete slabs if it’s available locally. Wherever possible, for pedestrian purposes, lay it on compacted sand, not cement mortar, and use wider, gravel-filled joints instead of mortar joints – it will look attractive and drain better. Make it even more special by including pockets of planting such as creeping thymes and stonecrop;
DO: ensure your timber, if not reclaimed, is from an FSC source which guarantees that the foresting is sustainable;
DO NOT: use tropical hardwoods without being absolutely sure of their provenance and credentials – the last thing we need is more rainforest cutting down!
DO NOT: use pressure-treated timber if it can be avoided – the chemicals used are mainly petro-chemical derivatives, are harmful to the environment, and the timber cannot be recycled (nor easily used as fuel, due to chemical release) at the end of the product’s life;
DO: consider “composite” decking materials, if you’re planning a deck. This is manufactured from waste hardwood and recycled waste plastic – OK it has a high energy input to manufacture, but it has an extremely long life, and doesn’t need chemical treatment to maintain it during its life;
DO: consider introducing a “green roof” on any flat or shallow-pitched structure, whether a part of your house or an outbuilding. Not only do green roofs look good and add environmental habitat, they slow down and help clean rainwater runoff – especially if used in conjunction with rainwater harvesting or rain gardens. They also add insulation, so reducing energy consumption - which saves you money! The transpiration effect of green roof planting can help to cool city climates in summer, they absorb CO2 and replenish Oxygen in the air as well as helping to filter out gaseous and particulate pollutants. Remember though, to first check the additional weight which will be introduced, and the load-bearing capacity of the existing roof/wall structure!
DO: try to find space for a compost heap/bin to transform your kitchen & garden waste into wonderful soil improver – saves energy of transporting it to the local recycling tip, adds nutrients back into your soil, keeping it “in good heart” - use it as a mulch and let the earthworms do the work for you!

What are your thoughts on how garden design can help fight climate change?
Please add a comment!

Here are 12 suggestions for actions which YOU can take from the Blog Action Day website:

Sign the Tck Tck Tck campaign's "I am ready" pledge supporting an ambitious, fair and binding climate agreement in Copenhagen this fall: tcktcktck.org/people/i-am-ready

Register for the 350.org International Day of Climate Action October 24: http://www.350.org/

Join the UK Government's "Act on Copenhagen" effort to promote a global deal on climate change: www.actoncopenhagen.decc.gov.uk/en

Learn and act with The Nature Conservancy's Planet Change site: change.nature.org

Watch and help promote Current TV's green-themed video journalism at: current.com/green

Support strong climate legislation in the US by making calls to your Senators with 1Sky: tools.advomatic.com/13/calls

Put yourself on the Vote Earth map and upload your photos, pictures and weblinks to show the world future you want to see: www.earthhour.org/home

Put yourself on the Vote Earth map and upload your photos, pictures and weblinks to show the world future you want to see: www.earthhour.org/home

Join the Greenpeace cool IT challenge campaign to turn IT industry leaders into climate advocates and solution providers: www.greenpeace.org/international/campaigns/climate-change/cool-it-challenge

Add your personal story and tell the world what you will miss the most when you lose it to climate change with the United Nations Foundation Climate Board: www.unfoundation.org/global-issues/climate-and-energy/its-getting-personal

Find the latest and most popular climate change actions online at globalwarming.change.org

Join the Causecast community and find new ways to get involved with organizations working to end climate change. Watch videos, read news and support one of the many environmental nonprofits on Causcast. www.causecast.org/environment