ALIVEAND WELLBRINGING NATURE BACK INTO BUILDING DESIGNDesigning sustainable buildings doesn’t always mean hi-tech solutions. From green roofs toliving walls to constructed wetlands, sometimes it’s just a matter of embracing natural so-lutions. Lenny Antonelli investigates the emerging technologies and designs that use natureto improve the performance of buildings.

CI 39

When Erik van Lennepsays he wantsbuildings to begreener, he meansit literally. “Ourgoal is to maximisegreen roof cover-age in Dublin,” hesays. That goal couldsoon be within sight,

as Dublin City Council takes the first stepstowards embracing green roofs.

Van Lennep, the founder of sustainabil-ity consultancy Tepui, has preparedguidelines on the types, functions andadvantages of green roofs for DublinCity Council’s planners. His guidelinesalso recommend the introduction of agreen roofs policy for the city, and theinstallation of green roofs on existingcouncil buildings. “At the moment we’rejust giving advice to our planning de-partment. It’s up to them to requestgreen roofs,” says Mairead Stack, DublinCity Council’s biodiversity officer, whoalong with van Lennep has been at theforefront of pushing green roofs in thecity. “We’ll be strongly trying to incorpo-rate a green roofs policy into the coun-cil’s next development plan,” she says.

Such a policy could request developersto include green roofs in certain cases.The Greater London Authority’s latestdevelopment plan demands major devel-opments to “incorporate living roofs andwalls where feasible.” In Basel, Switzer-land, all new and renovated flat-roofedbuildings must be greened to a depth ofat least 10cm, while in the Austrian cityof Linz all new flat-roofed buildings over100m2 must include green roofs.

Green roofs aren’t a new technology.Newgrange is the earliest surviving Irishexample, while in northern Scandinaviasod roofs and walls, some still surviving,have been around for centuries. The de-velopment of modern green roofs beganin 1960s Germany, and it is estimated thatten per cent of the country’s flat roofs havesince been greened.

There are three basic types of green roof.The extensive variety reaches a depth of200mm, is light and easy to maintain, andfeatures moss, sedum and grass species.Intensive green roofs can be up to 500mmdeep, and the roof must often be designedspecifically to support this heavier load.Regular maintenance is needed, but theycan support all types of trees and shrubs,and act as true rooftop gardens. Semi-in-tensive green roofs sit in between; theyrequire moderate structural support, andare limited to shrubs, perennials and grasses.German company Bauder has been sup-plying both extensive and intensive greenroof systems to the Irish market for manyyears, including landmark eco buildingsfeatured in previous editions of ConstructIreland such as Navan Credit Union, Dain-tree, and Mater Orchard, to name but a few.

The basic components of most green roofsare the same: a frame to hold the soil inplace (often made of timber), a waterproofmembrane, root barrier layer, drainagezone, growing substrate, and vegetation.

Some modern examples of green roofsare striking. The Acros building in Japan’sFukuoka city features a series of terracedgreen roofs that reach 60 metres in

height, merging seamlessly with an adjacentpark at ground level, while Ford’s RiverRouge factory complex in Michigan boaststen acres of ‘living’ roof - the world’slargest - designed by noted green architectWilliam McDonough.

But green roofs are more than an archi-tectural statement designed to green thegrey urban environment. They offer im-pressive practical benefits too, such asdrastically reduced rainwater runoff, in-creased urban biodiversity and impres-sive insulation performance. They alsoprovide green space in dense urban areas,and help to cool local temperatures. “Theytick all the boxes,” Mairead Stack says.

As global temperatures rise, green roofscan play a key role in mitigating the ef-fects of climate change in urban areas,where artificial surfaces absorb heat andbuildings dominate the skyline, raisinglocal temperatures above those in thesurrounding countryside (the urban heatisland effect). By evaporating water and

absorbing less heat, green roofs reducelocal temperatures. The surface tempera-ture of Chicago city hall’s green roof canbe as much as 44oc cooler than conven-tional roofs nearby, while in Toronto re-searchers concluded that if all possibleroof space in the city were greened, itwould lead to a 0.5 – 2.0oc reduction incity temperatures.

