ABSTRACT Metal and glass curtain walls proliferated after WW II, facilitated by the widespread use of air conditioning and development of sealant technology. Fixed glass required the use of suspended platforms to wash the windows and maintain the curtain wall components. The predominant systems for suspending platforms were self-propelled carriages that ran on parapet- or roof-mounted rails and concrete runways, and fixed or portable davits. Penetrations multiplied as flashing rail supports, tieback anchors, electric conduits, and code-mandated fall-arrest systems became critical. Moreover, the rooftop traffic generated by maintenance personnel threatened the watertight integrity of the roof system. This paper reviews the various window-washing systems and recommends methods to reduce damage to the roof systems. It discusses the use of pavers, walkways, and precast concrete runways. Minimizing penetrations is also discussed. The need for coordination between faqade maintenance consultants, structural engineers, and architects who design roof systems is stressed herein. SPEAKERS Mr. Justin Henshell has been a registered architect for 55 years, is licensed in NY, NJ, PA, VA, MA, FL, and Puerto Rico, and holds a certificate from the National Council of Architectural Registration Boards. He has headed his own firm since 1956. He is a Fellow of the AIA and a member of the New Jersey Society of Architects, CSI (past president Metropolitan New York Chapter), and The Masonry Society (past director). He also is a Fellow of ASTM and the recipient of the Walter C. Voss Award for 2000. He is a member of ASTM committees D 08, Roofing & Waterproofing (past chairman of Subcommittee D 08.20, Roofing Membrane Systems); C 15, Masonry Units; and E 06, Performance of Building Constructions. He serves on the International Council for Building Research Studies & Documentation, Commission W086, Building Pathology. Mr. Henshell was a faculty member and regent of RIEL Justin Henshell has authored more than 35 technical articles and papers and presented them in the U.S., Canada, and Europe on a variety of subjects relating to construction materials. He is the principal author of an ASTM standard on waterproofing design and a coau¬ thor of an NCARB monograph on Built-up Roofing. He is also the author of The Manual of Below-Grade Waterproofing Systems, published by John Wiley & Sons. In 2008, he was awarded the first William C. Correll Award by RCI for “outstanding actions beneficial to professional development of the industry.” Mr. Paul Buccellato attended Pratt Institute and is a registered architect in NY, NJ, PA, and VA and holds a certificate from the National Council of Architectural Registration Boards. He is also an RWC with RCI, Inc. He is a member of the AIA, the New Jersey Society of Architects, CSI, RCI, and ASTM, Committees D 08, Roofing & Waterproofing (chairman subcommittee D08.20, Roofing Membrane Systems; past vice chairman of Subcommittee D 08.22, Waterproofing); and C 15, Masonry Units; and recipient of the Award of Merit and a Fellow of ASTM International. He is a mem¬ ber of the Masonry Contractors of New Jersey. He has authored several technical papers on waterproofing and roofing, five ASTM standards on roofing and water¬ proofing, and has lectured at Brookdale College in New Jersey, and presented papers to various organizations. He wrote a column on roof design for The Roofing Specifier and is a coauthor of an NCARB monograph on built-up roofing. Mr. Buccellato is the mayor of Matawan, NJ. CONTACT INFO: 732-530-4734 E-mail: n.henshell@verizon.net paul . buccellato@verizon . net Henshell & Buccellato – 82 Proceedings of the RCI 24th International Convention
ABSTRACT Metal and glass curtain walls proliferated after WW II, facilitat¬ ed by the widespread use of air conditioning and development of sealant technology. Fixed glass required the use of suspended platforms to wash the windows and maintain the curtain wall components. The predominant systems for suspending platforms were selfpropelled carriages that ran on parapet- or roof-mounted rails and concrete runways, and fixed or portable davits. Penetrations multiplied, as rail supports, tieback anchors, electric con¬ duits, and code-mandated fall¬ arrest systems became critical. All of these penetrations required roof system openings and flash¬ ings that weaken the waterproof¬ ing system. Moreover, the rooftop traffic generated by maintenance personnel threatened the water¬ tight integrity of the roof system. This paper reviews the various window-washing systems and rec¬ ommends methods to create and maintain the watertight integrity of the roof systems. It discusses the use of pavers, walkways, and precast concrete runways and how to minimize penetrations. The need for coordi¬ nation