ISSUE 2/2009  V O L U M E 2 6  N U M B E R 2

Journal of architectural technology published by Hoffmann Architects, Inc., specialists in the rehabilitation of building exteriors. Fundamentals of Plaza Design

Craig A. Hargrove, AIA LEED AP and Stephanie L. Dillon, Assoc. AIA

A plaza can be an attractive ame- or terrace rehabilitation can provide nity, especially in an urban area where excellent return on investment. open space is at a premium. But when age, deferred maintenance, de- Plaza Use and Configuration sign defects, or faulty construction lead When considering options for plaza to unsightly weed growth and pooling or terrace design, an architect or water, dangerous tripping hazards and engineer will first assess the function ice buildup, or costly maintenance de- and composition of the space. A plaza mands, it might be prudent to protect over which vehicles routinely drive that amenity by rehabilitating it. demands a different type of assembly The question is, “how?” (And, rea- than does a terrace that sees sonably, “how much?”) The answer only maintenance foot traffic. depends on the type of system that’s Similarly, a private terrace for the in place, the type you opt to install, exclusive use of building tenants has the use of the plaza space, and the different design considerations than complexity and requirements of plant- does a plaza classified as “privately ers, stairs, fountains, seating, and other owned public space” or one in a busy features. To begin, a team of architects campus setting. Access, circulation, and/or engineers should evaluate the furniture, decorative elements, and existing plaza or terrace and help es- plantings must be coordinated to Plaza investigation by an experienced tablish a realistic rehabilitation budget. facilitate intended usage. Paving architect or engineer uncovers the causes of Then, the design team should guide assemblies and materials, as well as water damage or deterioration. you in balancing project variables to any waterproofing systems, are thus achieve the desired look while meet- dictated not only by the form of the ing cost objectives. plaza or terrace space, but also by its A well-designed plaza or terrace not function. Historic planning regulations only reduces upkeep costs, it also may place further restrictions on attracts tenants, increases property surfacing options. value, and enhances outdoor space. With reductions in energy and main- Types of Paving Assemblies tenance expenses afforded by “green” The surfacing system needs to ac- design principles and sophisticated commodate the volume and type water movement strategies, plaza of anticipated traffic, while meeting

Craig A. Hargrove, AIA LEED AP directs Hoffmann Architects, Inc.’s City office. As Senior Vice President and Director, Architecture, he is responsible for the integrity, coordination, and oversight of diverse plaza and terrace rehabilitation projects. Stephanie L. Dillon, Assoc. AIA, Project Coordinator, has experience in all phases of plaza evaluation, waterproofing, design, and construction. JOURNAL

Plazas Over Occupied Space

Waterproofing is the central concern for a terrace or plaza that is also a roof.

The membrane. Once the waterproofing has been installed on a plaza or terrace, it is buried beneath tons of overburden, making it virtually impossible to access should problems arise. In all horizontal waterproofing applications, choosing and correctly applying the membrane is critical, but plazas and terraces demand a more conservative approach than do roofs or parking structures. Generally speaking, the options are: Installation of a paver-on-pedestal system. Pavers are supported only at corners, with Comparison of Waterproofing Systems for Plazas and Terraces fully open joints. Membrane Puncture Crack system Installation resistance bridging Strong suit Weak spot design goals for drainage, loading, sit- ing, and usage. What are the benefits, Sheets adhered Seam quality de- Cold, drawbacks, and appropriate applica- Single-ply to deck, with Poor Fair low-odor pends on skilled glued, taped, or installation. No tions for each type of system? Here welded seams. application. redundancy. are the basics: Height restric- Multi-layer Multiple sheets Redundancy, tions may Light Duty and bonded in layers Excellent Moderate via layered preclude use in by flame or by If the plaza or terrace is designed combination cold adhesive. materials. some retrofit applications. to function as an extension of the building interior, with space for dining, Seamless, Poor adhesion or Liquid binder with smooth uneven coverage seating, or entertaining, then the finish Fluid-applied applied to deck, Good Poor transition if prepared surface will need to be nearly level, with embedded from or applied reinforcing. horizontal to incorrectly. while still allowing for the effective vertical. removal of water. For light pedestrian traffic, there are two basic options: a Choice of membrane is situation-specific, and demands holistic consideration paver-on-pedestal or sand-set system. of the entire plaza. Only by analyzing all variables, from weather to traffic Features. Paver-on-pedestal: Wa- to load limits to space constraints, can a design professional determine the terproofing membrane adheres to appropriate assembly. substrate, which slopes to drains. The substrate. The deck should be cleaned of debris and properly pre- Columnar pedestals are individually pared to facilitate adhesion. A fully adhered system prevents moisture that set, at graduated heights, atop the does penetrate the membrane from travelling underneath it. Spot repairs insulation or a protection board, to can then be completed without tearing up the entire plaza in search of the create a level support. Pavers are water entry point. then supported by a pedestal at each The protection. Drainage mats atop the membrane system direct water to corner. Open joints allow water to drains, and protection boards can provide additional coverage in high-wear- flow directly down to the sloped sur- ing areas. Insulation helps control energy costs. face below and on to drains. Sand-set: Pavers are set atop compacted sand, The paving. Structural analysis must confirm that the building can accommo- with small butt joints (approx. 1/16 of date the chosen paving system, as well as additional loading from snow, ice, an inch), into which additional sand is wind, pedestrians, and plantings. swept. Walking surface is pitched to The result. Waterproofing concerns shouldn’t undermine a plaza’s allure. bi-level drains. A well-designed, properly installed plaza or terrace creates usable outdoor Benefits. Quick and easy to install. space above a built structure, a valuable asset in a dense urban setting. Depending on material selection, light-weight systems can also be the

