Three years ago the London mayor's office and the Green Infrastructure Consultancy studied aerial images of the capital to identify the location and extent of its green roofs. The resulting map charted the location of some 700 projects, covering an area of more than 175,000sq m. Since then, the expanse of green roofs topping the capital's office blocks, shops, schools, apartments and other buildings is estimated to have more than doubled to around 500,000sq m.
That is an indication of how the market for greening buildings has grown in the capital. The UK may not be following the example set by the French government, which last year introduced a law requiring all new commercial buildings to be topped by roofs sporting either greenery or solar panels, but a range of factors are prompting greater uptake of urban greening.
The mayor's London Infrastructure Plan 2050 paved the way for action, notably targeting big business through the capital's business improvement districts (BIDs). This led to such installations as the fruit and vegetable gardens on top of the office blocks of Bloomsbury, Holborn and St Giles.
This could be just a start. Audits of London's BIDs have identified scope to create some 300 rain gardens, 200 green walls and more than 100ha of green roofs, as well as countless small-scale features such as planters and window boxes. A report by Natural England's predecessor, English Nature, published more than a decade ago, found scope to green more than 20,000ha of urban roofscape across the UK as a whole.
Legislation may be lacking but concerns about surface water run-off and health in buildings and cities are keeping urban greening in the political, place-making and public consciousness. Enlightened developers, designers and businesses are also showing an interest in the people-centred approach of biophilic design, which promotes internal and external views onto nature as a guiding principle.
Within the green roofs and walls sector, products, systems and maintenance strategies are all evolving, giving greater confidence to building developers and owners as well as helping to overcome fears of failure. Sarah Cary, head of sustainable places at developer British Land, which routinely tops its developments with green roofs, says: "People are getting much more innovative and creative as the industry has got better at coming up with products and architects have got better at doing it."
Armando Raish, managing director of Treebox, points out that his conversations with architects about living walls have changed, "They're now asking what they can do, rather than basics like what the wall costs," he says. "We're finding a lot more openness to ideas."
That's good news for players at all levels of the industry, whether working with high-profile urban buildings or targeting the growing domestic market, greening house extensions, garages and bin stores.
Extensive, intensive or semi-intensive, sedum, wild flower or brown - green roofs can appear bewildering to the uninitiated. That explains why some industry innovation has been focusing on making things simpler, particularly with the development of ready-planted modules.
ANS Global launched its GrufeKit modular system to meet market demand for simplicity, explains marketing manager Mark Chambers. "We're responding to the fact that roofers don't believe they can install a green roof themselves," he says. "It's a clip-together system so it's simple to install and maintain."
The full kit brings together protection fleece, an optional aluminium guard for the roof edge, Scottish pebbles for footpaths or edging and GrufeTile modules made from recycled HDPE plastic and planted with sedum, wild flower and meadow grass mixes.
Product refinement has been a priority for others in the market, such as Wallbarn, which has made its M-Tray module simpler to install. "We offer it to landscapers, green-roof specialists and even general contractors working for householders," says director Alec Thurbin. Its 500x500x100mm trays are planted with sedum or a sedum and wild flower mix and incorporate Aquaten super-absorbent fibre.
Products such as ZinCo's SolarVert system build up and Bauder's BioSOLAR system can help developers and owners combine green roofs with solar panels without having to penetrate the roof's waterproofing layer. They resolve a dilemma for building owners, says Kieran Townes, senior green roof technician at Bauder.
"It addresses the issue that clients face in having to make a choice between green and solar," he adds. BioSOLAR comprises an integrated mounting solution for the solar panels with a green roof where substrate and vegetation provide the ballasted installation mechanism.
For those developing green roofs, the GRO code of practice is the essential guide. The independent UK body, which represents trade associations, manufacturers and key players in green roofing, addresses such considerations as vegetation species, substrate thickness, potential loading on the building and materials. "We focus on quality as well as priorities like making sure all materials are fit for purpose," says Mike Cottage, deputy chair of GRO and an urban greening consultant and installer.
Green Infrastructure Consultancy director and expert Gary Grant stresses the importance of following the guidance. "If you follow the GRO code, a roof should be fine, but there are a lot of roofs where people don't bother with the correct depth of substrate, which is needed to absorb rainwater".
For designers, however, the planting is also a priority. "Sedum may always be the backbone of the industry, for reasons such as its durability, but there is scope for other solutions," says Joost de Gier, sales manager for Netherlands-based specialist Sempergreen, which recently introduced a bees and butterflies vegetation blanket. The blanket mixes sedum and grasses with some 40 perennial plants and herbs, chosen with the help of the Dutch Bees & Butterfly Conservation Foundation.
Others in the industry are innovating with different planting options. Maggie Fennell, manager of GreenSky at Boningale, says: "Sedums and wild flowers are both quite limited in their range so we're looking to extend that with alpines. They should be good for roofs that are visible and overlooked, as is often the case in London."
