ISSUE 2/2007  V O L U M E 2 4  N U M B E R 2

Journal of architectural technology published by Hoffmann Architects, Inc., specialists in the rehabilitation of building exteriors. Reroofing Green

Richard P. Kadlubowski, AIA

Seen from the air, the contempo- and up. Adding this type of green rary urban landscape is changing. No to an existing structure can require sig- longer solid swathes of grey and black, nificant restructuring or augmentation of cities are ever more dotted with lively the roof deck, so a thorough structural patches of green—the vibrant foliage analysis is imperative. of roof and plaza plantings. And these A lower-maintenance, lower-cost green roofs aren’t always what you alternative is the extensive green roof. might expect. Not just for opulent Here, plants are selected for their penthouse gardens or costly environ- resistance to high heat and drought, as mental experiments, landscaped roofs well as for their shallow root systems and plazas adorn structures rang- and water retention. Sedum and na- ing from public housing projects to tive grasses and flowers are commonly city halls to corporate headquarters, used options. With limited access and and they’re gaining momentum. In shallow growing media, these roofs the current drive to reduce energy add fully saturated weights of closer to consumption and protect against rising 30-50 lbs/sq. ft.—still significantly more temperatures, even the most modest than a standard roof (usually 1-15 lbs/ green roofing projects stand out as sq. ft.), but more manageable than an real and lasting solutions. Is your roof intensive roof garden. Planting media ready? Here’s a look at some options with high inorganic content (70-80%) and considerations. and low plant heights contribute to the reduced loading. And unlike a tra- What is a Green Roof? ditional garden, extensive green roofs When we picture a traditional garden can have slopes of up to 30°; steeper on a roof, with grasses, flowers, shrubs, slopes can be achieved using grids or or trees, what we are likely imagining is lathes to hold the plants and growing an intensive green roof. These gardens matter in place. Gardens atop buildings, are designed as usable space and must While extensive green roofs may offer among the first and most well-known green therefore accommodate significant a more practical option for retrofit roofs in City. amounts of foot traffic beyond that of projects than do intensive roof gar- maintenance crews. Growing media dens, a qualified design team must first tend to be deep (a foot or more) and assess whether an existing structure dense in organic material (45-50%), with can be safely redesigned to withstand fully saturated weights of 80-120 lbs/sq. ft. the additional load.

Richard P. Kadlubowski, AIA, directs Hoffmann Architects, Inc.’s Washington, DC office. As Vice President and Senior Architect, he oversees a wide range of roofing projects and is experienced at evaluating, maintaining, and rehabilitating all elements of the building envelope. Hoffmann Architects, Inc. is a member of the U.S. Green Building Council. JOURNAL

rating water, cooling the surrounding Typical Standard Green Roof Assemblies air. That translates into as much as 25% reduction in summertime cooling costs. If more cities were covered with green, we would see less power B grid loading and lower summertime power prices; currently, a full 1/6 of US energy is used to cool buildings. In the winter, green roofs provide added C A insulation with 18% less heat loss than with conventional roofing. C

D D Noise Reduction. Plants, growing matter, E E F and trapped air and moisture in soil are G G excellent insulators, not just thermally, H H I I but acoustically, too. Some studies have J J shown that green roofs can reduce A. Sedum, herbs, alpine plants F. Moisture Mat (as required) outdoor noise heard inside the building B. Annuals, perennials, shrubs, woody plants and trees G. Insulation by 40 decibels or more, depending on C. Planting media (extensive, 3”-6”; intensive, 6”-10”+) H Root Barrier the depth and nature of the substrate. D. Filter I. Membrane E. Drain (may be filled with lightweight aggregate) J. Roof Deck In busy city centers or near traffic, machinery, or airplanes, buildings with