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least expensive. Should any problems sand composite bed, atop asphalt or Heavy Duty develop, the loose-laid pavers can cast-in-place concrete slabs separated Plazas can also be designed to with- be readily removed for maintenance, by expansion joints. Drainage takes stand heavier vehicle traffic. The two investigation, and repair. place predominantly at the surface options for durable support of cars Drawbacks. Open joints are notori- level, although bi-level drains should be and trucks are cast-in-place concrete ously problematic for high-heeled used to remove any water that does or closed-joint paving systems. penetrate below the pavers. shoes, and they can create tripping Features. Where the plaza is set on hazards should pavers become dis- Benefits. The asphalt-set paver system grade, the subgrade must be well placed. Snow removal must be done can accommodate much greater loads compacted. Insufficient compac- with a blower or shovel, as plows can without cracking or displacement than tion can result in cracking, heaving, dislodge pavers. Weight limitations can a paver-on-pedestal system, be- and premature deterioration of the may preclude not only snowplows but cause the load is supported across the paving assembly. To withstand the also, in the case of a plaza at the front entirety of each paver, rather than only rigors of vehicle traffic, hard joints, entrance to a building, emergency ve- at corners. Although the setting bed is with mortar or sealant, are preferred. hicles. It is possible to accommodate still 90% sand, the addition of asphalt A cementitious setting bed adds occasional vehicular access with an creates a more durable paving assembly durability. open-joint system, but at a significantly than the simple sand-set system. Ap- Benefits. Aggressive resistance to greater construction cost. plication of a neoprene tack coat adds traffic. Closed-joint systems can be further resilience. designed to support 40 tons or more Medium Duty Drawbacks. As the frequency and without damage. Frequent and heavy foot traffic, such weight of traffic increases, so do costs. as on a college campus or in a shop- Drawbacks. Material costs for high- Medium duty plazas are more expen- traffic plazas are greater than for ping mall, demands a more resilient sive to install than are light duty plazas, other plaza types. Maintenance, par- system. An asphalt-set system with and the level of traffic demands more ticularly of joints, can be demanding, sand-swept joints can provide a vigilant maintenance. Because asphalt- and replacement of pavers is difficult. landscaped pedestrian setting while set pavers are more secure than are Overly aggressive cleaning can blow holding up to the abuses of shoes and their light-duty counterparts, removal out joints. Mortar or sealant lifespan occasional light vehicles, like golf carts. and replacement present challenges, as should be considered as part of the Features. Modular brick, stone, or does accessing underlying waterproof- cost equation, as joint material may concrete pavers are set on an asphalt/ ing membranes. need replacement every 7-10 years. Representative Illustrations of Paving Assemblies

Finished Paving Surface Finished Paving Surface Finished Paving Surface Neoprene Tack Coat Setting Bed Setting Bed Sand Setting Bed Protection Board Filter Fabric Concrete or Insulation Processed Aggregate Asphalt Base Drainage Composit Waterproofing Sloped Concrete Fill Processed Aggregate Undisturbed Soil

Structural Deck

Subbase

Undisturbed Soil

Light-Duty on grade Medium-Duty over suspended slab Heavy-Duty on grade Drawings not to scale. Components can vary.

