Max Fraser: Living roofs are green houses, important for biodiversity, good for the environment, and facilitating better rain runoff. Old Mayor of London introduced a scheme to promote them, important in cities.
Introducing Joe Swift, presenter of Gardeners’ World, here to talk about living roofs and green walls.
Joe: Ken Livingstone was into living roofs, so interesting to see how this develops with the new Mayor. As our cities become harsher and harsher, green roofs become more and more important. Living roofs and green roofs are basically the same thing, but a roof terrace is different. Intensive roof is one that is viewed as a roof garden, a place to be used, accessed, gardened in, whereas extensive roofs are green coverings, horticultural roofs, whether you can see them or not.
Was on top of Canary Wharf, and a lot of green roofs in that area, planted roofs that can’t be seen by anyone.
Why? What’s the big deal? Why is Germany making it compulsory that 25% of city roofs on new builds be green?
Main reasons:
- look great! don’t want to just see architecture all the time.
- proof that nature has therapeutic effect, lowers stress, blood pressure, increases positive feelings (Ulrich and Simmons 1986).
- good for your soul – when you’re around green, you feel better.
- educational benefits of living alongside nature for inner-city children, who often don’t understand nature at all.
People assume that if you put greenery on your roof you must be damaging it but the opposite is true. Main issue is weight, and need to ensure that your roof is able to cope with it. A lot of green roofs are lightweight, get a bit heaver when it gets wet, but weight is the big issue.
Economic benefits:
- a view onto a green space raises house prices by 8% on average, whether it’s your space or a park or someone else’s roof.
- 60% residents believe value of their home was 15% higher due to green space
- reduces need for summer cooling costs.
Canadians have done a lot of research into this, and show that green roofs help keep buildings cooler, with green roofed buildings generally not getting over 30C in summer.
Misconception – green roofs will insulate your house. They don’t. Pretty minimal effect during winter months, so won’t keep heat in but will keep heat out.
Biodiversity is a big factor – losing biodiversity massively in the city. Gardens are a huge habitat for birds, insects, etc. and when you build on that you loose it forever. So green roofs are very important.
Some green roofs are solely for the birds, which will be attracted by the greenery and the bugs it supports. Study in Switzerland shows that rare and endangered species found on green roofs.
Some people just put in substrate in, the soil and gravel, and let the weeds grow. It’s local plants by self-seeding, you have a natural and local habitat perfect by local birds and insects. Perfect for roofs that won’t be seen – very natural.
Sustainability is the last key issue. We want a sustainable future, and one way that we can make architecture work better is to introduce horticulture alongside it.
Cities get much hotter in the summer than the countryside, is 5 – 6 C hotter, up to 9C hotter in a city in the summer, because the city captures heat. Green roofs can help cool the cities. Can lower temp by 2C.
Storm water retention is much better – water is captured and held by the roof, sparing the drains.
Also potential use for grey water – e.g. a quick shower with low soap levels will be usable for a green roof, although water from a dishwasher or washing machine is too dirty, with too much detergent or particles of food that might attract vermin.
Tomorrow, an area of green roofing 24 times the size of Richmond Park, could be green roofed, they are suitable on many new buildings. We could green up a lot of London tomorrow without doing any structural work.
Green roofs are not new, used to use turf roofs in medieval days, Swedish farm houses had planted roofs. Looks nice, but they used it to protect the roof below, and keep the house cool. Not a new thing at all, even though we think we just invented them.
Case study – Nigel Dunnet on Moorgate Crofts Business Centre, in Rotherham. Covered on Gardeners World. It’s a sedum roof on the top level, then a garden level that’s planted. Put in 6ins of crushed rock and brick as a substrate, with some soil, and planted straight into it. Plants can be very resistant, they will grow very differently, but they don’t all need rich lush soil.
Plant selection is key, but in spring there were primroses, hyacinths and tulips. Later in the spring there were lots more flowers (he names them in Latin, but I have no idea what they were!). Drought tolerant, short-rooted, and not too tall so they don’t grow too tall and get ‘wind rock’.
Late spring the garden is really lush and verdant, lots of variety and not just a static green roof. A real living roof, reflects each season. In early summer, there are red hot pokers, in summer here are purple chives, will grow almost everything, plants that like hot, dry conditions.
Case study – ASLA HQ in Washington DC. used a lot of polystyrene to sculpt the shapes of the land, stacked sheets of it on top of each other to create mounds and interesting shapes. Put compost on, e.g. just a standard compost or special lightweight composts that hold moisture but don’t get heavy. Then a rubber sheet that has holes in it, specially designed for living roots, which just holds the soil in place. Can do same with timber, for example.
Chicago City Hall, has an entire garden on the roof. Greenwich Millennium Village also has a lot of green roofs. People can’t have their own gardens, some have balconies, and often no green space, no private green space at all. Communal gardens, in this case, on top of the car park. Hides the car park, and looks much nicer. In most builds, you just see the car park, but with a bit of forethought, you can put in a garden on top in high-density housing.
Howard Hughes Medical Centre, Research Campus, Virginia, is the largest green roof in north America, with just a 1.5 degree slope so that the water can run off and be captured. When you’re designing, you can do whatever you want. Think about it at an early, conceptual stage, don’t just bung it on after.
Save the Bay, New England, lovely green roof. Toledo Public Library has a park-like green lawn on top.
