Not just for tellytubbies, green roofs look good, they’re eco-friendly, they save you money, and no, they don’t need mowing…
Berkeley Court, NW1
It has been said that if you added together all the flat roofs in London you would have an area 24 times the size of Richmond Park. But maybe their barren asphalt days are numbered.Green roofs (AKA living roofs or brown roofs) were popular in the 1930s – one of the largest in London is the crowning glory of Berkeley Court, a monumental mansion block in Marylebone.
Now, thanks to growing eco-awareness, they’re enjoying a renaissance that finds them topping buildings from the tallest of towers to the smallest of garden sheds.
But what is a green roof, why would you want one, and how much will it cost? Below is a quick eight-point guide to making your roof as lush and interesting as your garden.
It’s basically a roof with plants growing on its surface. This can range from moss and grasses that have grown spontaneously, to an elaborate roof garden complete with shrubs, trees and hard features.But the sort of green roof that is gaining popularity fast is not usually a recreational space. It is made up of a low covering of plants that thrive on neglect in the normal, harsh conditions of the roof.
First of all, they can look great, and anything that turns an ugly asphalt roof into a flowering mid-air meadow can’t be a bad thing.But, more importantly, a living roof reduces the environmental impact of the building it tops, retracing in green the footprint of your home and providing valuable space for flora and fauna in a residential area.
They’re good for householders, as they can extend the life of your flat roof and save fuel by reducing heat loss in the winter, and preventing heat gain in the summer.
And they’re good for your neighbours too. A porous roof reduces the volume and rate of rainwater that normally pours off a hard surfaced roof, lessening the risk of flash flooding.
Herein lies the problem. Green roofs are ideal on flat-roofed structures, or inclines of up to nine degrees, but most of us live in houses with pitched roofs.A slope of up to 35 degrees is possible, with retention measures in place, but much more than that and they can become unviable.
However, smaller level spaces, such as flat-roofed extensions, garages, and even garden sheds or porches can host a living roof and its accompanying flora and fauna quite happily.
Of course, wherever you decide to put your living roof needs to be strong enough to support the plants and substrate when soaked. It is likely to weigh around a third more than ordinary tiles, so seek professional advice if in any doubt.
Firstly waterproofing and insulation is laid, followed by a drainage layer. Then comes the substrate, made mainly of crushed bricks, and finally the plants.Cuttings and seeds can either be spread on the prepared substrate and overmulched, or rooted young plants can be used to establish the plant cover.
If you’re in a hurry a few companies also provide a ready-made mat which is grown to maturity elsewhere and can be rolled out on the substrate to provide an instant green roof.
Because of the difficulties of regular maintenance, the look most people aim for is more low-lying wild garden than croquet lawn.A fairly wide range of flowers and foliage can be planted, as long as the plants you choose do not require too much depth and can withstand the harsh roof environment.
Types of sedum, an evergreen succulent, which flowers in shades of pink, purple, yellow and white, are commonly used as they are self-generating, drought resistant, and need no mowing or cutting back.
But for the more adventurous, other succulents, grasses, herbaceous perennials and bulbs can be used.
But whatever you plant will soon be joined by native plants, insects and birds.As Dusty Gedge, co-founder of livingroofs.org, an independent green roof organisation, points out, nature doesn’t just live in the countryside.
“Living roofs are very good for many species of insect that are becoming rare in the wider countryside, such as rare bees, spiders, beetles, and ants, and they don’t impact on the roof.
And then there are the birds that will feast on the high-rise insects. In particular the black redstart, the bird that has been promoted as a cultural icon for London.
It is one of our most endangered birds, and it prefers to hunt for spiders and insects in the rubble of urban power stations, industrial units and dilapidated wharves.
But with its brownfield haunts being lost to new developments, several local councils have insisted on green roofs being built to create a network of foraging areas in the rooftops of the city centres.
According to Dusty Gedge it is perfectly feasible for an experienced DIYer to create a roof garden on their garage or shed. (For instructions see the Living Roofs website).But, for a bigger job always go to the professionals, preferably someone
who works within the German FLL Guidelines.
According to John Williams at Blackdown Horticultural Consultants, who takes on residential as well as larger green roofing projects, a professional job could cost you from around £55 to £120 per square metre on top of what you might pay for an asphalt roof.
Not to install one on an existing roof. And if you are planning a new build it’s rumoured that the inclusion of a green roof may encourage planning departments to look more kindly on your application.At a governmental level, although green roofs received an official thumbs up from housing minister Yvette Cooper recently, we are still a long way from seeing the compulsions or financial incentives offered in other European capitals.
But, even without government incentives, Dusty Gedge says a green roof can save you cash. “If you move into a property with a good green roof you will save money on cooling your property in the summer time.
“You will see some savings in the winter, but the real financial gain is in the summer. In the future cooling is going to become very very important. The green roof on Canary Wharf saves 20 per cent in the summer, that’s £5,000 a year.”
And with global warming looming, the green roof brigade may have struck on something we can all do to help. 20 to 30 years ago people laughed at people like me who were worried about green issues,” says Blackdown’s John Williams.
“I think in 100 years time ten per cent of this country will have green roofs. It’s just common sense.”