AAMA/WDMA/CSA 101/I.S.2/A440-2011, the North American Fenestration Standard known as NAFS, defines storefront as, "...a non-residential, non-load bearing assembly of commercial entrance systems and windows usually spanning between the floor and the structure above, designed for high use/abuse and strength."
The standard goes on to note, "...Storefront systems are typically designed to accommodate field fabrication and glazing and employ exterior glazing stops at one side only. Storefront employs shallow rectilinear framing profiles (approximately 150 mm [6 in] or less), which are often made available in 'stock lengths.' Vertical framing members run between the top of the floor slab and structure above, with provision for anchorage at all perimeter conditions."
Certain limitations in the use of storefront devolve from the inherent characteristics noted in NAFS. In general, for storefront systems:
- spans should be limited to 10 feet or less
- total mullion length should be less than 20 feet with no moving splices
- usage should be limited to the bottom two or three floors of the building
- glazing pockets can accept only ¼-inch monolithic glass or 1-inch insulating glass
- outside re-glazing must be acceptable
- no custom extruded profiles should be expected
- regular exterior maintenance should be anticipated
In strictest architectural parlance, a "curtainwall" is any non-load-bearing exterior wall that hangs (like a curtain) from the face of floor slabs, regardless of construction or cladding material. However, in common usage, the term curtainwall usually refers to aluminum-framed systems carrying glass, panels, louvers, or occasionally, granite or marble.
NAFS defines curtainwall as, "... a non-load bearing exterior wall cladding that is hung to the exterior of the building, usually spanning from floor to floor."
The standard goes on to note, "...Curtain wall systems can be factory-glazed or designed to accommodate field fabrication and glazing, including optional structural glazing. Curtain wall employs deep rectilinear framing profiles (approximately 150 mm [6 in] or greater), which are often made available in "stock lengths". Curtain wall vertical framing members run past the face of floor slabs, and provision for anchorage is typically made at vertical framing members only.... curtain wall systems often need to meet additional performance requirements for inter-story differential movement, seismic drift, dynamic water infiltration, etc."
Curtainwall or window wall systems should be used when performance or aesthetic expectations exceed the limitations of storefront systems. The relative merits of "stick" versus unitized curtainwall was reviewed in the December, 2009 Wausau e-newsletter "Unitized Curtainwall."
A Third Option: Window Wall
NAFS defines window wall as, "...a non-load-bearing fenestration system provided in combination assemblies and composite units, including transparent vision panels and/or opaque glass or metal panels, which span from the top of a floor slab to the underside of the next higher floor slab."
The standard goes on to note, "...Primary provision for anchorage occurs at head and sill conditions. Receptor systems can be designed as a part of drainage and movement accommodation provisions."
Wausau window wall systems can be designed to look as much, or as little, like curtainwall as is aesthetically desirable, through creative detailing of slab edge covers. Units can be installed in any sequence, and can meet the same high-performance requirements as Wausau curtainwall. Window wall systems often are provided with integral operable vents, for natural ventilation, egress, or ease of cleaning. Using Wausau's 4250i-V VisulineTM and 4250-Z Zero Sightline products, vents in the closed position are almost indistinguishable from adjacent fixed lites.
If you would like to discuss proper system selection in detail, Wausau's market managers are available as architectural support resources, and can be reached at email@example.com, firstname.lastname@example.org, or email@example.com, or visit us in Booth #313 at the AIA Expo in Washington, D.C., June 17-19, 2012. Click here for your complimentary expo floor pass.