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Steel Curtain Wall FAQ - Architectural Glass and Framing Questions
Most Popular Questions Asked
Q
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What is the cost differential between steel curtain wall systems and a reinforced aluminum system?
A
Generally speaking, given their higher performance, steel curtain wall systems have a price premium compared to standard aluminum assemblies. However, there are several material and installation factors that can help offset the greater initial cost. From a material standpoint, steel systems do not require cladding or the associated fabrication and material shipping costs. Because steel systems have fewer materials to install, installation time and labor costs can be reduced. As a comparison, in a reinforced aluminum curtain wall installation, contractors set the vertical structural steel tubes and the horizontals steel assemblies, then clad the assemblies. With SteelBuilt Curtainwall® Systems from Technical Glass Products (TGP), the structural elements are also the finished materials, so installation is more straightforward and less labor intensive.
Q
What finishes are available for steel curtain wall systems? Are there any special coatings required to prevent corrosion?
A
SteelBuilt Curtainwall® Systems can be either powder- or wet-coated to match any desired color scheme, using any coating suitable for Architecturally Exposed Structural Steel (AESS). The exterior caps or interior back mullions can be made from stainless steel to match other building elements. With stainless steel, brushed and bead-blast finishes are the most common, while exotic stainless finishes such as angel hair, swirl patterns, etc. can be incorporated at a higher price.
TGP provides steel framing with high anti-corrosion protection, such as double-sided pre-galvanization, which is then top-coated with a durable primer and finish color. Gaskets help isolate water from contacting the steel components. No special coatings beyond these are required to prevent corrosion.
While field painting is an option, TGP recommends against it as factory painting helps protect the steel during transportation and installation on the jobsite.
Q
Are there any issues with dissimilar metals where aluminum cover caps connect with steel backing?
A
Typically there is no direct contact between steel and aluminum components so galvanic action is not an issue. In SteelBuilt Curtainwall® Systems, the aluminum pressure plates are connected to the steel back members only through the stainless steel pressure plate screws. Because these metals (stainless steel and aluminum, and stainless steel and carbon steel) are close proximity to each other in anodic polarity, they tend not to corrode in saltwater environments as fast as metals that are further apart on the electromotive scale. Also, if one of the metals is coated with a non-conductive paint or finish, this effectively isolates the two materials.
Q
What is the typical maximum height allowed for a steel curtain wall installation?
A
The maximum height allowed depends on many aspects of the building design, but multi-story applications can readily be used. The primary factor influencing maximum height is where the dead load weight of the wall will bear on the structure. If the entire dead load can be applied to one floor, then no open-splice joints are required. If the wall is supported by multiple floors, then the live load deflection of individual floors has to be accommodated, and open splice joints will be needed in the curtain wall members (whether they are steel or aluminum). This affects the face dimensions of the system ultimately detailed. For example, the horizontal above the mullion splices will typically be at least 3-4” wide to accommodate anything more than 3/8” live load deflection. Another factor impacting the curtain wall height is thermal expansion and contraction. While steel has a lower thermal expansion coefficient than aluminum, over large distances this movement must be accommodated. The building structural engineer and frame supplier can work with the architect to address structural performance in concert with the aesthetic intent of the design.
Q
What elements are required for the system to earn a fire rating?
A
To receive a UL fire rating, the curtain wall system components are required to be tested as an assembly. This includes the glass, exterior caps, back framing members, seals, fire-safing, etc. of the particular system configuration. The design options are more limited for fire-rated curtain walls; the shapes and details shown in most manufacturers’ literature is the limit of selection available. Custom systems typically require additional testing. It is also important to note that fire-rated curtain wall must be anchored into surrounding fire-rated construction and that there are code limits on the sizes of individual glass lites. An intumescent coating is not required for fire-rated applications. Because fire-rated curtain walls have additional code requirements compared to non-rated applications, it is important to discuss your project needs early with TGP to determine what solutions are possible.
Q
What is the availability of large lites of glass and what is the glass fabricator's ability to achieve high performance coatings on these large sizes?
A
For SteelBuilt Curtainwall® Systems, TGP is the framing supplier and the glazing must be sourced from a glass manufacturer (this differs only for fire-rated installations, where TGP supplies both glass and framing for a fire-rated system). The specific glass lite sizes will thus depend on the capabilities of those manufacturers. As a general indication, Viracon and Oldcastle, two of the larger, more recognized glass fabricators, publish 84” x 144” as the largest sizes they will produce for any of their standard fabrication, including Low-E coatings, constructing insulating glass units, laminating, etc. Other manufacturers, such as Rochester Glass, will produce larger lites, which typically must be thicker. Contact a glazing manufacturer in your area for details on what glass lite size options are available. The SteelBuilt products can support any glass lite that can be fabricated. The individual frame components are sized to carry those imposed wind and dead loads, typical to any framing material.