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THE REHABILITATION PROCESS Code Compliance Columbia University, College Walk When a plaza retrofit project is already underway is not the time to discover that building codes have changed, and that the seating for 20 must now be increased to 200, or that the plan needed to incorporate wheelchair access ramps. Local regu- lations stipulate when a plaza rehabili- tation is significant enough to demand updated code compliance. Plazas classified as “privately held public spaces” are generally subject to fairly rigid parameters governing occupancy, circulation, and hours of use, all of The existing plaza. Construction of concrete retaining walls. which will necessarily impact design. Federal, state, and municipal regula- tions incorporate evolving “green” building codes, including provisions for plaza and terrace lighting, energy conservation, and water use. Security measures may also be dictated by lo- cal law. The design team can coordi- nate lighting, signage, access pathways, and landscape elements to maximize safety while meeting ecological build- ing standards. Weight Limits Installation of granite curbs. Asphalt setting bed, ready to receive A plaza or terrace must support the hexagonal asphalt pavers. weight of pavers, landscaping elements, seating, fountains, pedestrians, and, in some cases, vehicles. Grade-level terraces may also need to bear fire equipment, in an emergency. Ret- rofitting an existing plaza or terrace requires consideration of structural load-bearing capacity, especially when a new type of system is being installed that carries significant load beyond that of the existing assembly. To avoid serious structural failure, the project architect or engineer should assess load-bearing capacity before plaza rehabilitation is undertaken.

The reconstructed pedestrian street. The redesigned paving system can withstand frequent, heavy pedestrian traffic, as well as vehicle use, while preserving the aesthetic character of the original plaza.

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Fields of Green

As green building initiatives are prompting federal, state, and local mandates on efficiency and sustainability, building codes and regulations change to reflect evolving ecological guidelines. Relevant requirements for efficient water use, storm water runoff management, light pollution reduction, and energy con- servation should be researched as part of the plaza or terrace design process. Some green ideas: • Reuse pavers, where possible, after replacing a waterproof- ing membrane, both to reduce waste and save on material expenses. Courtesy ERCO Lighting, Inc. • Use “dark sky” technology, which employs strategically positioned, low-radiance lighting, low-angle spotlights, and low- reflectance surfaces to cut down on light pollution. See sample plaza lighting diagram,above . • Choose materials that reduce the “heat island effect.” Heat-trapping materials like asphalt, tar, and non-pigmented concrete raise air temperatures in cities. Besides plantings, which dissipate heat through evapotranspiration, certain building materials, like light-colored pavers, can help moderate temperature differences. • Select native or adaptive plantings to conserve water and provide a habitat for bird and insect populations. Limit sod and turf grasses, which demand copious irrigation, mowing, and pest/weed control. • Use efficient drip systems or subsurface sprinklers, in conjunction with reclaimed water, wherever irrigation is needed. • Install “smart” controllers that vary light and water use by season, time of day, and weather. • Employ mulching, alternate mowing, and composting, low-tech solutions that protect the environment and cut upkeep costs. Above all, correct design and installation is the best way to build an environmentally sound plaza. When poor construction shortens a plaza’s lifespan, resources are wasted on rebuilding. The most ecological plaza is the one built to last.