between facade mainte¬ nance consultants, structural engineers, and architects who are involved in the design of roof sys¬ tems is emphasized. INTRODUCTION Prior to the advent of the metal and glass curtain wall, medium- and high-rise buildings were constructed with punched windows separated with masonry¬ clad columns and spandrels. Windows were operable because air conditioning was not in wide¬ spread use, and operable sash was required for ventilation. These windows were washed by men equipped with safety belts, which were secured to win¬ dow-cleaner anchor bolts. Their design was controlled by FM, UL, and local codes. Window washers worked from boatswains’ chairs, swing stages, or scaffolds secured by C-hooks, over parapets or from cables con¬ nected to rings through the mem¬ brane secured to the roof deck framing. With the widespread introduc¬ tion of air conditioning, operable windows were no longer required for ventilation. As air-conditioned buildings proliferated, metal and glass curtain walls with fixed glaz¬ ing became more feasible. Fifty years ago, Lever House (Figure 1), the New York City “glass box,” ushered in the era of high-rise buildings clad with metal and glass curtain walls. Soon, similar buildings became a part of the landscape in every major city. Accelerated by the rapid improvement of HVAC sys¬ tems, these buildings had few, if any, operable sashes, which pre¬ sented a problem for cleaning the glass and maintaining caulking. Figure 1 Today, most of the metal and glass curtain walls on high-rise buildings are maintained from scaffolds or platforms suspended from window-washer carriages that circumnavigate the perimeter of the roof, traveling on concrete runways or rails. Buildings with many setbacks are equipped with permanently mounted davits or davit sockets to receive portable davits. For nonwindow-washing maintenance, if required, portable outrigger beams are often speci¬ fied. Currently, OSHA/ANSI stan¬ dards require compliant fall pro¬ tection and suspended mainte¬ nance equipment on all buildings. Two anchors are required: one for a tieback, and the other for a fall arrest line. This poses a challenge to roof designers who must design systems that will resist the poten¬ tial for water infiltration at these numerous penetrations and from abuse by maintenance personnel. One of the most common building maintenance systems is an electric-powered, self-propelled Proceedings of theRCI 24th International Convention Henshell & Buccellato – 83 carriage with a scaffold suspend¬ ed from its davits. The scaffold may be swinging or equipped with fittings to engage guides that are integral to the vertical curtain wall mullions. By raising or lower¬ ing the scaffold and moving the carriage, the entire fapade is accessible for cleaning and main¬ tenance. The carriage travels on a concrete runway or is mounted on tracks that may be secured to the parapet or supported on pedestals. It is commonly housed on the roof in “garages” for protec¬ tion and maintenance. WINDOW-WASHING SYSTEMS PORTABLE ROOF OUTRIGGER BEAMS Description This is one of the least sophis¬ ticated maintenance systems. It consists of two portable, extend¬ able outrigger beams with a fitting on one end to secure to the tieback anchor and a pair of wheels mounted on a tripod and located near the eave or parapet (Figure 2). The beams are carried or sometimes dragged across the roof, positioned, and secured at the inboard end to the anchor fit¬ ting. Problems Portable Roof Outrigger Beam systems present the following concerns: • The wheels on the tripod can cut into the roof membrane or force aggregate into it. • Smooth-surfaced and single¬ ply membranes are subject to abrasion. • Loose-laid membranes will wrinkle from the wheel shear. • Insulation below the mem¬ brane may have insufficient Figure 2 compressive strength to resist the point loads of the tripod wheels. Recommendations A good design for this type of system should incorporate a row of precast 600-mm x 600-mm (24- in x 24-in) pavers near the eave or parapet that will provide perma¬ nent support for the wheels of the tripod. Typically, plywood sheets are utilized to provide protection and to isolate the wheels and equipment from the membrane. However, plywood can deteriorate over time and cause damage to the roof membrane. Careful coor¬ dination is required with the facade maintenance engineer to properly locate the anchors and the pavers. Pavers should be stur¬ dy and set solidly on the mem¬ brane to resist cracking from the wheel loads. DAVITS Description Davits consist of a telescoping outrigger beam mounted on masts. They are bolted to a socket on a pedestal secured to the roof structural framing system. Hoists and platforms are suspended Figure 3 from the outrigger (Figure 3). Davits can be