Q
What elements are included in the system to protect against moisture intrusion?
A
The system includes a continuous gasket across the full width of the frames, which prevents water from coming into direct contact with the steel back members. To further prevent water intrusion, the installer must seal the lapped joints at the horizontal-to-vertical gasket joints.
SteelBuilt Curtainwall® Systems are generally weeped through the sill of the verticals only. There are no zone dams in these steel systems, as is typical with aluminum pressure plate systems. This eliminates the need for the steel system to be weeped at every horizontal member.
Condensation resistance in steel systems is better than aluminum assemblies since there is no metal in the glazing pocket, as compared to aluminum systems that typically have tongues in the unheated space that can conduct heat through the wall. Heat transfer through steel is also lower than through aluminum. For an additional barrier to heat transfer, the steel system does not have metal in the cold space of the glazing pocket that is kept completely behind the air and water gasket barrier. Depending on the glass, the Condensation Resistance Factor (CRF) for steel curtain wall ranges from 40 (45 mm wide system, stainless caps, 1” IGU / clear glass) up to 63 (triple glazed Solarban 60, argon gas-filled air spaces).
Q
How is water controlled in the glazing pocket for steel curtain wall systems?
A
In aluminum systems, each individual lite is zoned off from other glazing and water is weeped to the exterior through the horizontal pressure plates at the base of each lite. In TGP's SteelBuilt Curtainwall® Systems, isolating each lite is not required, therefore horizontal pressure plates do not have weep holes placed in them. Through the gasketing, water is kept off the tops of insulating glass units and directed to the verticals. Water then is directed to the exterior at the base of the verticals. This is one of the factors that allows water penetration resistance per ASTM E331 to reach 15 psf as a minimum.
Q
Are interior welds visible in a steel curtain wall system?
A
The system's horizontal-to-vertical connections are not welded, but are typically joined with hidden shear blocks and concealed fasteners in most applications, including fire-rated curtain walls. For the profiles themselves, the rolled “standard” curtain wall profiles there are no visible welds. On the laser-welded profiles that can be used as back members with a SteelBuilt Curtainwall Infinity™ System, the welds are only visible on the inside corner of I-beams or T-profiles. Such beads are less than 1/32” in diameter and are continuous and smooth with no gaps, they are typically only visible at a very close distance. On corners of tubes or certain other shapes where a weld might be seen, if it is accessible, TGP will grind the weld smooth so it is not visible after the profile is finished.
Q
What is a typical wall effective U-value for a steel glazed curtain wall?
A
The glass, more than the framing, is the primary driver of the overall assembly’s U-value. NFRC testing is based on a standard window size. Due to the fact that a project’s curtain wall glass sizes are larger in the real world application, the ratio of glass to framing is much higher, and U-values are lower than the tested specimens.
TGP’s rolled profiles, under NFRC testing, have been measured as high as 0.51 btu\hr*F*ft2 with 1” IGU comprised of clear glass and non-gassed airspace, and as low as 0.19 btu\hr*F*ft2 with triple glazing, Solarban 60 clear with argon filled airspaces. The laser-welded profiles, under Therm modeling, have been calculated at 0.36 btu\hr*F*ft2 using clear glass with Viracon VE1-2M coating on #2 surface with a fully captured system. Using a laser welded profile and rolled horizontals, only structurally glazed (and not captured), resulted in a U-value of 0.39 BTU /hr*ft2*˚F.
Q
How does expansion and contraction affect curtain walls with steel and aluminum components?
A
The steel in the SteelBuilt system is located completely on the building interior once the wall is enclosed, thus it is not exposed to the temperature range of 180° F that most specifications require for design / performance value. Although the aluminum pressure plate is on the exterior, it typically is not in direct sun given the system configuration. As a result, while some heat transfer may take place between the pressure plate and the exterior cap, the differential movement between the materials is not substantial enough to adversely impact the wall performance.
For instances in which the cap and pressure plate are made of different metals, there typically will be some differential movement between them. However, since the cap is snap-fitted onto the pressure plate, any temperature differential between the two usually allows the parts to readily slide along that fitting. An expansion joint in the cap may be required, depending on the overall length, to allow for any differential movement between them.