The Final Design Drains should allow for water removal materials with their durability. not only at the surface, but at the Drainage To avoid slippery surfaces, the coef- membrane or deck level, as well. Bi- ficient of friction of various finishes Once owner’s expectations, usage, level drains prevent trapped water must be considered, as well. Ice and weight limitations, applicable building from pooling atop the membrane, snow removal approaches will also codes, and traffic exposure have been leading to premature deterioration. need to vary depending on the mate- considered and a plaza system select- A combination of trench drains, which rial selected, as some pavers respond ed, it’s time to prepare the deck slope. collect water from a larger area but better than others to deicing chemi- Some original concrete decks were are not designed for subsurface drain- cals and snowplows. constructed dead level, leading to age, and area drains, which are smaller standing water and leaks. To correct but both efficient and bilevel, is often Landscaping. Caretaking demands for the problem, slope fill may need to be the best strategy for optimal drainage. landscaping can vary widely. Some added, which can create waterproof- plantings will demand daily mowing, ing challenges during construction, as Appearance weekly pruning, or monthly replace- well as raise load-bearing concerns. Materials. Plaza design must inte- ment, as well as costly irrigation For areas that will contain tables and grate the aesthetics of the outdoor systems, while many native or adaptive chairs, a 1/4 inch per foot slope is space with those of the structure and plants can get by with only natural generally sufficient and maintains a surrounding area. Pavers of natural rainfall and minimal attention. Eco- suitable walking surface. However, stone, brick, or concrete are the most logically conscious landscaping design a 1/4 to 1/2 inch per foot slope or common options, and care must be therefore saves not only on natural more provides better drainage. taken to balance appearance of these resources, but on costs.

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Additionally, planters require spe- cial waterproofing considerations, Maintaining Your Investment including root barriers and other extra protection over the membrane You’ve invested in rehabilitating to avoid puncture. Structural load your plaza or terrace, and it looks capacity may also be an issue when great. How do you keep it up? selecting plantings; beyond the weight A little prevention goes a long way. By of the plants themselves, growing catching small problems before they media ranges in density and can add become big ones, you can extend the significant load. lifespan of your plaza and avoid the undue expense of major repairs. Water features. Fountains and pools Daily. Sweep and remove trash and debris. Check for and treat ice and demand extra attention to water- snow accumulation and clear tripping hazards. proofing, especially over occupied Weekly. Wash down plaza. Clean joints and check drains and sump pumps. space. Generally, a continuous Trim and weed plantings and check for proper operation of irrigation systems. waterproofing system is preferred, Do a safety check of railings, stairs, and lights. which can smoothly accommodate Monthly. Replace dead plantings. Repair deteriorated mortar or sealant in transitions from horizontal to vertical joints. surfaces. Size and position of water Seasonally. Inspect sprinkler systems. Perform checks of the deck for de- features may also be dictated by traffic terioration, leaks, cracks, or rust. Repair rust spots on railings, conduits, and patterns, drainage sloping, and struc- other metal. tural capacity, as well as aesthetics. Annually. Fall: Drain irrigation and sprinkler systems for winter. Spring: Con- Furniture. Seating can rest atop pav- duct a structural inspection to plan for summer repairs. ers, as with dining chairs and other Every 3-5 years. Replace sand in sand-swept butt joints. temporary furniture, or it can be If any leaks are reported, inspect and repair the waterproofing system as soon anchored to the plaza. Waterproofing as possible to avoid further damage. Know your rights within the water- and paving system options therefore proofing warranty. If the problem persists, a design professional experienced may be dependent on the quantity in plaza remediation may need to conduct a more thorough investigation. and design of any furniture or orna- mental elements. blies, such as sand-set systems, can of a plaza provides an opportunity to Lighting. Safety and appearance of a be significantly cheaper to install, but upgrade entrance and egress path- plaza or terrace at night depend on demand vigilant maintenance to keep ways to admit wheelchairs, strollers, the quality and positioning of illumina- overgrown weeds from making the or walkers, without compromising on tion. A plaza which sees significant plaza look ragged and unkempt. aesthetics. nighttime traffic will need thoughtfully For elevated plazas or terraces over designed lighting, including within foun- occupied spaces, it can be tempting to Schedule tains and around planters, to preserve cut costs by going with a less pricey All rehabilitation projects for plazas the ambiance and protect pedestri- waterproofing option, as the mem- over occupied space are, by necessity, ans. More is not necessarily better: brane lies below the surface, out of on a tight schedule, as removal of the indiscriminate use of bright lights casts view. However, scrimping on water- waterproofing system for any period stark shadows and can actually dimin- proofing can cost more than it saves of time opens the building up to water ish visibility, and it also contributes to if the membrane fails prematurely, and entry. Even plazas on grade may need light pollution. the entire paving overburden must be to remain operational during con- ripped up to replace it. struction, because of local government Budget requirements, building access issues, or Initial installation and materials costs Accessibility both. Organizing a plaza or terrace play a role in plaza design, but so do Local building codes, as well as the project into well-orchestrated phases maintenance expenses. Be sure to Americans with Disabilities Act (ADA), can permit continuous usage while ac- understand up front what upkeep will dictate the incorporation of ramps, el- complishing rehabilitation objectives. be required for any systems under evators, railings, and other accessibility The time of year at which a given consideration. Some paving assem- provisions. Substantial rehabilitation waterproofing assembly can be (continued on page 8)

