Storefront and Curtainwall Systems Understanding the differences to deliver optimum performance, aesthetics, installation


By Tom Minnon, LEED AP, CDT


The term curtainwall usually refers to aluminum- framed systems carrying glass, panels, louvers or occasionally, granite or marble. Curtainwall selec- tion and design criteria include code compliance, structural integrity, weatherability, durability and aesthetics, plus other, application-specific needs.


Storefront framing systems are often speci-


fied for curtainwalls, but should only be used for lower structural performance applications. Storefronts are non-load-bearing glazed systems that occur on the ground floor, which typically include commercial alu- minum entrances. They are installed between a floor slab and the building structure above it. Commonly field-fabricated and field-glazed, storefronts employ exterior glazing stops at one side only. Provision for anchorage is made at perimeter conditions. Another important difference between curtainwall


and storefront, and reason for not mixing the two, is the way each handles infiltration of rainwater.


Assuming that the sill flashing is installed cor-


rectly, the most important element in controlling water penetration with storefronts is the proper fastening and sealing of end dams (5). Without end dams, water will intrude into the jamb locations of the building. To ensure water bypasses the lite of glass, deflectors must be installed wherever a horizontal mullion occurs in storefronts. Without water deflec- tors, moisture settles on the top of the glass, causing possible failure of the insulating glass unit seal.


recommended to isolate glazing pockets. A fairly recent development in these curtainwall systems is the incorporation of fiberglass pressure plates for improved thermal performance. Significant increases in condensation resistance and reductions in thermal conduction also have been recorded. To accomplish as many critical seals as possible in


controlled factory conditions and minimize dependence on field labor, “unitized” curtainwall systems have been developed. Unitized curtainwalls are factory-assem- bled and -glazed, then shipped to the job site in units that are typically one lite wide by one floor-span tall. Most unitized curtainwall systems are installed in a


The distinctions between curtainwall systems are


not absolute and are often difficult to differentiate. “Stick” curtainwall systems are shipped in


Storefronts control water infiltration by direct-


ing all internal moisture to the sill flashing (1). Most manufacturers offer sill flashing that fastens to the bottom of the opening prior to installing the storefront framing. A watertight seal is applied over the fastener heads (2) to direct water to the exterior through two weep holes at each lite of glass (3). Optional sill flash- ing also have a much higher back leg for better water performance (4).


pieces for field fabrication and/or assembly. These systems can be furnished by the manufacturer as “stock lengths” to be cut, machined, assembled and sealed in the field, or “knocked down” parts pre-ma- chined in the factory for field-assembly and -sealing only. All stick curtainwalls are field-glazed. Frame assembly requires the use of either: a) “Shear blocks” to connect vertical and horizontal framing elements, or


b) “Screw-spline” construction, in which assembly fasteners feed through holes in interlocking vertical stacking mullions into extruded races in horizontals.


Many stick curtainwalls are called “pressure


walls” because exterior extruded aluminum plates are screw-applied to compress glass between interior and exterior bedding gaskets. A snap-on cover, or “beauty cap,” is then used to conceal pressure plate fasteners. Performance of any field-assembled or field-glazed curtainwall is only as good as field work- manship allows and is limited by variables such as weather, access and job site dirt and dust. With pressure walls, many critical seals are nec-


essary, even in systems that are designed to drain or “weep” rain penetration from the system back to the exterior. Compartmentalization of each lite is strongly


sequential manner around each floor level, moving from the bottom to the top of the building. Only one unit-to- unit splice, usually a translucent silicone sheet or patch, needs to be field-sealed. Only one anchor per mullion needs to be attached to the face of the floor slab. Inter- locking unitized curtainwall frame members are weather- stripped to seal to one another, both horizontally and vertically. This accommodates thermal expansion and contraction, inter-story differential movement, concrete creep, column foreshortening and/or seismic movement. “Window wall” systems span from the top


of one floor slab to the underside of the slab above it. Window wall employs large side-stacking window units contained in head and sill receptors, also called “starters,” which accommodate movement and drain- age, but require field-applied perimeter sealants. Slab covers can be fabricated from aluminum extrusions, sheet, panels or even glass. Window walls easily ac- cept operable windows, and unlike curtainwall, can be installed non-sequentially. “Hybrid” systems combine characteristics


of multiple wall types. For example, some four-side silicone wall systems use stick wall grid frames, with factory-glazed carrier frames. The project’s final, balanced design and curtain-


wall selection should be based on all applicable crite- ria, not on any specific single number rating system. Specialty glazing contractors and manufacturers can provide design input, budget pricing, sequencing and schedule information to help building teams achieve their projects’ specific requirements.


Tom Minnon, LEED AP, CDT, is the eastern region sales manager for Tubelite Inc., Walker, Mich., serv- ing clients from Maine to Florida. To learn more, visit www.tubeliteinc.com.


www.metalarchitecture.com December 2012 METAL ARCHITECTURE 27


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52