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Greening the Way

Greening the Way

Greening the Way

ALSO IN THIS ISSUE

How to Choose the Right page 8Joint Sealant

Project Profile: page 12 Sugar Top Resort

How to Become LEED Certified page 16

ALSO IN THIS ISSUE

How to Choose the Right page 8Joint Sealant

Project Profile: page 12 Sugar Top Resort

How to Become LEED Certified page 16

Vol. 25, No. 2

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3THE APPLICATOR • VOLUME 25, NUMBER 2

Though some may view it as an emergingtrend, green roofs have a long andestablished history. Our Babylonianancestors installed elaborate vegetatedroofs in the terraced structures of theHanging Gardens of Babylon, built around500 B.C., which is considered one of theSeven Wonders of the World. Early 20thcentury installations include New YorkCity’s Rockefeller Center (1930s),Frank Lloyd Wright’s GuggenheimMuseum (1950s) and Madison SquareGarden (1920s).

Like so many technologies, green roofengineering has vastly improved overtime, allowing the industry to migrate tomore modern garden roofs. And in fact,

our condensed, gridlocked cities coulduse it. Viewed from above, most highlypopulated areas bare testament to theimbalanced environment we function inevery day, an environment dominated byconcrete, steel and asphalt with barely ahint of green.

In Europe, particularly Germany, wheregarden roof technology has been inplace for well over 50 years, “nakedroofs” like the black-topped ones towhich we’re accustomed, are viewed asenvironmental, financial and aestheticliabilities due to the burden they placeon municipal storm water systems andenergy resources. Even roofs onindustrial structures in Germany areoften planted with colorful, lowmaintenance sedums.

Reclaiming the FifthElevationIncreasingly here in the United States,that same push to reclaim what somecall the fifth elevation – our roofs – istaking hold. And garden roof technologyis making that easier, with lighter weight

Greening the Way

Greening the Way

Garden roofs, also known asgreen (or eco)

roofs, are an exciting trend in the A/E industry,showing up on projects around the country,including the Seattle Civic Center, Latter-daySaints Conference Center (Salt Lake City), andThe Gap Headquarters (San Bruno, Calif.).

By Wyndham B. Wood

A view of Church Street Station Condominiums (Chicago, Il.) roofline

eco project

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systems that can outlast conventionalblack roofs by decades.

The base of the garden roof is one of themost critical components of a qualitysystem – the waterproofing, ideally aseamless rubberized asphalt waterproofmembrane. Fluid-applied products areapplied directly to the structural substrate,creating a tight bond that has no seams – aconfiguration especially well suited to asaturated environment like a garden roof.

Some manufacturers also offer green roofsystems with modified bitumen, or mod bit,sheet waterproofing, which is installedabove the insulation. Though usedfrequently for blacktop roofs, somequestion the viability of placing so manyseams under a vegetated roof, whichrequires the constant presence of moisture.Any water that seeps through the seamsbetween the mod bit sheets will eventuallyfind its way down to the substrate,producing leaks whose origins are difficultto pinpoint and expensive to repair.

Above the waterproofing, garden roofcomponents vary by manufacturer and byproject. Typically, a root barrier is installed

above the waterproofing to protect itfrom penetration by aggressive roots.Above that, there is a waterdrainage/retention system – an area thathas benefited enormously fromtechnological innovation over the past40 years. More modern garden roofs usefabricated drainage components, whichdrain excess water to drains at 50percent of the weight of the heavy peagravel used in older green roof systems.Because those components also retainwater for the roots to “drink up”, they

also create a more hospitableenvironment for roots to flourish.

This technology accommodates differenttypes of garden roofs, commonly referredto as extensive and intensive. Extensivegarden roofs are low maintenance non-recreational roofs with lower soil depths,usually planted with hardy, colorfulsedums. While most garden roofs benefitfrom irrigation during the first year ofestablishment, extensive roofs often do notrequire long-term irrigation systems.Intensive roofs have deeper soil beds, andcan accommodate a vast range ofvegetation, including large bushes andtrees, which do need regular maintenance.Intensive garden roofs also can be used asrecreational areas – walking parks, golfcourses and soccer fields among them.