permanently mounted on the roof or are portable and are fitted into per¬ manent sockets connected to the roof structural system. Op¬ tionally, masts can be tied back to a roof-mounted anchor, but usu¬ ally the structural support is suf¬ ficient to resist the moment forces from the hoist and platform. Henshell & Buccellato – 84 Proceedings of the RCI 2 4 th International Convention Problems The davit supports consists of a flat plate welded to a post. The height of the davit is often determined from the top of the struc¬ tural deck by either the facade mainte¬ nance engineer or structural engineer without determining the level of the height above the membrane. Since the membrane level varies when tapered insulation is used, the level of the membrane at each da¬ vit may not be deter¬ mined at the time the post height is selected. Energy Code require¬ ments or Mechanical Electrical Plumbing Figure 4 Engineer (MEP) crite¬ ria and future reroofing may result in the top of the post flash¬ ing being too low to conform to industry standards or the mem¬ brane manufacturer’s require¬ ments. Recommendations Coordination among the architect, engineer, and facade maintenance consultants at the beginning of the project can elim¬ inate flashing problems from inadequate pipe heights. Prudent roof designers will provide pavers where davits are to be located to reduce abuse from maintenance personnel. Walkway pads can be used, but protection Figure 5 of the membrane is reduced. CARRIAGES ON RAILS Description Carriages or trolleys are usu¬ ally self-powered and can be mounted on a monorail secured to the inboard face of the parapet or to pairs of rails mounted on sup¬ ports above the roof. Roof-mount¬ ed rails are usually installed close to the surface of the roof and may incorporate complicated switching gear. They also require local power supplies mounted on the roof and spaced to minimize the length of the cables (Figures 4 and 5). Problems Parapet-mounted rails rarely pose problems. However, it is desirable to provide pavers for the operators to walk on for accessing the equipment. Roof-mounted systems with their switching gear can inhibit Proceedings of the RCI 2 4th International Convention Henshell & Buccellato – 85 roof maintenance and pose difficult flashing and reroofing condi¬ tions. Recommendations If the building de¬ sign requires or incor¬ porates the use of a carriage or trolley win¬ dow-washing system, it is best to use a parapet- mounted rail sys¬ tem in lieu of a roof¬ mounted rail system for the reasons de¬ scribed above. It is bet¬ ter, although not ideal, to utilize the system to operate over a concrete runway. CARRIAGES ON CON¬ CRETE RUNWAYS Figure 6 Description Self-propelled carriages travel¬ ing on concrete runways are more predominant than track-mounted units for buildings with minimum setbacks. Runways are construct¬ ed of a reinforced-concrete slab, approximately 3 m (10 ft) wide that follows the parapet around the building perimeter (Figure 6). The outboard side terminates within a few centimeters (inches) of the inboard face of the parapet. The inboard side of the runway is provided with a 100- to 150-mm- (4- to 6-in-) high curb to prevent the carriage from straying off the runway (Figure 7}. Rings or pre¬ fabricated, flush-mounted tie¬ downs are installed on or near the curb to help counterbalance the scaffold. The curb is equipped with scup¬ pers or drains at regu¬ lar intervals. Until a few decades ago, the membrane below the runway was constructed as a multi¬ ply bitumen-and-felt built-up roof (BUR) installed over insula¬ tion (or directly on the concrete deck, if insu¬ lation was not re¬ quired). A variation of this system is a PMR configuration in which the membrane is in¬ stalled on the roof deck, covered with loose-laid, extruded Figure 7 polystyrene insulation, Henshell & Buccellato – 86 Proceedings of the RCI 24th International Convention case). From a roof maintenance and replacement standpoint, it was another stoiy. Most high-rise buildings are designed to last from 50 to 75 years, and some for as long as a century. On the other hand, it is generally agreed that roofs are considered to perform successful¬ ly if they can be maintained leakfree for 20 years. Thus, an aver¬ age roof on an average high-rise building will require replacement at least once and, more than like¬ ly, twice before the building has outlived its useful life. When this occurs, the concrete runway becomes a white elephant; it is too big and too expensive to remove and ballasted with aggregate or pavers. Contemporary mem¬ branes run the gamut of liquidapplied membranes; BURs with polymer -modified bitumen plies, ;and loose-laid thermoplas¬ tic and thermoset, single-ply sheets. In the absence of a PMR system, window-washer runway slabs were cast