Greening a roof can affect temperatureswithin buildings too: a green roof can re-duce summer temperatures underneath theroof membrane by 15oc and raise wintertemperatures by 2.5oc, according to a studyconducted at the University of Nottingham.

From an engineer’s perspective, the abilityof green roofs to reduce rainwater runoffis impressive: research carried out in thetemperate Pennsylvania climate concludedthat an extensive green roof can reducerunoff by up to 100 per cent in summerand 30 per cent in winter.

Green roofs can also neutralise acid rain

(above) The sand roof of the Okowerk Environmental Centre in Berlin was built in the1890s, and is now colonised by mosses and lichens; (below) the moos filtration plantnear Zurich in Switzerland features nine acres of extensive roof meadow that supports175 different plant species, including rare green-winged orchids; (opposite) the ACROSFukuoka building in Japan's Fukuoka city features a series of terraced green roofs reach-ing 60m in height

Photo

s on t

his

pag

e co

urt

esy

of

livin

gro

ofs

.org

/

(P38)

Photo

: Tan

aka

Juuyo

h

(above) An extensive green roof in Freiburg, Germany features an array of Solar PV cells. Green roofs assist solar PV technology by cool-ing rooftop temperatures. Overheating is a key reason for inefficiencies in PV technology; (below left) the green roof on law firm Allen& Overy's London headquarters; (below right) a stand-alone living wall in the Millennium Park, London

CI 41

and sequester carbon. “We’ve tested a typicalsedum roof, and the amount of carbonsequestered is small,” Brad Rowe, associ-ate professor of horticulture at MichiganState University told Construct Ireland.“It’s comparable to desert scrub. But ifyou have something deeper it’ll have morebiomass, and it’ll sequester much more.Even with a sedum mat though, it’s morethan is sequestered on a typical roof.”

With the principles of sustainable drainagesystems (SuDS) - including the demandthat runoff in new developments should

not exceed that of a typical greenfield site- enshrined in the development plans ofevery local authority in the greater Dublinarea, green roofs could soon become acommon facet of new developments inthe city. “The most practical way of meetingthe requirements of SuDS in a high den-sity area is to use a green roof,” says DonMcEntee, senior engineer with DublinCity Council, though he says that perme-able paving is another viable option.

McEntee says that green roofs can have apositive effect on local water quality too.

In Dublin, roof drainage systems carrywater directly into the sewage network.When the sewers fill during heavy rain-fall, diluted raw sewage flows into theLiffey. Because green roofs absorb somuch rainfall, they ease pressure on sewagesystems and reduce overflow into localrivers.

Intuitively, green roofs can boost biodi-versity in urban areas. Environmentalconsultant Dusty Gedge says that his in-terest in green roofs developed from hiswork on bird conservation in London. “I

(top)

Photo

: liv

ingro

ofs

.org

/ (

bott

om

lef

t) P

hoto

: liv

ingro

ofs

.org

CI 43

was working on the conservation of theblack redstart, and I thought, why don’tthey just put the habitat on the roof?”says Gedge, who estimates that betweenexisting green roofs and planned futureones, there will soon be 700,000 squaremetres of green roof in London.

With a background in biodiversity, Gedgeisn’t a fan of homogenous sedum mats.“The construction industry is very mech-anistic. It likes everything to be the same,whether it’s paving or bricks…a greenroof is essentially a landscape. If you’rebuilding a green roof near the Burren, theBurren should essentially be the green roofat land level.”

Mairead Stack says that Dublin City Councilis also examining the concept of biodi-verse roofs, on which a material such asgravel or concrete is laid at varying heightsto create a diverse topography that repli-cates brownfield sites. “Brownfield siteshave one of the highest biodiversities. Youget a whole lot of very rare plant and in-sect species,” she says.

Green roofs are compatible with othersustainable rooftop technologies, suchas solar thermal arrays and rainwaterharvesting systems, and green roofs caneven improve the performance of solarphotovoltaic (PV) systems: by reducinglocalised temperatures they prevent PVpanels from overheating, an often-citedreason for inefficiencies in PV technology.