Those are more commercial properties, but we can all do it on a much smaller scale. Nigel Dunnet has a shed with a green roof. The walls are planted, and the shed is faced with stone. So when you look down the garden from the house, you see the green roof on the shed, instead of a boring old felt roof. Very simple construction – used some posts to hold the weight so that it’s not supported just by the shed, which wouldn’t be strong enough.
You can compartmentalise the roof, just using builders plastic that you’d use for damp proofing, put that on shed, put a couple of sheets of ply, then put soil on it, with some timber compartments to keep the soil on the roof, perhaps use polystyrene planting containers to hold the compost.
You have 6 inches of planting depth, so you need short plants, low spreading plants with shallow roots. Succulents can tolerate very dry conditions, or thyme, sedum which you can buy in pots or as turf.
Can cover anything – garages, sheds, car-ports, any flat roof. Even if it’s just a small area, which you can plant with 2 inches of soil and a roll of sedum turf. If necessary, e.g. if you don’t have any soil, you can just roll out the sedum and it will last five years, at which point you can replace it. Very cheap.
Roof gardens – weight loading is key, if you have a reinforced concrete roof you can put loads of weight up, including trees, soil, furniture. Trees – you have to think about the wind, so olive trees, silver birches, Torbay palms, love the microclimate of London and are wind resistant, so long as you can give them the depth of soil and irrigation. Computerised irrigation needed by some plants, but quite cheap now.
Silver-leafed plants are a clue – they can cope with dry, sunny, windy conditions, e.g. lavenders, grow well in containers.
Green walls. Chelsea Flower Show is soon, and there are going to be lots of green walls there. Children’s centre in Holloway, Paradise Park. Lots of techniques of greening walls, but they all amount to the same thing – all irrigated. At bottom of green wall, is a tank that captures water that trickles down. Get the benefits of biodiversity, get the greening up that’s good for our souls.
Have had to replant a bit, often at the bottom they need shadier plants, at the top they need plants that are happy in the light. Huge range of plants, several have self-seeded like buddleia, the butterfly plant.
Going to see a lot more green walls coming into the architects palette, and hopefully will get garden designers in from the beginning.
Principle is quite simple, get plants anywhere you can. Green walls and roof important especially in the winter when everything’s very dull and grey. In Germany, even the tramlines have turf between them so that it looks like they’re going through a park. Freiburg, collecting the water, installing solar, so they are making 15% more money than they spend on energy.
Why not in this country? House builders have a cartel, they’re not interested in sustainability or design, just interested in their shareholders profits, but until you start bringing in legislation, like they have in Germany, nothing’s going to change. We’ve so many building regs as so far as the interior is concerned, but soon as you’re out the front,door, do what you want.
There is a financial payback. Freiburg cost 10 – 15% more to build, but they are making a profit now.
Where can you find out more? Examples are quite hard to see because they are up on roof. There’s one on top of Kensington Gardens, Derry Street, just off Kensington High Street, which the public can go to. There’s a chap in Tufnell Park with a curved roof that the owner gardens on chained up as there are no balustrades.
Safety issue is important – you have to have balustrades up to 1.2m for a roof terrace. But something like a sedum roof needs no real maintenance. Once it’s on it’s on. No watering – it’s drought resistant. It’s not sustainable if you have to water them all the time.
How much do they cost? E.g., for a standard UK house, a two up two down semi… It’s hard to say how much. Green walls are quite expensive, £200 – £300 per sq m, including irrigation, planting, everything. Green roof, sedum is £10 per sq m, but you can spend up to £200 per sq m on a good quality. Think about the budget realistically, and whether you can afford it.
Retrofitting can be expensive, but plan it from the beginning. An extension is a good opportunity to plan in a roof from the beginning.
Q from floor: Plants for food?
J: Serious green roof campaigners say we should use the roofs for veg, above the pollution zone. All salads you can grow in containers, you can grow potatoes, carrots, etc. and herbs in pots and containers. Tomatoes – all you need is a growbag. A lot of fruit and veg can be grown – anything that’s not too tall. You can get fruit trees in too, but you need to be able to take the weight, and to be careful that the container is well anchored. But small apple, pear, cherry, c an be gown onto dwarf root stock so yes, they can be grown. Nice thought to go and pick, an apple off your tree.
Q from floor: Limited life, the sedum life? Does is have to be replaced?
Yes, sedum tends to die in patches so you can either replant, plug the holes, but if it really starts dying off just chuck it and get some new. It’s a bit like turf, if you’re not going to nurture it a bit it will die, unless you can get up there and feed it. If you can do maintenance on it, you can keep it going, but if you just leave it then it will need redoing after five years.
Q from floor: Thinking of building a house and the planner suggested a sedum roof, but where the house is going to be, there are huge sycamores which self-seed, and I don’t want to have to and weed the roof from the sycamores.
A sedum roof, soil is 50mm, the sycamore is not going to get very big. It will seed, start growing, then will get stunted because there’s no depth of soil. So there will be a bit of competition, and every now and again you may need to tidy up, but they sycamores won’t penetrate the roof, they’ll just be stunted or die off.
Q from floor: Regarding planning, is it an issue? Got a property in Lancashire, and my neighbours wanted some gardens on their roof on a flat roofed sea-front property, and the planners said no.
Need planning consent for a roof garden, but if you just want to plant it up, i.e. not use it as a garden, then they’d have a hard time saying no. With the garden, it’s about safety or overlooking other people’s property. But just greening the roof, it shouldn’t be a problem, but every council and every planner is different.
(Photos to come, hopefully!)
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