over cap sheets or preformed asphalt/ felt protection boards laid dry or mopped to the membrane. OSHA/ANSI- and ASMEapproved, self-propelled, wheeled carriages or trolleys support out¬ riggers with their hoists and plat¬ forms. They run on cast-in-place concrete runways divided with control joints. Problems Most slabs are cast in 3-m (10-ft) lengths with 25-mm (1-in) joints. These joints are filled with a preformed expansion joint filler and caulked. The caulking may extrude in the summer where it is often damaged by the carriage’s wheels. The joints are intended to absorb thermally induced move¬ ment, and are thus dynamic. Since the slab is floating, its movement can impart shear stresses to the membrane and when the slab is cast around tie¬ down anchors that are secured to the deck structure through the roofing system and therefore limit the slab’s movement. Runways also deteriorate from freeze/ thaw cycles as well as from the wheels in cases where the turning radius of the carriages or trolleys is short (Figure 8). Cast-in-place concrete paving proved to be a satisfactory wear¬ ing surface for window-washer carriages, providing it was proper¬ ly reinforced and of good quality concrete (which is not always the and incapable of being made watertight for a reasonable time when the roof below it leaks. If roof replacement is not required, roof maintenance cre¬ ates another problem. The slab inhibits access to the parapet base flashing for repairs because it is cast against or in close prox¬ imity to the parapet base flashing. And repairs are required more fre¬ quently because the slab move¬ ment often damages metal flash¬ ing end joints or abrades compo¬ sition flashing as discussed above. abrade or tear the base flashing. More serious problems develop Figure 9 Proceedings of the RCI 24th International Convention Henshell & Buccellato – 87 Figure 10 Figure 11 conto tural deck, form TIE-BACKS AND HOLD-DOWNS run over crete runway is the most common substrate for a window-washing carriage to circumnavigate the perimeter of the roof, its durabili¬ ty is shortened by the need to remove it in part or whole to repair or replace the roof or water¬ proofing membrane below. The effects of freeze/thaw cycles will also cause the runway to deterio¬ rate. pedestal, although some are Ushaped and countersunk flush with the roof or with the concrete runway (Figures 12 and 13). Reinforced precast concrete panels provide a structurally sound substrate for the window¬ washing unit to travel and trans¬ verse the roof perimeter. The panelized runways provide the follow¬ ing advantages: for re¬ Description Window-washing sys¬ tems require tie-backs for personal fall protection systems. Tie-backs and hold-downs are also re¬ quired to counteract the overturning forces of car¬ riages that support outrig¬ gers, boatswains’ chairs, and davits. These are usu¬ ally anchored to the strucframing supporting the Anchors are usually in the of a ring mounted on a Recommendations Although a cast-in-place Problems Tie-backs and hold-downs are usually specified by the faqade maintenance consultant and indi¬ cated on both his drawings and the drawings produced by the structural engineer. These are items manufactured to conform to codes and are not often indicated on the architect’s roof plan. As discussed under davits, the pedestal heights are frequently specified by the engineer or facade maintenance consultant who may not be aware that tapered insula¬ tion systems can create varying reinstalled as required roof maintenance and placement They can be designed incorporate tie-down anchors that do not penetrate the roof/waterproofing system • If and when panels are dam¬ aged or deteriorate, individ¬ ual units can be easily re¬ placed Based on experience from pre¬ vious attempts to repair mem¬ branes and flashings under cast¬ in-place runways, constructing the same runway from precast units can improve the durability of roofing systems (Figures 10 and 11). They create runways that are independent of the roofing/ waterproofing and flash¬ ing systems They can be removed and way can be “water¬ proofed,” the expan¬ sion joints, the joint between the runway and the parapet flashing, and the joint between the runway curb and roofing remain dy¬ namic and well be¬ yond the elastic ca¬ pabilities of liquid coatings. Elastomer¬ ic sheet materials are equally ineffec¬ tive because they are vulnerable to dam¬ age from the car¬ riage’s wheels when they against the parapet or twist the expansion joints. In an effort to avoid the finan¬ cial and logistical headaches of removing some or all of the run¬ way to effectuate repairs, attempts have been made to seal the runway and thus stop water infiltration into the concealed penetrations (i.e., tiebacks, an¬ chorage, etc.) and flashing below