Clearly green roofs boast an impressivelist of benefits, but are they cost-effective?While additional materials and labourcan add up to 30 per cent to the costcompared to a conventional roof, thiscan be offset by savings from reducedenergy consumption and roof mainte-nance. By sheltering roof materials fromthe weather, green roofs can double oreven treble their lifespan, according toresearch from Penn State University.

Dusty Gedge believes that attitudes towardsgreen roofs are changing: “Six years agonobody talked about climate change, andnow people are interested in the urbanheat island effect, energy performance,storm water attenuation and growing foodon green roofs,” he says.

While green roofs are growing in popu-larity, their vertical equivalent has somecatching up to do. Perhaps the most fa-mous green walls are those gracing Parisianstreetscapes, designed by French botanistPatrick Blanc. In Paris, subsidies are availablefor residents to install green walls onbuilding facades. The city authoritieseven look after maintenance. “They don’thave any more places to green on theground, so they’re going up the walls,”van Lennep says.

Outdoors, there are two types of green wall.Common green facades are facilitated withsimple trellising. In other cases, vegetationis rooted in soil or an inorganic growingmedium, often in pre-vegetated panelsthat are installed over the building structure.“These are highly engineered systems,”van Lennep says.

Like green roofs, green walls offer practi-cal benefits: they create a dead air spacethat provides thermal insulation, cut downdaily temperature fluctuations at the wallsurface by up to 30oc, and reduce wind

chill by up to 75 per cent (with a knock-on reduction in heating demand of up to25 per cent). They also remove pollutantsfrom the air, help to counter the urbanheat island effect and sequester carbon.

It’s not just outdoors that you find greenwalls though. Van Lennep says that ‘active’green walls can help to improve indoorair quality by removing pollutants. “They’rehooked up to an air handling system. Fanscirculate air around the building and pushit through the padded roots, and that scrubsthe air,” he says.

Green roofs and walls are just one way inwhich biology and engineering combineto make buildings more sustainable.Constructed wetlands are another. Essen-tially artificial marshes, constructed wet-lands are a low-energy method of treatingwastewater, sewage, or effluent from in-dustry or agriculture.

Vegetation in the wetland acts as a sub-strate on which micro-organisms grow,breaking down organic matter. Com-bined with natural chemical processes,this removes 90 per cent of pollutantsfrom the water. The plants themselvesremove seven to ten per cent of pollu-tants, and absorb nutrients such as ni-trogen and phosphorus. As differentaquatic plants take up nutrients andheavy metals at different rates, a con-structed wetland is designed speciallyfor the type of wastewaster it’s treating.

There are two basic types: subsurface flowwetlands, where effluent flows through agravel or sand medium in which wetlandplants are rooted, and surface flow wet-lands, in which effluent moves above thesoil in a planted marsh or swamp. Livingmachines, a variation of constructed wet-lands, are highly engineered systems inwhich wastewater is remediated as it ispumped through a series of tanks, each aunique microhabitat designed to treatspecific elements of the wastewater stream.In temperate climates, living machinesare often kept in greenhouses to main-tain the temperatures needed to stimu-late biological activity.

Dublin’s only constructed wetland, in theTolka Valley Park, treats water from theheavily polluted Finglaswood stream be-fore it enters the Tolka river. To ensurethe system is effective throughout theyear, the wetland is planted with a selec-tion of species that exhibit a varietygrowing seasons. “We’re trying to getthree more (constructed wetlands) upand running in Dublin,” McEntee says.

Dublin City Council is looking at innova-tive wetland projects pioneered by otherlocal authorities. Thirteen farms aroundthe village of Dunhill in County Water-ford have developed wetlands, and waterquality in a local river has dramaticallyimproved. “Ten years ago the Anne riverwas totally polluted. Now sea trout areswimming back up,” McEntee says.

The village of Glaslough in Monaghan hastaken things further, treating its sewageeffluent with a wetland system. Wastewaterflows through four ponds sequentiallybefore being monitored in a fifth pond.“It does a better job than a conventionalwastewater treatment because it will removethings like hormones that conventionaltreatment can’t. You get a cleaner efflu-ent from a wetland than from wastewatertreatment,” McEntee says.