Q
Has there been any research on how steel curtain wall systems perform for ballistic blast resistance?
A
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No ballistic or blast-resistance testing has been completed to date for SteelBuilt Curtainwall® Systems, but in projects where analytical calculations have been done, the steel performs at an acceptable level. As an example of steel’s performance, the portion of the Pentagon that came under attack on 9/11 had just completed a remodel with steel-framed windows from another manufacturer that demonstrated the effectiveness of such an installation. Once the plane penetrated the exterior wall and the jet fuel ignited, the steel windows and their glazing remained in place as designed.
Q
What testing has been performed on the steel systems?
A
SteelBuilt Curtainwall Systems have been subjected to an extensive array of tests addressing air leakage, water penetration and other factors. These include:
ASTM E283-04: Standard Test Method for Determining Rate of Air Leakage Through Exterior Windows, Curtain Walls and Doors Under Specified Pressure Differences Across the Specimen
ASTM E547-00: Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors and Curtain Walls by Cyclic Static Air Pressure Difference
ASTM E331-00: Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Air Pressure Difference
ASTM E330-02: Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylights and Curtain Walls by Uniform Static Air Pressure Difference
The rolled profiles have undergone additional computer thermal modeling in accordance with:
NFRC 100: Procedure for Determining Fenestration Product U-Factors ()
NFRC 200: Procedure for Determining Fenestration Product Solar Heat Gain Coefficients at Normal Incidence ()
Q
What are the typical [perimeter] details for a steel curtainwall system?
FAQs — VS1 Curtain Walls by Innovation Glass
FAQs
Explore common questions about our aluminum, glass, timber, and steel curtain wall systems.
General FAQs
Common questions about VS1 and Innovation Glass
Q • What services does Innovation Glass offer?
A • Pre-construction design support, engineering, system fabrication and supply, project management, product development, and technical support.
Q • What specific engineering services does Innovation Glass offer?
A • We offer PE-stamped calculations for the VS1 system (always included), glass, embed anchors, thermal, seismic, acoustic, bomb blast, large missile impact.
Q • How does VS1 perform thermally?
A • VS1 offers best in class thermal performance compared to any other curtain wall system in the market. Please contact us for a copy of the official thermal report.
.18 U-Value
with triple IGU glass
Q • What is the largest panel of glass you can support? How thick can the glass be?
A • No size constraints. Theoretically a 10’-10” by 75’ glass panel (the maximum glass available); standard fittings can support glass panels up to 150 sq. ft; custom fittings can accommodate larger glass sizes. Up to 3” thick with standard fittings; thicker glass would require custom fittings.
Q • Does Innovation Glass provide the face glass as part of your package?
A• No, we do not. Our installation partner sources the glass through their normal and preferred supply chain. We also exclude the face glass to save the owner from paying an extra markup.
Q • Does Innovation Glass include doors in your package?
A • No. Our glazing contractor partners source these items. Any door hardware can be accommodated by VS1.
Q • Do you offer cladding material?
A • No, but VS1 aluminum can readily accommodate cladding supplied by others if desired.
Q • Can VS1 integrate with automatic sliding doors?
A • Yes, we can integrate with any door system. Innovation Glass provides the rough portal opening, usually in the form of a ¾” thick aluminum portal plate. We exclude doors from our package, so you can specify whichever product you like and the installer will buy it. We then coordinate with the door manufacturers during shop drawing phase.
Q • Will there be field fabrication required by the glazing contractor?
A • No. All VS1 components deliver fully fabricated and finished, and perimeter channels are typically shipped in stock lengths to allow the glazing contractor to correct for field tolerances.
Q • Can VS1 support external sunshades?
A • Yes, VS1 uses through-the-joint T-brackets for attachment of louvers and sunshades.
Q • Can Innovation Glass fulfill a Buy-America clause?
A • Yes, the VS1-A, VS1-T, and VS1-S systems can be fully sourced domestically in the US. Unfortunately, due to supply chain limitations, the structural glass fin component of VS1-G cannot be sourced from the US, so Innovation Glass imports them from Europe.
VS1-A FAQs
Common questions about our aluminum curtain wall system
Q • What is VS1-A’s largest vertical span?
A • VS1-A can span 65’ with no intermediary steel support structure.
Q • Can the shape of the VS1-A mullion be customized?
