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.
"Stick" curtainwall systems are shipped in pieces for field-fabrication and/or -assembly. These can be furnished by the manufacturer as "stock lengths" to be cut, machined, assembled, and sealed in the field, or as "knocked down" (KD) parts pre-machined 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.
Performance of any field-assembled or field-glazed curtainwall is only as good as field workmanship allows, limited by variables such as weather, access, and job site dirt and dust. Many critical seals are necessary, even in systems that are designed to drain or "weep" rain penetration from the system back to the exterior.
To accomplish as many of these critical seals as possible in controlled factory conditions, and minimize dependence on scarce and expensive field labor, "unitized" curtainwall systems have been developed.
Unitized curtainwalls are factory-assembled and -glazed, then shipped to the job site in units that are typically one lite wide by one floor tall. Only one unit-to-unit splice (usually a silicone sheet or patch) needs to be field-sealed, and only one anchor per mullion needs to be attached to the face or top of the floor slab. Interlocking unitized curtainwall frame members are weatheripped 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. Most unitized curtainwall systems are installed in a sequential manner around each floor level, moving from the bottom to the top of the building.
CHOOSING BETWEEN STICK and UNITIZED CURTAINWALL SYSTEMS |
Selection Criteria |
Stick Curtainwall |
Unitized Curtainwall |
Project Size |
Small |
Large |
Wall Configuration |
Complex
(Many changes in plane, e.g. soffits, corners, etc.) |
Repetitive
(Large expanses of flat wall) |
Joint Pattern |
Random |
Uniform horizontal sill line |
Glazing |
Field |
Factory |
Inter-story Movements |
Very limited |
Inter-locking frames accommodate movements |
Quality Control |
Subject to site variables
(Both environment and equipment) |
Controlled factory conditions |
Modification |
Can be cut-to-fit in the field |
Pre-engineered |
Sealing |
Subject to site variables |
Minimal field sealing |
Field Labor Cost |
High
(Many parts to track and assemble) |
Low |
Field Labor Duration |
Slow |
Fast
(Often setting 75 sqft or more per unit) |
Access and Safety |
Exterior access required |
Set from the interior
(Exterior optional) |
For buildings using curtainwall systems as design elements, it is important to consult with an experienced manufacturer early in the process. Teamed with a reputable, local glazing subcontractor, manufacturers can provide design input, budget pricing, sequencing, and schedule information that will prove invaluable to the design team. Wausau market managers are available as architectural support resources, and can be reached at education@wausauwindow.com, healthcare@wausauwindow.com, or government@wausauwindow.com. |