Moisture intrusion
Advanced steel curtain wall assemblies resolve an important performance challenge—preventing water in the glazing cavity from coming into direct contact with the steel frame. By incorporating a continuous gasket across the full width of the steel frame, they can provide sufficient protection against dynamic and static water penetration, and reduce the potential for corrosion.

For example, steel frames with continuous gasketing keep water off the tops of insulated glass (IG) units and direct it to the verticals. Installers then must ensure performance by sealing the lapped gasket joints at horizontal-to-vertical connections to prevent water intrusion to the steel back members and interior occupied spaces.

As an added benefit, these systems do not require zone damming at each glazed lite to help manage water flow within the system, as is typical with aluminum pressure plate systems. The full gasketing fabrication method without zone damming still provides a water penetration resistance of 718 Pa (15 psf), meeting ASTM E331, Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Air Pressure Difference.

To ensure greater protection from corrosion once the building is completed, some steel systems employ more-conventional aluminum or stainless steel cover caps and pressure plates to retain the glass to the framing. They rely on self-sealing fasteners that penetrate the glazing, while simultaneously blocking access for water penetration. When using structural silicone glazing, sealants specific to the application are available. They hold the glass to the framing in lieu of pressure plates and covers, as is typical with captured curtain wall systems.

Installers can also place watertight weather seals around the perimeter of the framing. The seals are made to gaskets at the back of the glazing pocket. Typically, they are made to special extrusions or to perimeter details in plane with the glass instead of to the framing. By placing perimeter seals in front of the steel, the installer eliminates any chance of water contacting the material behind the seal.

Even though stainless steel has improved resistance against corrosion, many features are the same when using stainless steel for the frame gasketing. The edge seal details are similar for either material, and both can offer the same air- and water-penetration resistance.

To further simplify and standardize fabrication and installation for both materials, while still meeting the higher performance criteria of modern curtain wall construction, steel curtain wall system suppliers have developed all component parts to the point where a complete system is often available, including:

• connection detailing and hardware;
• gasketing;
• exterior pressure plates and cover caps; and
• complementary door and entry systems, as well as detailing.

Due to the full gasketing across the face of the systems at the back of the glazing pocket, some steel curtain wall systems can provide even greater protection against the elements. For example, water resistance can be as much as 25 per cent greater in an off-the-shelf steel curtain wall assembly than with a conventional extruded aluminum curtain wall. Additionally, air penetration is almost non-existent in steel curtain walls due to the full gasketing, testing to as low as 0.1 cf/sf of wall (per ASTM E283, Standard Test Method for Determining Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen, at 298.7-Pa [6.24-psf] pressure differential).