ADAPTED FROM AMERICAN HYDROTECH, INC. WITH PERMISSION INC. AMERICAN HYDROTECH, FROM ADAPTED green roofing offer their occupants a Why a Green Roof? options), don’t rule it out. Green respite from noise pollution. When faced with a deteriorating roof, roofs also last twice as long as most Preservation of Roof Waterproofing. most owners and managers have standard roofs, which require replace- Bare roofing membranes, which are three prime concerns when assessing ment every 15-20 years. Some green subjected to extremes of temperature re-roofing options: cost, longevity, and roofs in Germany, where green roof and intense direct sunlight, dete- performance. Each re-roofing project technology was pioneered, have lasted riorate more quickly than do those is unique, with special considerations 40 years without needing replacement. protected by plantings. Not only do depending on type of construction, And the long-term benefits are many. plants moderate the air temperature, location, climate, and building use. A Some to consider: their leaves disperse sunlight which qualified design professional can assess Energy Savings. On a 95°F day, the would otherwise impinge directly on individual requirements and help build- temperature of a conventional roof waterproofing materials. This layer of ing owners or managers to select the can be about 158°F. On a green roof, protection adds up to longer mate- right solution for their re-roofing needs. the temperature would be closer to rial lifespan—and reduced membrane maintenance and replacement costs. While the initial cost of installing a 77°F. Why? In the process of evapo- green roof may seem prohibitive (it transpiration, plants use heat energy Water Runoff Management. The job of can be twice as much as conventional from their surroundings when evapo- a conventional roof in a rainstorm is

Green Roof History Modern green roofs, composed of layers of waterproofing membranes, root 1961 barriers, growing media, and vegetation, were popularized relatively recently, beginning in Germany in the 1960s. Still, the concept is not new. The Hanging Dr. Reinhard Bornkamm of Berlin, Gardens of Babylon were built around 600 BC, and Scandinavian countries Germany’s Free University publishes his groundbreaking work on green roofs. have traditionally covered their pitched roofs with grass since the time of the Vikings. The following timeline marks key moments in the contemporary movement toward greening America’s roof landscapes:

ALL PHOTOS IN TIMELINE COURTESY AMERICAN HYDROTECH, INC.

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to drain water as quickly as possible, ing appeal of a standout green roof, projects through grants, credits, and as any pooled water can mean leaks. which can increase property values fee waivers. When a city is hit with significant significantly. In some areas, notably Chicago and rainfall, all the buildings, not to men- Even green roofs that aren’t designed Washington, DC, building owners can tion roads and sidewalks, are unload- for recreation enhance the local envi- take advantage of tax breaks and fund- ing water at once; sometimes, enough ronment by becoming home to local ing that may help offset the higher initial to overwhelm the city’s sewer system. birds and insects. Some demonstra- costs associated with a green roofing This can lead to backups and even raw tion projects and designs have featured project. New York, Oregon, California, sewage dumping in the waterways. restored local habitats in areas where and Maryland have also implemented Depending on the plants and growing natural ecosystems are dwindling. incentive programs, and other states medium used, green roofs can retain These roofscapes attract the attention and cities are following suit. As part of up to 90% of rainwater. Any runoff is not only of wildlife, but of the press and the investigative phase of a green roof then released slowly as it’s filtered by others in the community. project, a design professional can help the plants, reducing stress on sewer determine which, if any, of these cost systems during peak flow periods. savings apply to your building. Moderated Heat Island Effect. The “Heat Island Effect” occurs when “While green roofs Structural Concerns asphalt, tar, and concrete trap heat and While green roofs offer real ben- raise the temperature of dense urban offer real benefits, efits, they also present some special areas with respect to the surround- concerns. Water, plants, growing media, ing rural countryside — as much as they also present planters, root barriers, and other mate- 10-15°F. This rising bubble of hot air rials add significant load to a building’s over cities creates artificial air currents some special structural support, even in a relatively that then contribute to smog, ozone, lightweight extensive roof garden. and dust. Green roofs’ heat-absorbing concerns.” properties not only benefit the owner Roof Loading and occupants with reduced energy When properly designed and con- costs, they also offset the Heat Island Government Incentives. Rising energy structed, roofs, as well as plazas and Effect and provide a cooler microcli- demands and concerns about smog terraces, should be capable of carrying mate for the surrounding community. and other pollution have led many lo- the required dead and live loads. Health and Habitat. Occupants and cal governments to offer incentives for The dead load is the weight of all those in the surrounding community sustainable building methods, includ- materials of construction incorporated will enjoy not only the health benefit ing green roofing systems. States and into the building, which includes walls, of improved air and water quality municipalities benefit greatly from floors, roofs, ceilings, stairways, built-in afforded by green design, but also the improved storm water manage- partitions, finishes, cladding, and other the aesthetic advantage of a greener ment, reduced energy demands, and similarly integrated architectural and landscape. And building owners and mitigated pollution provided by green structural components, as well as fixed managers appreciate the eye-catch- roofs, and often encourage such service equipment. With respect to