it. This is rarely successful. Where a coating was applied to the run¬ way surfaces, we observed prema¬ ture failure of the coating (Figure 9). Although the field of the run- Henshell & Buccellato – 88 Proceedings of the RCI 24th International Convention heights above the structural deck. Consequently, the industry stan¬ dard for flashing membrane pene¬ trations is often violated. Tie-backs on standing seam roofs create another problem with coordination between the facade maintenance consultant and the architect who lays out the spacing of the standing seams. Again, the detailed by the structural engi¬ neer or facade maintenance engi¬ neer without input from the archi¬ tect who selects the insulation and slopes. Recommendations Flush or countersunk tiebacks or hold-downs should be avoided. Their use creates flashprovide heights above the roof membrane that will eliminate flashing problems and avoid vio¬ lating industry standards. Consideration should also be given to future reroofing and the potential requirements for even greater thermal resistance. Figure 13 Figure 12 reing issues, whether installed in the roof area or a concrete run¬ way. Since tie-backs or Note that tie-backs in the plane of the roof are located and their height determined and Recessed U-bolts and rings also create problems where the enclosure is below the mem¬ brane or runway surface. Tie¬ downs that are cast into the run¬ way are particularly difficult to flash to the membrane and almost impossible to waterproof at the slab surface. As with davits, tiebacks and hold-downs should be designed to hold-downs are tie-back locations are not always indicated on the architectural drawing. This can result in inter¬ rupting the standing seam (Figure 14) and creating stress concentrations . CONCLUSIONS Each type of facade and win¬ dow washing maintenance system can generate its own unique prob¬ lems. However, the one common problem that they all share is the potential for abuse and subse¬ quent premature failure of the roof system. Understanding the common design requirements and the ancillary elements of the window¬ washing system can reduce or eliminate these problems. Coordinating the design of the window-washing system with the roof design from the beginning of the project can save countless hours in redesigning the flashing quired by code or OSHA for personal fall protection or to coun¬ ter the overturning forces of the carriage, it is important that their design, heights, and locations be coor¬ dinated with the archi¬ tect, engineer, and faqade maintenance consultants. Proceedings of the RCI 24th International Convention Henshell & Buccellato – 89 systems or correcting problems after the project is completed. Platforms for these systems are electrically powered. Outlets that are mounted on concrete runways have conduits that pene¬ trate the waterproofing membrane located under the runway. Movement of the runway, by either thermal or braking loads, can cause failure of the flashing at the conduit. Additionally, during placement of the concrete, the flashings can be damaged. It is better to locate and mount the outlets on the interior face of the parapets. Conduits should be located to avoid penetrating the roof or waterproofing membrane. Rooftop traffic to operate and maintain the window-washer sys¬ tem often results in abuse of the roof membrane. Providing walk¬ ways to the equipment and a suit¬ able protection layer under the equipment will help reduce or eliminate damage to the roof membrane. Consideration should be given to using pavers or walk¬ way pads beyond the equipment area to afford better protection of the roof, including locating them around tie-backs or anchorage units. If the window-washing system is designed to travel on a concrete runway, the engineer should con¬ sider designing the tie-backs into the runway curbs. This would Figure 14 eliminate a penetration through the roof or runway and the subse¬ quent difficulty of flashing the tieback or anchorage unit. If the window-washing system design requires a concrete run¬ way, consider using precast seg¬ mented concrete units. The units create runways independent of the roofing and flashing and can be removed and replaced for maintenance. KEYWORDS Window-washing systems, davits, tie-backs, runways, car¬ riages, high-rise buildings, glass curtain walls REFERENCES Justin Henshell and Paul Buccellato, “Precast Concrete Pavers for Parking Decks: Building Deck Water¬ proofing,” ASTM STP 1084, 1989. Justin Henshell and Paul Buccellato, “Extending the Dura¬ bility of Concrete Window- Washer Runways,” Proceed¬ ings of the 8th International Conference on Durability of Building Materials & Com¬ ponents, Vancouver, Canada, May-June 1999. Henshell & Buccellato – 90 Proceedings of the RCI 24th International Convention