System BenefitsWhatever the improvements in technology,however, the inclusion of a garden roof inany given project often boils down to asimple question – how will a vegetated roofbenefit the owner and/or building? Theanswer is simple, though multifaceted.

Although first costs can be higher forgarden roofs, short- and longer-termowners reap the rewards in severaldifferent ways. Early on in a building’s lifecycle, the owner profits from increasedproperty values, and, in the case ofIntensive garden roofs, added useable


The Church Street Station Condominiums Green Roof Project in Chicago, Il.

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Schwab Rehabilitation Hospital and Care Network Green Roof Project schematic.


space. Owners can often chargehigher rents, particularly when agarden roof is accessible to tenants,or visible from interior spaces.

Long-term owners like The Gap, the Cityof Seattle and Schwab also gain fromimproved building performance andlong-term efficiency of the structureoverall. The soil layer of the garden roofperforms several important functions: itinsulates the interior from temperatureextremes, thereby reducing heating andcooling demand; minimizes noisetransmission to create a more peacefuland productive environment; and acts asits own safeguard, providing a thickprotective layer that prevents mechanicaldamage to the waterproofing membranebelow it.

And there are other advantages thatmake garden roofs solid investments,though in less obvious ways. In high-stress environments like corporateheadquarters, for instance, employeescan visit a garden roof to take a breakfrom the daily grind, which mayimprove their health and decreaseemployee absenteeism, saving companiesthousands of dollars annually. Healthcare patients at facilities like theSchwab Rehabilitation Hospital inChicago also may go home earlierthanks, in part, to rooftop “healinggardens”. Those earlier checkout datesenable facilities to take in morepatients each year.

The Urban RoastSome of the best-publicized benefits,however, are those thathave a larger impact onthe municipality andnatural environment thatsurround the structure. Agarden roof directlyaddresses two majorenvironmental issues thatare quickly becominglisted on many cities’ Top

10 concerns –the urban heat island effectand storm water management.

The urban heat island effect, whichdescribes the two to eight degreeFahrenheit rise in ambient temperaturein cities since the early 1940’s, isplaguing cities like Salt Lake City, Atlanta,Los Angeles and many others. Becausehotter cities require more power, mostlyfor cooling, temperature spikes haveadded annual power costs ofapproximately $40 billion. Studies haveattributed these higher temperatures tothe heat-absorbing dark hard surfaces(asphalt paving, blacktop roofs, etc.)that dominate the urban landscape.Computer simulation and otherresearch methods have exposed alucrative cost/benefit ratio to loweringcity temperatures by five degreesFahrenheit; this reduction could resultin annual energy savings of $100million annually. Since urban heatisland patterns are remarkably similarfrom city to city, except for minorvariations in geographical andclimatological features, these figuresare attracting international attention.

Heat is also conducive to smog, whichcan exacerbate such health conditionsas asthma. Because cooler ambienttemperatures lessen smog, reversing theurban heat island effect could also lowerhealth care expenditures. In such citiesas Los Angeles, where smog isdangerously dense, lowering the

ambient urban temperature by fivedegrees Fahrenheit could cut relatedhealth costs by $360 million.

Cooling the cities would also decrease therate at which pollutants (nitrogen oxidesand evaporative organic compounds,specifically) embed into ozone, which isthe principal cause of smog. The overalleffect would be cooler, cleaner air and lessneed for energy-hungry air conditioning.

Minimizing urban heat islands is achievedmost effectively by increasing the amount ofgreen space in cities. Evapotranspiration,defined as the loss of water from the soilboth by evaporation and by transpirationfrom plant growth, can also cool thesurrounding air, which helps lessendemand for cooling (and fossil fuels, as aresult) and mitigate smog. Because roofsare available, open spaces that occupycountless miles of space in any urban core,garden roofs are being heralded as animportant solution to the urban heat islandproblem.

Running Off the RoofCompounding the push toward gardenroofs is another major issue – stormwater management, which, in somecities, is causing potentially irreversibledamage to regional ecosystems. Becausestorm water must be channeled,purified, and detained within enormoussystems, it is a financial and logisticalburden on cities around the globe.