1971 1975

Gerda Gollwitzer and Werner Wirsing, The Landscape Research, Development German landscape architects, pioneer & Construction Society is founded modern green roof design, backed by in Mainz, Germany and establishes study and testing of materials, in their green roof standards. book, Roof Areas Inhabited, Viable, and Covered by Vegetation. Schwab Rehabilitation Hospital, Chicago, IL

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for construction loads and environ- would need to be transferred to the mental loads, such as those caused bearing points (generally columns by wind, rain, or snow. Depending and walls), and then to every level on the building’s geographic location, below, down to the footings. Provid- the design may need to account for ing additional bracing from only the earthquake or flood loading as well. floor below would not provide true Roofs and plazas in northern climates structural support to the new load. experience greater snow loads than do Green roof components such as those in the south, and winds in coastal the drainage, water retention mats, regions would impart more load than and soil must be considered at their those further inland. Building configu- saturated weights in order to calcu- ration, as well as environment, must be late the additional loading. Increased taken into account; whether the roof foot traffic and irrigation/maintenance is flat, sloped, open, or congested with equipment must also be evaluated, as numerous projections also affects snow well as changes in wind, snow, or rain COURTESY LIVEROOF, LLC LIVEROOF, COURTESY and wind loading. loading in the new design. In a modular system, such as LiveRoof’s, Most structures were designed to pictured above, plants are grown to maturity Methods for strengthening decks vary by support the required dead and live offsite in recycled plastic modules, which type of construction, configuration, and are then set tightly together for a uniform loads for their building configuration, environment. Steel decks may require appearance. location, and function—but little more. additional support from below in the To retrofit an existing roof deck with form of additional beams or trusses, growing media, plants, and containers, whereas concrete decks may need roofs and plazas, the dead load also augmentation of the structure may new connection supports at columns accounts for waterproofing systems be necessary to accommodate the or augmentation with a steel support and associated coverings (e.g. ballast, additional loads and prevent serious section. A qualified architect or engineer pavers), and may include planters and structural failure. can determine how much additional benches if they are part of the original support the green roof will need, as well design. How to Strengthen an Existing Deck as the most efficient, cost-effective, and In contrast, live loads fluctuate with Beginning with a structural evaluation secure way to direct the increased load building use, and are generated during is critical prior to undertaking any down to the base of the building. the life of a structure by people and project that would exceed current moveable objects. A roof that sees design loads. Once the existing Waterproofing Concerns only maintenance crews and equip- building’s capacity and the new load Unlike a traditional roof, a green ment would have a considerably requirements have been determined, roof needs some degree of moisture smaller live load than would one with additional structural support can be saturation in order for plants to thrive. significant foot traffic. tailored to the type of construction. The goal of waterproofing in either In addition to dead and live loads, the For all types of decks, the additional case is to keep water out of occupied building design must also accommodate loads for a rooftop or terrace garden spaces; on a green roof, however, water

1998 1999 The Business Week/Architectural Record Award applauds environmentally sound Green Roofs for Healthy Cities design at Gap Inc.’s grass-covered California headquarters, built in 1997. is formed in Toronto, Canada After observing green roofs in Germany, Chicago Mayor Richard M. Daley to promote construction subsidizes green-roof projects and research with municipal funds. of green roofs in North America. The U.S. Green Building Council creates the LEED rating system (Leadership in Energy and Environmental Design), which offers points for green roofs.