The company is no stranger to innovation. It is now three years since Boningale GreenSky launched its Skyplugs, the culmination of a research and development project with the University of Sheffield's Green Roof Centre. The research set out to develop hard-wearing, long-lasting plug plants that would thrive on a harsh rooftop environment. The plugs are nurtured in a mix of peat-free growing medium and substrate to mimic the poor medium in which they are planted out.
The complexity of the supply chain around green roofs for new buildings - involving building designers, main contractors and specialist roofing contractors - can present challenges in bringing innovation to market, says Fennell. "The diverse supply chain means it takes time and effort to get the message across. A green roof crosses over industries and professions."
But there is a clear demand for products promising reliability, she adds: "People seem excited by the idea of getting a range of species that's less likely to fail. Once people have seen roofs that have failed, they really recognise the benefit."
Living walls come in various forms, from trellises to modular soil-based or hydroponic systems and can be used on internal walls as well as external facades. Trellis-style screening, whether wire frame or steel cable, is traditionally a low-cost option and can often be found on functional buildings or around pub gardens or construction sites.
There are many modular soil-based systems on the market, offering permanent and temporary wall solutions. Tendercare's 16-pocket Vertiss modules are popular for temporary uses, such as exhibition displays. Such systems offer a number of benefits, says managing director Andrew Halksworth. "They are easy to put up and take down, and are easy to replant because the cells are just like pots. That allows seasonality to be easily introduced into displays."
Treebox markets its Easiwall range to clients spanning from the homeowner wanting to brighten up a courtyard to developers and owners of major commercial buildings. This year it is launching a vertical rain garden system that combines the Easiwall system with concealed rainwater tanks.
Rain gardens have a potentially valuable part to play in helping urban areas manage rainwater run-off and limit local flooding. Treebox's product has grown out of a vertical rain garden project on Tooley Street in south London (see case study, p35), designed by Green Infrastructure Consultancy and developed through the Drain London sustainable urban drainage action plan.
Like green roofs, living wall systems and their businesses are evolving. "We're becoming more compatible with the construction industry", Biotecture managing director Richard Sabin says of the company's BioWall modular hydroponic system. It relies on Grodan stone wool as its growing medium and has been tested for the kind of attributes usually associated with cladding systems for buildings, such as acoustic performance.
Living walls such as these rely on precision irrigation systems, with remote monitoring. "If you don't monitor then the top is always dry and the bottom is always wet," says Sempergreen's de Gier. ANS Global's remote monitoring capability even tracks the living walls on Crystal Cruises' ships as they travel the world to help maintain the walls in peak condition.
Living walls systems are effective, according to Green Infrastructure Consultancy's Grant, and when things do go wrong "it is not normally a whole wall that fails", he points out. "It is often certain species that suddenly fail and that becomes very evident if they are planted in blocks, which is often how they are designed."
Treebox's Raish explains that one of its walls was installed some five years ago at irrigation and installation specialist Watermatic - one of a number on display on the Hertfordshire company's site - and has thrived since with minimal maintenance. He advises: "The thinner the wall system the more water it will require, as it has less of a buffer. Some people are designing lightweight systems that are design-friendly, but systems have to be plant-friendly first."
The need to tackle rainwater run-off in urban areas is prompting a wealth of innovation, ranging from low-tech vertical rain gardens to systems such as ZinCo's new storm water management green roof system and super-hydrophilic materials capable of holding large quantities of water, such as Aquaten's Aquaten Green. This focus on rainwater attenuation is likely to continue to drive future innovation in the sector.
Another concern in towns and cities is air quality and pollution. Researchers at the University of Birmingham and Staffordshire University have for some time been looking at the potential to capitalise on the natural process of phytoremediation, whereby plants break down pollutants.
US company AgroSci has gone one step further and developed AerogationTM air-purification units (APUs), which push polluted air into plant root zones to intensify the phytoremediation process. A 1x1m APU contains 30 plants including ferns, grasses and small shrubs. Watermatic and Treebox distribute the units in the UK, and Raish reveals that a crowdsourcing campaign is set to be launched this summer with the aim of getting APUs rolled out all across London this year.
Another area of innovation is bioresponsive materials that can emulate specific characteristics of nature. Ecotecture's Sabin is adviser to a research project, being led by London-based Bartlett School of Architecture's BiotA Lab, to develop a biologically receptive concrete wall panel system that is capable of growing micro-organisms directly on its surface, eliminating the need for any mechanical irrigation systems.
There could also be changes in the way the industry operates. Green Infrastructure Consultancy's Grant sees scope for green roofs and walls to join the service economy. Just as music is now a streaming service rather than CDs, green roofs and living walls could be leased for a monthly fee. "In that scenario, monitoring and data become important," says Grant. "There is a driver for innovation, which could possibly lead to more modularity".
