Up on the Roof

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A clothing retail outlet at the Brussels end of the A3 motorway might not be the first place you'd look for environmental inspiration. Yet the green roof on the Caméléon building in Woluwe-Saint-Lambert is part of a revolution that's quietly gathering pace in today's ever-more crowded cities.

From the air you might easily mistake it for a large suburban garden or a little patch of parkland. Indeed, in one way it is exactly that, several storeys up: 2,000m2 of fertile, well-drained and thoughtfully cultivated ground, creating an unexpected haven for plants, birds and insect life. You might even spot a couple of the city's beekeepers up there, tending the rooftop's three impressively productive hives.

Green roofs may be unusual, but they are neither wacky nor whimsical. Nor do their benefits end with biodiversity. The architects' brief for the Caméléon building, which went up in 2009 and won a string of environmental awards, required the highest sustainability standards in every aspect. So they opted for a green roof as much for its insulation properties as for the natural habitat it provides.

Green roofs are great for reducing heat energy loss. They keep the inside naturally cooler in summer - and quieter too. The layers of vegetation, soil or planting and (recycled) substrate also shield the waterproof roof membrane from damaging exposure to sun, wind and weather.

What's more, with water the central theme of Green Week in Brussels this month (22-25 May), it's well worth emphasising how highly green roofs score on the water front, even if you're not actually harvesting the rain to help meet your building's needs.

One of their biggest attractions for urban planners is the green roof's ability to soak up a heavy downpour, slowing and reducing the run-off to over-burdened storm drains. In this way they can do a lot to mitigate the risk of flash flooding associated with the spread of 'hard catchment' in built-up areas. In London for example, it has been suggested that the need for a super-sewer could be much reduced by integrating it with green infrastructure, and Thames Water and the Greater London Authority are running a joint project to quantify the benefits.

In another European capital, Budapest, the same considerations loomed large in the decision to create one of the largest green roofs in existence. Spanning nearly 20,000m2 - as big as three football pitches - and covering the city's wastewater treatment plant, it was installed in just a few weeks last summer at a cost of €0.5m.

The speedy construction was achieved by using a massively scaled-up version of the 'Diadem' system, developed to offer green roofing solutions at any size including small home extensions. In this giant Budapest application, a mix of intensive and extensive planting has been used to grow a wide range of vegetation, from trees and shrubs down to grasses and herbs. Particularly welcome is these plants' ability to filter out ambient urban pollutants which otherwise get carried down into the groundwater when rain runs off hard roofs and other surfaces.

For all the practical environmental benefits of green roofs, which also include absorbing carbon dioxide and reducing the so-called 'urban heat island effect', there's another and simpler reason that we're starting to fall in love with them: just because they can look so fabulous, both from afar and up close.

A little green roof on a garden shed can blend in beautifully, while evoking romantic notions of quaint turf-roofed country cottages. As a well-planned public amenity, an extensive green roof like the park and tree-lined avenues atop the University of Warsaw's ibrary can provide an extra little oasis of peace amid the pressures of city living.

And for 'statement' architectural designs that catch the zeitgeist, buildings like New York's Via Verde (green way) are surely hard to beat. The press and public accolades for Via Verde, the kind that a prestigious Manhattan development might long for, are all the more astonishing when you realise that this beacon for sustainable urban renewal is actually a social housing project in the South Bronx.

Designed by Dattner and Grimshaw architects, the building started construction in mid-2010 and has welcomed its first tenants. At the time of writing, it was still possible to buy into one of the 75 affordably priced cooperative units there, though the 151 low-income rental units were all taken straight away.

In Europe, Germany and Scandinavia pretty well lead the field in this fast-growing contribution to more sustainable cities.

In Germany, the early establishment of a technical standard for green roofs has emboldened the construction industry to roll them out with growing confidence. Encouraged by planning policies, they are now a feature of one new building in 10. Copenhagen, which will host an international green roof congress later this year, might almost be considered its headquarters.

The 1700m2 of living, breathing greenery on two long, sweeping slopes of roof at the 8 House in the Copenhagen district of Oerestad,for instance, has recently been designated the best green roof in Scandinavia. A mixed development of offices and 540 dwellings, it also won the housing category in the 2011 World Architecture Festival Awards.

But elsewhere in the city, an 80-unit housing development known as Mountain Dwellings illustrates a rather different, yet equally attractive, approach. Each family here gets their own private back garden in the form of a green roof over the unit below, thereby combining city living with that backyard feel of suburban life.