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does not channel immediately to branes on the market for green roof Fluid-applied systems are similar to drains, but instead filters through the applications. These may be organized built-up systems in that reinforcing planting media. In a well-balanced sys- into three basic categories: sheet (in- and binders are used to produce the tem, plantings and soil absorb moisture cludes single-plys, thermal plastics, and final membrane. However, with the before it can reach the roofing mem- rubber membranes), built-up (includes liquid-applied systems, the binder/ brane, while any excess water drains MBR and typical BUR systems), and membrane fluid itself is the primary without over-saturating the system. fluid-applied (hot or cold, asphaltic, waterproofing. Installation involves Still, the level of moisture in a vegetat- acrylic, or epoxy). application of the liquid membrane ed roof covering presents challenges, Sheet systems have sheets of mem- to the deck, then addition of reinforc- in that the constant presence of water brane that are adhered to the deck, ing, to increase strength and puncture can be a potential source of leaks. but which then require some type of resistance, while the layer is still wet. In a green roof project, as with plazas seaming process to bind the pieces A second layer of fluid is then applied and terraces, the roofing membrane together. Depending on the mate- over the first. When the installation is buried below tons of plantings, soil, rial, the seams may be glued, taped, is complete, a monolithic, no-seam drainage media, pavers, and other or welded. The quality of the seam is membrane is achieved. aesthetic elements, making it extremely dependent on the applicator. Making the Right Choice difficult, costly, and time-consuming to Most sheet membranes have rein- locate the source of a leak and correct forcing to resist puncture, but be- Some factors that enter into the decision: it. In all roofing jobs, waterproofing is a cause sheet membranes typically have • Strength. Although protection mats critical component, but it is even more no self-healing properties, any tears and root barriers keep plants from so with a green roof, where there is that do occur remain until repaired. impinging on the waterproofing little room for error in membrane and Adhesion to the deck prevents mois- system, reinforced membranes offer system choice or installation. ture from traveling, localizing leaks an added degree of impenetrability. and minimizing costly and difficult The keys to success include specify- • Resilience. A waterproofing system searches for the water infiltration ing the right roofing system, selecting without seams would eliminate source. a capable contractor, and having a initial points of water entry. quality control representative on site Built-up systems, as the name implies, • Ease of repair. Waterproofing that to confirm that construction adheres are installed by laying down multiple is fully bonded to the deck would to the details and specifications. Once smaller sheets of material and bonding the roofing system is in place, exten- them in layers of hot asphalt, coal-tar keep any moisture that does pen- sive flood testing should be completed pitch, or cold adhesives. The multiple etrate the system from travelling to confirm the membrane’s integrity layers provide a level of redundancy beneath the membrane. It’s easier prior to adding the overburden and not found in monolithic systems, and to fix a leak if you can readily find its green components. they offer both puncture resistance source. and self-sealing properties. Applying • Self-healing properties. Due to the flow Waterproofing Systems the system directly to the deck helps characteristics of the material, bitumen- Just as with traditional roofs, there are to keep any leaks that do occur local- based systems can often recover from many choices of waterproofing mem- ized for easier repair. small punctures without intervention.

2001 2003 Atlanta installs the first municipally- The country’s first owned green roof in the Southeast municipal green roof on its city hall. is installed on Chicago’s city hall. Ford’s assembly plant in Michigan adds one of the world’s largest green roofs, now a tourist attraction. LDS Assembly Hall, Salt Lake City, UT