A • Yes. The design team can create their own original section which Innovation Glass will add to its growing mullion library.
Q • How does the VS1 all-glass corner work?
A • Vertical loads from the corner glass panels are supported by a corner tension rod or corner 1”x1” tube; lateral forces are transferred around the corner via structural silicone. The tension rod option requires the vertical corner glass edges to be offset while the corner tube detail allows standard glass edges to be used.
Q • What finishes does Innovation Glass provide?
A • Paint and powder coat. While paint is more common, we recommend powder as it is more cost effective and environmentally friendly.
Q • Can you accommodate a two-hour slab edge fire separation for multi-story facades?
A • Yes, we offer several engineered judgement details to achieve this.
Q • What is the mullion deflection limit applicable to long span VS1 facades?
A • 1) L/175 for spans up to 20ft, 2) L/140 for spans 20ft to 30ft, and 3) L/110 for spans 30ft to 65ft+
Q • How much does VS1 weigh on average?
A • The weight of a VS1 wall varies depending on mullion profile and glass makeup, but typically the combined weight of the installed VS1 system and face glass is 15 lbs./sq. ft.
Q • Does VS1 incorporate a weep or pressure equalized system for water management?
A • No, VS1 is a barrier system with a silicone weather seal; the system has been extensively mock up tested to validate this strategy; existing VS1 facades are performing without issues.
Q • Can the VS1 mullion be flipped to the exterior of the façade?
A • Yes; designers are free to alternate the position of the mullions at the exterior and interior in the same facade (for instance at a return wall).
Q • Does VS1 require external patch fittings?
A • No, VS1 has the option of incorporating toggle fittings that engage recessed channels in the IGU, resulting in a flush “no exterior metal” façade aesthetic. We also offer the toggle fitting strategy using cassette channel bonded to the inside surface of glass, which allows the use of standard IGUs.
Q • How do you deal with waterproofing issues at the base of a top hung wall?
A • We detail the expansion joint to be at the first horizontal glass joint so that the bottom panel is dead loaded to the sill channel; this eliminates vertical movements at the sill condition.
VS1-G FAQs
Common questions about our glass fin curtain wall system
Q • What is VS1-G’s largest vertical span?
A • VS1-G can span up to 59’ with no intermediary steel support structure. This can be done with one continuous un-spliced glass fin.
Q • Does VS1-G use the same fittings as VS1-A?
A • While it is possible to do so, our standard approach for VS1-G walls utilizes direct SSG between fin and face glass.
Q • Does VS1-G use spider fittings?
A • No. All VS1 systems use through-the-joint fittings that do not require holes to be drilled through the face glass. Standard glass panels can be used.
Q • Does VS1-G require laminated glass fins?
A • Yes. It is standard practice to use laminated structural glass fins. At a minimum, 2-ply is required, but the typical VS1-g fin is 3-ply construction with a SG interlayer.
Q • Who supplies the glass fins?
A • Innovation Glass. Because the fin is the structural element supporting the facade, Innovation Glass supplies them.
VS1-T FAQs
Common questions about our timber curtain wall system
Q • What is VS1-T’s largest vertical span?
A • VS1-T can span up to 40’ with no intermediary steel structural support.
Q • Can VS1-T be flipped to the exterior like the aluminum system?
A • It is not recommended. Given the different material properties and code requirements, it is not advised to have structural wood on the exterior of the façade.
Q • In what species is VS1-T available?
A • VS1-T is offered in two softwoods that are domestic to the US: southern yellow pine and Douglas fir. Innovation Glass can also source a beech hardwood from Germany that is five times stronger than most softwood options.
Q • How does Innovation Glass handle fire safety with a timber mullion?
A • We typically comply with the glulam fire safety requirements outlined in an individual project specification, which tend to differ. VS1-T can be delivered with an intumescent fire retardant to resist flame spread and achieve a specified UL rating.
Fire safety can also be implemented through analysis by designing the glulam section to be larger than may be needed structurally. Because glulam burns at a constant rate from the outside perimeter inwards, you can theoretically control how long a given glulam beam can withstand a fire.
VS1-S FAQs
Common questions about our steel curtain wall system
Q • Do you provide custom steel systems?
A • Yes. True to its name, Innovation Glass has its roots in solving complex designs with custom approaches, including Steel Facades, Specialty Steel Structures, Tension Based Structures, and All-Glass Structures. The Innovation Glass mission has always been to break new ground and seek inventive solutions to complex challenges.
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