With leaking septic tanks being partly re-sponsible for widespread pollution in Irishwaterways, the potential for constructedwetlands is obvious, particularly in ruralareas where the cost of bringing conven-tional sewage treatment is often prohibi-tive. So why are there so few?

“There’s total scepticism around it,” McEnteesays. “The only way to get over that is tochampion a project and prove that it doeswork. Take Glaslough for example, it had

Some examples of renowned Frenchbotanist Patrick Blanc’s living walls abroadinclude (top) the Musée du quai Branly inParis; (above) le Mur Vegetal at MelbourneCentral, Australia; and (below) the BHVHomme fashion store, also in Paris

(mid

dle

) Ph

oto

: A

lpha

Lau /

(bott

om

) Ph

oto

: O

livie

r C

ola

s

CI 45

40 per cent of the construction cost of aconventional treatment plant, and has 5to 10 per cent of the running costs. It needsvirtually no power either, so from a car-bon footprint point of view, it’s very good.”

One worry for hydrologists is that con-taminated water can leak through theclay lining of a constructed wetland.McEntee doesn’t see this as a problem.He says that as organic material settlesout in a wetland, it forms a natural sealin the pores of the clay lining that pre-vents contaminated water seeping out.

McEntee acknowledges that constructedwetlands aren’t flawless though. “Thebiggest downside is the amount of landrequired,” he says. Constructed wetlandsgenerally require more land than conven-tional systems, though they can be devel-oped on most land types and so needn’tnecessarily compete with agriculture forfertile land. Nonetheless, the extra spacerequirements of constructed wetlands canbe justified on the basis that they canprovide amenity value. Many developersinclude water features instead of greenspaces for housing schemes on the basisthat it attracts buyers. A well-designedconstructed wetlands can fulfil this func-tion whilst also reducing environmentalimpacts and providing a home for floraand fauna to thrive.

Constructed wetlands are an example ofthe emerging discipline of ecological en-gineering. But embracing living technolo-gies doesn’t necessarily require such complexsystems; sometimes it’s just a matter ofplanting trees in the right place. In May,Construct Ireland profiled new green-roofedlocal authority offices in Ardee, CountyLouth. The building’s designers alsoplanted trees between the south-facingglazed area of the building and an open

park, creating a natural brise soleil thatprevents glare and overheating in thesummer months.

Smart planting can make an impressivedifference to building performance. Plant-ing deciduous trees on the south side ofa building provides shading during thesummer and allows maximum solar gainin winter. On the north side, evergreentrees will deflect cold winter winds. Ire-land’s mild climate supports an exten-sive array of plants species, with a widerange of seasonalities, enabling archi-tects and designers to create tailoredlandscapes and improve the performanceof a building based on local conditions.

July’s issue of Construct Ireland profiledself-builder Colman McSweeney’s low en-ergy poroton house in Hollywood, CountyWicklow. The house is exposed to two

prevailing winds; existing trees shelter itfrom a northerly wind, but it’s also exposedto a strong south-easterly that emergesfrom the Wicklow gap. During thermalimaging tests, sheltered parts of the ex-ternal envelope were visibily warmerthan exposed elements. McSweeney in-tends to divert the south-easterly windby planting fruit trees. “If we get the mi-croclimate around the building correctwith intelligent planting, it’ll save evenmore energy,” he told Construct Ireland.

Smart landscaping – just like green roofsand walls, and constructed wetlands – is aclever, low energy and natural solution thatcan make our buildings more sustainable,and, quite literally, greener.

For further information on green roofsvisit livingroofs.org

(above) A natural brise soleil shelters the south-face of local authority offices in Ardee, County Louth, from the sun, mitigating glareand overheating; (below) the Noorder Zoo at Emmen, Netherlands, host to 1,500,000 visitors annually. A Living Machine system at thezoo treats 220,000 gallons of wastewater per day, generated by visitors and the maintenance of the housed animals.

(top)

Photo

: G

iita

Ham

mond