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A good choice in many applications will provide years of hassle-free, low- assembly. An advantage of the former would therefore be monolithic, fluid- cost roof maintenance, while plantings is that the roof will be “green” im- applied, bitumen-based waterproofing protect the membrane—rather than mediately upon installation. However, membranes. These resilient, self-heal- cover its problems. these systems are generally only for ing systems balance ease of applica- extensive roof gardens; larger plantings tion, durability, and compatibility with Selecting a Planting System (such as trees and shrubs), those that overlying planting matter. Each roof is require more maintenance (flowers System Components different, however, so an individualized and grass), or those accessed by the assessment of existing construction, in In a typical traditional roof assembly, public may necessitate grown-in-place, light of project goals, is essential. there are generally four layers: sub- multi-layer systems. strate (roof deck), insulation, membrane, Before choosing a planting system, Costs and Concerns and ballast or coating. Green roofs may consider the deck slope and existing have nine or more layers, including: Green roof projects can be expensive, electrical and water infrastructure. and it can be tempting to cut costs in • Substrate (deck) Some green roof designs may accom- this phase of the project by opting for a • Insulation modate a greater range of slopes and low-bid contractor or neglecting quality still achieve proper drainage. Irriga- control oversight. However, choosing • Waterproofing membrane • Protection board or fabric tion and other maintenance systems the right roofing system is not enough. will also need to be considered at • Root barrier Proper methodology and detailing, the time of installation. Options for a particularly along the perimeter and • Drainage media (drainage board or retrofit green roof project may be lim- at penetrations, save money in the gravel) ited by the building’s structural loading long-term by preventing waterproof- • Moisture retention material capacity, levels of sun or wind expo- ing system failure down the road. An • Growth media (soil) sure, existing waterproofing system, experienced design professional can or other intrinsic factors, as well as by help building owners and managers • Plantings budgetary and logistical constraints. select the right contractor, oversee the Depending on the type of green roof, roofing installation, and provide qual- extensive or intensive, additional or Vegetation and Design ity control testing to see the project fewer layers may be required. The se- Plant selection depends on a variety of through to a successful completion. quence of the assembly may also differ, factors. Some to consider: as, for example, when the membrane Cost savings can be realized on many is applied directly to the substrate, • Climate elements of a green roofing project. with insulation atop the membrane. Cutting corners on the waterproofing • Sun and wind exposure process, however, may mean an ex- Green roof systems may be modular, • Type and depth of growing medium pensive and disruptive repair project in with drainage layer, filter, and growing • Loading capacity the near future, when planters, pavers, media prepared off-site in move- • Height and slope of the roof deck soil, and vegetation must be removed able, interlocking containers. In other • Maintenance expectations to remedy a water infiltration problem cases, each component of the system that might have been prevented. Wa- is installed separately, and plantings • Irrigation terproofing prudently from the onset are cultivated in the completed roof • Aesthetics

2004 2008 Scheduled opening of the new Millennium Park in Chicago California Academy of Sciences becomes an immense green roof, building, which will include a 2.5 acre extending 24.5 acres green roof of native vegetation, over underground parking garages. designed as a habitat for indigenous species. Mashantucket Pequot Museum, Mashantucket, CT