If improperly handled and purified, stormwater contaminated with pollutants fromcity streets and other sources is channeledto natural bodies of water. As thesepollutants build up, local ecosystems areharmed, often seriously. In the PacificNorthwest, for example, salmon havesuffered in recent years because thewaterways they inhabit could barelysupport life.

In areas where the industries like salmonare paramount, the ecosystem’s troublesquickly turn into our own. In the Pacific


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Aerial view of resort.


Northwest, for example, the salmonindustry feeds people, as well as theregional economy. Any contaminatedstorm water that harms the salmon quicklyturns up on the plates, budgets andagendas of businessmen, politicians, citybureaucrats, environmentalists, fishermenand local residents alike.

Garden roofs are a convenient andproductive way to use storm water run-off.Not only does the vegetation need stormwater to sustain its own life, the industry’scurrent water retention/drainagetechnology is designed to store additionalwater for the plants to dip into during driermonths. So, between the soil and othercomponents, some garden roofs canretain as much as 90 percent of the waterthat falls on it. If these types of gardenroofs were installed on large percentagesof any given city’s commercial roofacreage, cities could drastically reducetheir storm water managementexpenditures.

And in fact, forward-thinking cities likePortland, Ore., are getting serious aboutusing garden roofs to solve the storm watermanagement problem. In March 2001,Portland implemented its FAR, or Floor-to-Area ratio, incentive program. FARrewards private developers that includegarden roofs into their buildings withadditional square footage. For instance, aprivate developer who installs a gardenroof on 10 percent to 30 percent of thetotal roof area earns an additional squarefoot of floor area for every square foot ofgarden roof. That ratio improves as thepercentage of space dedicated to a gardenroof increases. Cities like Seattle andChicago are looking at implementingsimilar policies.

LEED™-ing the WayFurther encouraging cities to increase thesquare footage of garden roofs is theUnited States Green Building Council’sLeadership in Energy & EnvironmentalDesign, or LEED™, guidelines. The first

widely recognized definition of “greenbuilding,” LEED assigns credits accordingto specific criteria in areas likeSustainable Sites, Water Efficiency andMaterials & Resources.

Cities like Portland, Seattle, and Vancouver,British Columbia, are looking to LEED as abasis for future green building policy.Because garden roofs that use modernwater drainage/retention technology canqualify for 10+ LEED credits, ownerslooking to achieve LEED certification,whether to meet local policy standards, orfor its marketing value, will benefit fromtheir garden roof through LEED credits aswell.

Educating GreenThough the case for garden roofs is astrong one, there remains a fair amount ofeducation needed to inform owners,contractors, architects and engineers aboutdesigning one. Vegetated roofs requireadditional forethought early in the planningprocess. Factors including those listedbelow should be considered early in thedesign process.

• Design Intent: What is the purpose ofthis garden roof? Will it be pedestrianaccessible? If so, the system will needto be intensive, requiring regularmaintenance and a structure that cansupport the additional weight.

• Waterproofing: Because this is aburied application that won’t beeasy to repair or replace, thewaterproofing membrane shouldhave a proven performance record ingarden roof applications over manyyears. The membrane should last thelife of the building, be fully bonded tothe substrate (no seams for water toseep through), and be installed byexperienced subcontractors. Perhapsmost importantly, the entire system,from waterproofing membranethrough growing medium (engineeredsoil), should be warranted by a single-source manufacturer for at least 10 years.

• Structural Capacity: Althoughgarden roof system weights have beenreduced by 50 percent thanks tolightweight water drainage/retentioncomponents, garden roofs can addweight, so the structure needs to bedesigned for additional loading.

• Water Drainage/Retention: Thisis critical to sustain plant life overtime. The drainage/retention elementshould reproduce basic elements ofnatural ground, drain off excesswater to prevent fungus growth androot rot, retain water for plants to“drink up” over time, and provideadequate aeration for the root zone.