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Plaza and Terrace Rehabilitation

Hoffmann Architects focuses ex- clusively on the outsides of existing buildings. A substantial portion of our practice involves diagnosing and correcting problems within plazas, ter- races, roof setbacks, and courtyards. For plazas and terraces over occupied space, Hoffmann Architects solves recurrent water infiltration by treating these areas as roofs that need extra protection, rather than as platforms for traffic on which waterproofing is merely an afterthought. We create aesthetically appealing, The George Washington University’s Eye Street Pedestrian Mall in Washington, DC. technically appropriate plaza and ter- Plaza Design and Rehabilitation race solutions by locating the sources of deterioration and developing Royal Bank of Scotland Hall targeted programs of replacement or Greenwich Capital Building repair. Project oversight and guid- Greenwich, New Haven, Connecticut ance for ongoing maintenance see the Plaza Rehabilitation Terrace, Exterior Stair, Roof, and Skylight rehabilitation through to a successful Rehabilitation and Reconstruction outcome, now and in the long term. Purchase Campus Center Among Hoffmann Architects’ plaza State University of New York (SUNY) Babbidge Library, White Building, and and terrace projects are: Purchase, New York Bousfield Hall Plaza Reconstruction University of Connecticut College Walk Storrs, Connecticut Columbia University Franklin & Marshall College Investigation and Rehabilitation of Plazas New York, New York Keiper Hall/Green Room Theatre and Exterior Stairs Plaza Reconstruction Lancaster, Pennsylvania Plaza and Stair Rehabilitation Manhattan House Phoenix Life Insurance Company O’Connor Capital Partners One American Row The Ford Foundation New York, New York Hartford, Connecticut New York, New York Roof Garden and Terrace Rehabilitation Plaza Investigation Plaza Rehabilitation State of Connecticut Office Building The World Bank The Schering-Plough Corporation 25 Sigourney Street Washington, District of Columbia Kenilworth, New Jersey Hartford, Connecticut Terrace Waterproofing System Design Plaza Investigation and Design Plaza Rehabilitation

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

ADDRESS SERVICE REQUESTED

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JOURNAL is a publication of Hoffmann Architects, Inc., specialists in the rehabilitation of building exteriors. The firm’s work includes investigative and rehabilitative architecture and engineering services for the analysis and resolution of problems within roofs, facades, glazing, and structural systems of existing buildings, plazas, terraces and parking garages.

For address changes, free subscriptions, or information on the topics discussed in this issue, contact our Marketing Coordinator at 800-239-6665, [email protected], or: This multi-level plaza over occupied space coordinates temporary and fixed furniture and planters with high- and low-traffic areas to achieve a practical, aesthetically appealing outdoor space. 2321 Whitney Avenue Hamden, CT 06518 203-239-6660 installed may also affect a rehabilitation Unfortunately, many suffer from poor project’s scheduling. For example, ad- design, inappropriate materials selec- 500 Fifth Avenue, Suite 830 hesives and fluid-applied membranes tion, faulty installation, or simply the New York, NY 10110 must generally be applied when air effects of time and the elements. If 212-789-9915 temperatures are above approxi- your plaza or terrace evidences 2611 Jefferson Davis Highway, Suite 200 mately 40°F and below 80°F, which the following or other burdensome Arlington, VA 22202 may mean scheduling installation for conditions, rehabilitation might prove 703-253-9800 late spring or early fall. Coordinating cost-effective: www.hoffarch.com seasonal restrictions with building us- • Deterioration age demands and weather events can • Decreased usage Editor: Alison Hoffmann pose significant logistical challenges. • Rising maintenance expenses Production: Cari Tate • Increased liability When to Rehabilitate: Cost-Benefit Analysis Facing an ailing plaza can be daunting. Printed on 50% recycled paper. But those who brave a plaza over- Plazas and terraces are appealing haul with forethought and care are features that attract tenants, raise rewarded with a functional, pleasant property values, and provide aestheti- open space that demands little atten- cally pleasing outdoor public spaces. tion or resources once it’s in place.