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While gardens of grass and trees are Exposure to Traffic. Like plazas and possible on a rooftop, these necessi- terraces, intensive green roofs see sig- tate constant upkeep, as well as costly nificant foot traffic, creating the threat irrigation systems. Other roof gardens of potential damage to waterproofing cultivate minimal-maintenance native membranes, even if they are protected. plants, which mimic local habitats and can become home to birds, butterflies, Safety Concerns. Traditional roofs and insects. Some roofs or ter- are exposed to relatively little traffic, races have even been used for urban except from contractors and main- agriculture, providing fresh produce tenance personnel experienced with to restaurant and hotel guests or roof safety. On a green roof used by residents inside the building. the public, however, tripping hazards and other sources of potential injury A popular type of vegetation for must be vigilantly monitored. Even ex- extensive roof gardens is sedum, a tensive green roofs present additional low-maintenance plant that is heat safety concerns, as maintenance work- and drought resistant—important ers must negotiate narrower walkways qualities in the baking temperatures and, depending on the system, irriga- of a rooftop. Its shallow root system tion and other equipment. means less depth of growing media, yet it holds a high percentage of Increased Loading. People, pavers, rainwater. More absorption means planters, growing media, and mainte- less runoff, which reduces the burden nance equipment put stresses on the on drainage systems. Sedum is also building beyond those in a typical roof popular because it is so easy to grow installation. Green roofs need special and maintain; although initial irrigation consideration of load-bearing capacity. is necessary to establish the plantings, Waterproofing Issues. Vegetation and once the system is in place, it is es- ARCHITECT.) ASSOCIATES/LANDSCAPE OF RICHARD BURCK STEPHEN LEE (COURTESY PHOTO: sentially self-sustaining. growth systems create unique water- This extensive green roof assembly above proofing problems and affect drainage. a one-story parking garage at Harvard Uni- Challenges of Green Roof Projects Gaining access to the waterproofing versity places succulents, sedums, and della layer is much more complicated and spirna plantings over a fluid-applied, direct- Green roofs and, similarly, terraces and expensive on a green roof, because bonded, monolithic membrane. plazas over occupied spaces, present the entire planting system must first be special rehabilitation issues that are removed. Although top quality perfor- waterproofing membrane. In a dense generally not concerns in other hori- mance is required in all horizontal wa- urban setting or in an occupied build- zontal waterproofing projects, such as terproofing projects, green roofs require ing, noise and dust must be minimized parking decks or traditional roofs. A a particularly conservative approach. sampling: over a considerable period of time, Flashing Design. While flashing is a generating costs and logistical chal- Aesthetic Requirements. A green potential weak point in any waterproof- lenges not encountered in traditional roof becomes part of the structure’s ing job, it presents added concerns in roof rehabilitations. For this reason, aesthetic character, acting as a “fifth a green roof project, where it is often it’s especially critical to waterproof façade” that’s as visible to the public expected to occur below the vegetation a green roof properly at the time of as any other building face. While level or to be hidden in some other way. installation. most green roofs are more ecologi- cal powerhouse than garden, they still Debris Removal. To rehabilitate a green Plantings. Selecting and maintaining draw the public eye and so demand roof, considerably more material must plantings and appropriate growing me- attention to detail. This is true with be removed from the site than in a dia that can withstand rooftop condi- any green roof, but it is especially true typical roofing project. Plants and tions without exceeding the structural of those open to more than mainte- growing media, planters, and pavers design load is a critical component of nance traffic. must all be removed to access the the “greening” process. Should roof

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off management and reduced JOURNAL is a publication of heat island effect. Hoffmann Architects, Inc., specialists in Corporations the rehabilitation of building exteriors. The firm’s work includes investigative and municipalities and rehabilitative architecture and that “go green” engineering services for the analysis have been cited and resolution of problems within as leaders in the roofs, facades, glazing, and structural conservation systems of existing buildings, plazas, movement, and terraces and parking garages. their buildings Please send news, technical information, have received address changes or requests for free much attention in subscriptions to Editor, Hoffmann Architects JOURNAL, 2321 Whitney COURTESY LIVEROOF, LLC LIVEROOF, COURTESY the press. With Laying sedum on an extensive green roof. the drive to Avenue, Hamden, CT 06518. reduce energy For information on the services repairs be necessary, plantings may consumption, decrease global warming, offered by Hoffmann Architects, Inc., need to be restored or replaced after and protect our air and waterways from contact our Marketing Coordinator at rehabilitation work is complete. pollution, building practices have looked 800-239-6665 or: to innovative designs to reduce environ- 2321 Whitney Avenue Costs. Green roofs can be more than mental impact. Hamden, CT 06518 double the price of traditional roofs 203-239-6660 to install and rehabilitate. However, Before embarking on a green roofing energy savings and waterproofing retrofit project, consult an experi- 500 Fifth Avenue, Suite 830 enced design professional to assess New York, NY 10110 membrane protection, in addition to 212-789-9915 government incentives, can help to the structural capacity of your building, offset some of the additional expense. and to evaluate the waterproofing and 1001 Avenue NW, Suite 825 planting system options. A green roof Washington, DC 20036 is a significant expense, so a properly 202-530-1100 The View from the Top suited design and proficient installation For more information on the topics A green roof provides benefits on many are critical to the long-term success of discussed in this article, visit us on the levels: economic, including reduced the project. With the right guidance, a web at www.hoffarch.com or contact heating and cooling costs and extended green roof can be an eye-catching asset us at [email protected]. roofing membrane lifespan; social, such with great returns on the initial invest- Editor: Alison Hoffmann as improved health and surroundings; ment, both for the individual building Production: Margaret Bailey and environmental, including water run- owner and for the community.

Hoffmann Architects, Inc. 2321 Whitney Avenue Hamden, CT 06518

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