Split-level view of the Greenwich Academy Project in Greenwich, CT.

eco project



• Wind Loading: Like any roof, a gardenroof must be able to withstand windspeeds. While ASTM is currentlydeveloping standards that will addresswind loading for garden roofsspecifically, there are a host of otherstandards that provide guidelines aboutwind loading – among them, FLLGuidelines, Factory Mutual, AmericanNational Standards Institute (ANSI). Anexperienced garden roof manufacturershould also be able to offer wind loadingguidelines.

• Fire Resistance: Like wind loading,fire resistance guidelines are availablefrom individual manufacturers, theUnderwriters Laboratory (UL), theInternational Conference of BuildingOfficials (ICBO) and FLL. Again, anexperienced garden roof manufacturershould have its own guidelines andcertifications.

• Slope: Typical garden roofs systems aredesigned for a maximum slope of twoinches in 12 inches. Extensive systemsmay be able to handle steeper slopes,though battens and restraints may berequired for loose-laid components.Also, steeper garden roofs may requiresoil erosion control measures.

• Detailing: Vegetation-free zones shouldbe installed at all roof flashings, drains,joints, etc. V-F zones are hardscapeareas – typically gravel or architecturalpavers – installed in a strip measuring18 inches wide. Standard protectedmembrane roof drains with extensioncollar and clamping ring can be used inshallower extensive roofs, whileinspection chambers are recommendedfor drains in deeper intensive gardenroofs.

• Maintenance: While extensive systemsrequire minimal maintenance – some aslittle as one annual weeding/watering –intensive systems require regularmaintenance including mowing,weeding, watering and fertilizing.

Dirt: A Four-letter WordDue to the unique nature of theapplication, garden roofs requirespecial growing media – ideally,engineered soil that is tailored to eachspecific application. Ordinary groundsoil – dirt, essentially – is very heavydue to its high clay content. On agarden roof, this material compacts, andholds excessive moisture, preventingaeration at the root zone and creating anenvironment hospitable to fungus androot rot.

Soil engineered for a garden roof ismuch lighter in weight than ordinaryground soil, usually a blend of alightweight mineral like expandedshale, or pumice, sand and organicmatter. The overall mixture shoulddemonstrate a balanced pH, drain welland be capable of holding nutrientsand moisture.

Increasingly, reputable manufacturers arecoming up with their own soil blends,engineered for extensive and intensivegarden roofs in different climates. And,due to the specialization required forgarden roofs, many manufacturers alsonow have soil and plant experts on staff oravailable to A/E professionals planningone of their garden roofs.

Plant SelectionA well-designed garden roof, one that cansustain itself over time, should adhere tothe principles of good ecological design.Appropriate plant selection is an importantpart of this process. Vegetation should bechosen first and foremost for its abilityto mimic the surrounding landscape’sstructure, function and diversity;withstand the harsh conditions of a roof;and thrive in the local climate. Gardenroof vegetation should be sustainable,not reliant on fertilizers, irrigation ormaintenance.

Plant diversity is important to a gardenroof’s long-term potential. To maximizeseasonality, early and late flowering

species should be planted, along withannuals and long-lived perennials.Mixing in shallow-rooted wildflowerswith deeper fibrous-rooted grass-likevegetation helps to encourage long-termplant viability.

Using these general guidelines, specificplant choices should be determined byseveral factors. Garden roof vegetationneeds to be resistant to direct radiation,drought, frost and strong windconditions. Often, native plant palettesoffer the most favorable options, speciesthat are regenerative and self-sustainingin the local climate.

The Future Is Looking GreenCity workers in Seattle, hospital patients inChicago, boarding school students andteachers in Greenwich, Conn., -- these arejust a few of the groups benefiting fromthe thousands of garden roofs beinginstalled on commercial structuresacross the country. And many more willfeel the positive effects in the years tocome, as garden roofs assume anincreasingly larger place on ourbuildings, in our construction documentsand city policies. It’s an excitingmovement, one that will help clean ourair and water, improve our quality of lifeand reintroduce some much-neededbalance into our cityscapes. ■

Wyndham B. Wood has worked in thesustainable building industry for thepast seven years, focusing on gardenroofs and the LEED(TM) green ratingsystem. Among her other publishedpieces on the topic is "Cool Roofs,"printed in Earthpledge's SustainableArchitecture White Papers.

eco project


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