The curtain wall should be designed for accessibility for maintenance. Revised by the Chairs of the Building Enclosure Councils with assistance from Richard Keleher, AIA, CSI, LEED AP and Rob Kistler, The Facade Group, LLC Each glazing pocket should be fully isolated from adjacent glazing pockets. The glass unit is slid into a deep glazing pocket on one jamb far enough to allow clearing the opposite jamb and is then slid back into the opposite glazing pocket and then dropped into the sill glazing pocket. This elevation shows a typical stick-built curtain wall set in a punched opening in a masonry cavity wall. Appropriate use and application of the concepts illustrated in these details will vary based on performance considerations and environmental conditions unique to each project and, therefore, do not represent the final opinion or recommendation of the author of each section or the committee members responsible for the development of the WBDG. Aluminum framed wall systems date back to the 1930's, and developed rapidly after World War II when the supply of aluminum became available for non-military use. Unlike discontinuous windows, which are smaller units and can rely to a high degree on sill flashings to capture frame corner leakage, curtain walls cover large expanses of wall without sill flashings at each glazed opening. Some designs provide one upstanding leg that provides one line of defense against air and water infiltration. Some "poured and debridged" polyurethane thermal breaks shrink and stress forms in the thermal break when the exterior aluminum moves differently from the interior aluminum due to temperature differences. More information about AAMA and its activities can be found on the AAMA website. The CRF does not give information about cold spots that could result in local condensation. Steel can be added to a unitized system to increase its spanning capability. Also, the use of low-e and spectrally selective glass coatings can significantly reduce energy loads and improve comfort close to the wall. Unusual or custom details, such as copings, deep sills, projected windows, spandrel areas and shadow box can dramatically alter performance. Curtain wall systems range from manufacturer's standard catalog systems to specialized custom walls. Units are hung from the top or face of the adjacent floor or building structure using mated brackets and field applied bolts with a minimum of clearance for access and assembly. Lateral load resistance requirements (wind loads, spans) generally dictate frame depth. The frame is fixed and exterior dry gaskets are installed. Back pans are metal sheets, usually aluminum or galvanized steel, that are attached and sealed to the curtain wall framing around the perimeter behind opaque areas of a curtain wall. Details are not provided for interior glazed systems because air infiltration is a concern with interior glazed systems. However, unlike a stick system which has an integral hollow shape, the split mullions must be allowed to move independently to accommodate the building movement thus complicating the introduction of steel. Glazing problems specific to curtain wall construction include visual obstruction from condensation or dirt, damage to opacifier films from material degradation, condensation and/or heat build-up, and IGU issues/laminated glass issues. Also placing the stack joint above the floor provides a more convenient location for field workers to achieve the critical seal at the four-way intersection. Vision glass is predominantly insulating glass and may have one or both lites laminated (see Glazing), usually fixed but sometimes glazed into operable window frames that are incorporated into the curtain wall framing. Wind load bracing should be incorporated at the single span height to avoid increasing the vertical mullion dimension to accommodate the increased span. "Smart" Curtain Walls, like smart windows, control visible light transmittance by employing electrochromic or photochromic glass coatings; see the discussion in Glazing. Careful detailing can provide a method to thermally isolate the cavity from the interior. Buildings in cold climates have struggled throughout the ages with ice and snow formations that slide, fall, or get windblown from their roofs, ledges, and window sills, causing harm to people and damage to property below. Design the drainage system to handle condensation as well as rain. Curtain Wall. A substantial ½" thick minimum poured smoke-seal is required to separate air return and supply plenums from each other, and for infection control in hospitals. Davits and fall arrest safety tieback anchors should be provided on the roof and stabilization tie-offs provided on the face of the wall to comply with OSHA standards CFR 1910.66, CFR 1910.28 and ANSI/IWCA I-14.1 "Window Cleaning Safety Standard". Integrate curtain wall sill flashings with sill flashings or base of wall flashings of adjacent walls. Projects for which condensation control is a critical concern, such as high interior humidity buildings, require project-specific finite element analysis thermal modeling using software such as THERM. Aluminum frames are inherently corrosion resistant in many environments if anodized and properly sealed or painted with baked-on fluoropolymer paint. Select a curtain wall with a demonstrated track record in similar applications and exposures. Glazing pocket weeps are protected from wind-driven rain and pressure by a glazing trim cover containing weep slots in the bottom which are offset from the sill glazing pocket weep slots and the glazing setting blocks at glazing panel quarter points. The details associated with this section of the BEDG on the WBDG were developed by committee and are intended solely as a means to illustrate general design and construction concepts only. This can be accomplished by increasing the thickness of one of the lites of glass or by incorporating a laminated layer of glass with a noise-reducing interlayer, typically a polyvinyl butyral or PVB. The acoustic performance of curtain walls is primarily a function of the glazing and internal seals to stop air leakage (covered elsewhere). Disclaimer, Unified Facilities Guide Specifications (UFGS), American Architectural Manufacturers Association, Considerations for Building Design in Cold Climates, Unified Facility Guide Specifications (UFGS), Federal Guide for Green Construction Specifications, American Architectural Manufacturers Association (AAMA). Unit dimension of mating head and sill extruded profiles allows for specified floor to floor deflection at the stack joint. Face-sealed, water-managed and pressure-equalized rainscreen systems are the three systems that are available. Laboratory testing: For projects with a significant amount of custom curtain wall, require laboratory testing of a mock-up curtain wall prior to finalizing project shop drawings. Products, Proper placement of insulation at the curtain wall perimeter reduces energy loss and potential condensation issues. Careful integration with adjacent elements such as other wall claddings, roofs, and base of wall details is required for a successful installation. The movement of the glass within the frame and the movement forced in the anchors tend to induce additional stresses into a stick framed system. This system provides reasonable performance but is susceptible to leaks at corners or joints in dry gaskets. It is recommended that consultants be hired with an expertise in custom curtain wall design for projects that incorporate these systems.  AAMA (American Architectural Manufacturers Association), 1996, ‘Curtain Wall Design Guide Manual’  Dudley McFarquhar, Ph.D., P.E- The Role Of The Building Façade- Curtain walls  Www. The splice between the vertical mullions will also be designed to allow vertical movement while providing lateral resistance. Single or double glazing can be used at the spandrel area which is backed by a finish metal panel to form a shadow box. Isometric of Open Stack Joint Unitized Curtain Wall System (Figure U–2) PDF, Isometric of Completed Stack Joint Unitized Curtain Wall System (Figure U–3) PDF, Vision Glass Jamb Unitized Curtain Wall (Figure U–4) PDF, Unit Stack Joint Unitized Curtain Wall (Figure U–5) PDF, Intermediate Horizontal Unitized Curtain Wall (Figure U–6) PDF, Jamb at Spandrel Area with Anchorage to Slab Unitized Curtain Wall (Figure U–7) PDF, Unit Anchor to Slab Edge Section Unitized Curtain Wall (Figure U–8) PDF. AAMA and IGMA, two industry leaders, have unified to form an exponentially stronger alliance. Perimeter sealants, properly designed and installed, have a typical service life of 10 to 15 years although breaches are likely from day one. Development and review supported through a grant from the American Architectural Manufacturers Association. More robust systems will also include a gasket at the interior interlock. Shadow box construction creates the appearance of depth behind a transparent lite of glass by incorporating a metal sheet into the curtain wall behind the lite.