As these and other award-winning buildings boost the profile of green roofs, their environmental, social and economic credentials are alerting a wider audience that they can be a smart solution even for the most modest projects. New build or retrofit, sheds, home extensions, houses, schools and all kinds of public and commercial buildings are starting to reap what they have sown.

FR 
Sur le toit

Réduction de la déperdition de chaleur l'hiver, garantie de fraîcheur l'été et bénéfices environnementaux, les villes du monde s'engagent dans l'architecture verte. Par Roger East

Un outlet de mode et de design, à la sortie bruxelloise de l'autoroute A3, n'est pas a priori le lieu où on penserait trouver une inspiration environnementale. Et pourtant, le toit végétalisé du bâtiment de Caméléon, à Woluwe-Saint-Lambert, fait partie de cette révolution qui gagne du terrain dans nos villes toujours plus peuplées. Sur 2.000 mètres carrés, plusieurs étages de terre fertile créent un havre inattendu pour les plantes, les oiseaux et les insectes. On y trouve même trois ruches !

Inhabituelles, les toitures végétales ne sont pas pour autant farfelues. Et leurs bénéfices ne s'arrêtent pas à la biodiversité. Dans le cas du bâtiment de Caméléon (2009), récompensé de plusieurs awards, le briefing des architectes requérait les plus hauts standards de durabilité. Ils ont donc opté pour un toit végétalisé, tant pour ses propriétés isolantes que pour son habitat naturel.

Ces toits sont une excellente solution pour réduire la perte de chaleur et assurer un intérieur naturellement frais l'été. Les couches de végétation protègent également la membrane imperméable du toit d'une exposition dommageable au soleil, au vent et aux effets climatiques.

De plus, alors que l'eau est le thème central de la Green Week qui se tiendra à Bruxelles ce mois-ci (24-27 mai), cela vaut la peine d'insister sur l'apport positif des toits verts en la matière. L'un de leurs principaux attraits est leur capacité à absorber les fortes averses, et donc limitant le risque d'inondations subites, souvent associées aux zones urbanisées.

Enfin, outre tous les bénéfices environnementaux de ces toits végétalisés - y compris l'absorption du dioxyde de carbone et la réduction de « l'effet d'ilôt de chaleur urbain », il y a encore une autre raison à leur développement, bien plus simple : nous sommes tout bonnement en train d'en tomber amoureux, ces toits peuvent avoir un look fabuleux, de loin comme de près. Du projet d'habitations sociales Via Verde dans le district du Bronx à New York à la 8 House de Copenhague, en passant par les travaux publics de traitement de l'eau à Budapest, aux quatre coins du monde, les villes commencent à en récolter les fruits.

NL 
Op het dak

Warmteverlies beperken in de winter, het hoofd koel houden in de zomer en flora en fauna een handje toesteken: het succesverhaal van de daktuinen. Door Roger East

Milieu-inspiratie zoekt u misschien niet in een kledingzaak, maar het groene dak van het Caméléon-gebouw (Sint-Lambrechts-Woluwe, 2009) maakt deel uit van een revolutie die de steden inpalmt. Zo'n 2.000 vierkante meter aan vruchtbare, zorgvuldig gedraineerde en bewerkte grond is een thuishaven voor planten, vogels en insecten, en voor drie zeer productieve bijenkorven.

Groene daken zijn zeker niet het resultaat van een bevlieging en het gaat om meer dan alleen maar biodiversiteit. De architect wou met het Caméléon-gebouw, dat ondertussen een hele resem aan milieuprijzen in de wacht sleepte, de hoogste duurzaamheidsnormen naleven. En dus koos hij voor een groen dak - als isolatiemiddel, maar ook als natuurlijk habitat.

Groene daken gaan warmteverlies ongelofelijk goed tegen en in de zomer houden ze het interieur frisser. Om van de geluidsisolatie nog maar te zwijgen. De verschillende lagen vegetatie, bodem en substraat vormen ook een waterdicht membraan dat beschermt tegen zon, wind en guur weer.

Nu "water" tijdens de Groene Week in Brussel (24-27 mei) het kernthema is, mag gezegd worden hoe goed groene daken op dat vlak scoren. Een van dé voordelen is dat ze stortbuien goed absorberen en de afvloeiing naar de overbelaste regenwaterafvoer vertragen en beperken.

Daktuinen hebben veel milieuvoordelen - absorptie van koolstofdioxide, vermindering van het zogenaamde "stedelijk hitte-eilandeffect", ... - maar ze zien er vaak ook gewoon schitterend uit. Wereldwijd sluiten steden bij het concept aan: Via Verde, sociale huisvesting in de New Yorkse Bronx, 8 House in Kopenhagen, een waterbehandelingsproject in Boedapest, ...

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