Case study: Regent's Place - Diverse microhabitats created on green roofs to boost biodiversity
Regent's Place is a major new development of offices, retail space and apartments created by developer British Land in London's West End. It boasts some 50,000sq ft of green roof space and gardens. The scheme incorporates green roofs on two terraces and a roof, which are either natural or intensively managed.
Consultancy Arup Environmental designed the green roofs for biodiversity by locating diverse microhabitats side-by-side. This was done by topping the waterproof membrane of the roof with a puzzle-like pattern of compartments, made using polyester powder-coated vertical aluminium dividers laid over a reservoir board.
The compartments have been filled with various different growing mediums - to different depths to create different habitats - as well as different seed mixes and plant arrangements. The substrates used include pebbles, crushed brick, limestone chippings, pine bark strippings and pelite, while the planting includes mosses, sedum, wild flowers, grasses, small shrubs and aquatic plants.
As well as having biodiversity value, the roofs are good to look at and provide welcome amenity space. Office occupiers have responded enthusiastically to the green asset, with one, Lend Lease, enhancing it by installing an insect hotel. Another, Aegis Group, has added four beehives.
British Land learned valuable lessons from this and other green roof projects, and now routinely includes them on its buildings. "We now market our green roofs," says Sarah Cary, head of sustainable places. "Occupiers like the visual interest and people like having the space outdoors. They're one of our key selling points."
The puzzle pattern layout of the roofs has been found to be effective in optimising biodiversity and is now being reused by the developer elsewhere.
Biodiverse roof architect: Arup Environmental
Roof contractor Tilbury Contracts, using ZinCo Green Roof and Hydrotech MM6125 from Alumasc
Case study: Tooley Street - Setting a trend for growing development of vertical rain gardens
When a small vertical rain garden was installed on an apartment building in south London's Tooley Street in 2013 it was claimed to be a world first. It was tripled in length two years later and is now being followed by major developments such as Middlesex University's Forum North building in Hendon and the Cambridge Conservation Initiative's David Attenborough building.
The launch this year of Treebox's rain garden system, which has evolved from its involvement in that first 12x2.5m trial wall, looks sure to herald more.
The Tooley Street rain garden arose from the area's green infrastructure audit and was commissioned by Team London Bridge, the local business improvement district. The living wall, now some 30m long, is planted with a mix including grasses, evergreen ferns and some flowers to provide biodiversity and vibrancy in the urban street scene.
Concealed behind the greenery are slimline rainwater-storage tanks, capable of holding enough water to sustain the planting for up to six weeks. The plants absorb water in a controlled way via capillary action, so there is no need for a pressurised irrigation system with power and water supply. The system both stores water for irrigation and attenuates storm water in peak rain periods, limiting localised flooding.
Positive response to the urban greening prompted the wall's extension, but crucially it has also performed well over its three years in place. Treebox managing director Armando Raish says: "If the weather should remain dry for a protracted period, the system is simply watered using a bowser." Green Infrastructure Consultancy director Gary Grant adds: "It has done better than I expected it to. There is potential for low-tech, low-maintenance living walls like this".
||Team London Bridge|
|Design||Green Infrastructure Consultancy|
|Funding support||Drain London action plan (Greater London Authority)|
Suppliers of green roof and living wall products
|Name||Website||Areas of activity|
|Alumasc Roofing Systems||www.alumascroofing.co.uk||Supplier of structural waterproofing and green roofs as well as accessories such as edge protection|
|ANS Global||www.ansgroupglobal.com||Solutions for roof and vertical gardens, interior living walls and logos|
|Aquaten||www.aquaten.co.uk||Supplier of products for water attenuation|
|Bauder||www.bauder.co.uk||Manufacturer of flat-roof waterproofing systems, along with green roof and solar photovoltaic solutions.|
|Biotecture||www.biotecture.uk.com||Designer and supplier of hydroponic modular living wall systems|
|Boningale GreenSky||www.boningale-greensky.co.uk||Plants and substrates for green roofs|
|Sempergreen||www.sempergreen.com||Supplier of vegetation blankets and pre-cultivated hydroponic living wall panels|
|Tendercare||www.tendercare.co.uk||Nursery offering modular living wall design and installation|
|Treebox||www.treebox.co.uk||Supplier and distributor of green walls, living walls, edible walls and green hoardings|
|Wallbarn||www.wallbarn.com||Supplier of Aquaten PlusTM ultra-hydrophilic fabric and green roof systems plus living wall design and installation|
|Watermatic||www.watermaticltd.co.uk||Green roof and living wall design, installation and irrigation|
|ZinCo||www.zinco-greenroof.com||Supplier of green roof build-up systems and accessories|
About this listing
This table comprises companies mentioned in this article, with details based on internet research. Far from comprehensive, it is solely intended to offer readers basic points of contact.