The general layout of the guide specification&#;s three parts is as follows.
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Part 1: General
This part contains descriptions of product, scope of the system, and a list of work to be included in the specification. It further references additional items that should be specified, such as:
Performance and testing requirements
During the design and development stage, all curtain wall systems should be tested for the leakage of air infiltration, water penetration, and for structural performance (including frame deflection limits) at the wind loads applicable for the building site. This is one of the most important parts of curtain wall specifications. Testing is the only way in which certain capabilities of a wall, such as resistance to air leakage or water penetration, can be determined. The sequence of testing should be specified so the effect of exposure to test conditions on other performance parameters can be accurately assessed (for example, repeat water penetration resistance tests after subjecting the specimen to design loads). Any modifications to the design resulting from the testing must be communicated to all interested parties and fully documented to ensure it is incorporated fully into the design.
Particularly for custom designs, a preconstruction mockup test should be scheduled well in advance of the final production schedule for a building, affording ample opportunity to make corrections relatively easily and less expensive. If a mockup is deemed necessary, the guide specification provides optional language for specifying mockup testing including what parts of the system are to be represented and where the mockup is to be erected. Compliance with ASTM E, Standard Practice for the Specification and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems, for procedures and documentation required for laboratory mockups should also be required.
Deflection of glass-supporting frame members
The more the frame deflects under the load, the more stress is placed on the glass and the greater the likelihood of breakage. The typical design convention is to limit frame member deflection to maximum of L/175 of the unsupported span length (L) of up to 4 m (14 ft) in length, maximum L/240 + 6.4 mm (250 mils) at spans over 4 m; or 2L/175 at unsupported cantilevers, except when a plastered surface or dry wall is subjected to bending, the deflection shall not exceed L/360 of the span.
Uniform structural loads and testing requirements
Uniform load structural tests of the curtain wall system (in addition to deflection tests) should be conducted per ASTM E330, Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylights, and Curtain Walls by Uniform Static Air Pressure Difference, subjecting the system to inward and outward acting uniform loads equal to 1.5 times the inward and outward acting design wind pressures.
Other specific mandatory requirements in this section deal with:
Part 2: Product
The product section describes the framing material (metals, finishes, and protective coatings), glazing materials, system configuration, and components. Fabrication requirements also should be specified to include requirements for the desired degree of factory assembly and/or glazing, mechanical fastening, and sealing of joints. It is important for all to understand the anticipated level of factory assembly and/or glazing to avoid unexpected delays in the field or costly charge backs. Additionally, special conditions such as drywall pass through glazed units need to be carefully detailed in the specifications and construction documents.
Part 2 of the guide specification lists third-party specifications like ASTM, AISC, American Iron and Steel Institute (AISI), to which different components (such as sheet and plate, extrusions, and welding rods) must conform, for aluminum, carbon steel, stainless steel, and (optionally) special alloys.
Here&#;s what you need to know about steel curtain wall systems to get started on your next project.
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Test standards for curtain walls vary depending on the project and required codes. Below are some of the most common test standards for curtain wall applications:
The rolled profiles used in SteelBuilt Curtainwall® Systems have undergone additional computer thermal modeling in accordance with:
Yes. Fire-rated curtain walls are available that are tested to ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials, and Underwriters Laboratories (UL) 263, Fire-resistance Ratings. Receiving classification as non-directional fire-resistance-rated construction (meaning they can maintain the same fire-rating from both sides), they can exceed 25 percent of the total wall area. This helps to greatly expand design freedom, as products without this classification, such as &#;opening protectives,&#; cannot exceed 25 percent of the total wall area.
To achieve such a high level of defense, fire-rated curtain walls incorporate fire-resistive glass and framing. It is important to note all curtain wall system components are required to be tested as one assembly. This includes the glass, exterior cover caps, back framing members, seals, fire-safing, etc. When successfully tested, the designer is assured the entire system will block the transfer of flames and smoke, as well as radiant and conductive heat, for the duration of their given fire rating. This is critical since the International Building Code (IBC) requires all elements within a fire-resistive glazing assembly to provide the same category of fire resistance and carry the minimum fire rating as stated in the code.
While fire-rated curtain walls are often evaluated on performance, aesthetics are also a key consideration. Systems that use inherently heat-resistant carbon steel and incorporate precise European engineering lend to sleek, narrow profiles. Architects can use them to create expansive, code-compliant fire-rated glass curtain walls, beautiful atriums, and divided interior spaces where the glazing is featured more prominently than in past systems.
Learn more about fire-rated curtain wall solutions from TGP.
The LEED green building rating system has forever altered North American construction practices. Since adoption, LEED has aimed to reduce greenhouse gas emissions, water consumption and waste production. It has also enhanced the way facilities are operated, reducing energy use and supporting occupant wellbeing through improved views and access to daylight.
Today, steel curtain wall systems can help design teams meet LEED requirements by earning points in the following categories:
Energy and atmosphere (EA)
LEED&#;s stated purpose in this category is &#;to achieve increasing levels of energy performance beyond the prerequisite standard to reduce environmental and economic harms associated with excessive energy use.&#;
Steel has a lower thermal conductivity than aluminum, which means it transfers heat at a slower rate. This can lead to decreased energy consumption. Combined with the proper glazing, a steel curtain wall system can also reduce solar heat gain to help lower cooling costs.
Indoor environmental quality (EQ)
LEED has set a high bar for daylighting credits, requiring natural light in as much as seventy-five percent of interior spaces. This is a natural fit for steel curtain wall systems since they allow for tall free spans of glass. For example, the continuous steel elements can handle up to 40-foot free spans in a single member without splicing. Such uninterrupted stretches of glazing maximize the amount of natural daylight that can reach deep into a building&#;s interior.
With respect to credits for quality views, LEED stipulates that there must be &#;a direct line of sight to the outdoors via vision glazing for 75 percent of all regularly occupied floor area.&#; Here again, steel offers advantages. For non-fire-rated assemblies, the steel mullions in a curtain wall system are available in a variety of sizes and shapes, such as box, I-beams, and T-shapes. Compared with aluminum&#;s basic &#;box&#; back counterpart, steel T-shapes are slimmer and allow for more unobstructed views.
By minimizing the amount of framing needed in the system, steel curtain walls also help preserve sightlines. This allows for visual communication and connectivity between the interior and exterior environments.
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