Curtain Wall Components: What Are the Main Parts?

The glass and framing are the most visible parts of a curtain wall, but they are only part of the assembly. Main curtain wall components include mullions, transoms, anchors, infill panels, glazing supports, gaskets, sealants, drainage provisions, and thermal breaks. Some support the glazing and transfer loads, while others manage water, seal joints or reduce heat transfer.

An elevation shows the panel layout and framing lines, but section drawings reveal how the components connect behind the facade. This article focuses on conventional framed aluminum curtain walls, with differences between mechanically retained glazing and structural silicone glazing noted where relevant.

Main Curtain Wall Components and Their Functions 

Start with the location and function of each component group. A supplier's elevation may clearly communicate panel proportions, while sections reveal the supports, seals, and connections behind them.

For a detailed example, the WBDG curtain wall head detail illustrates how framing, anchors, glazing seals and building enclosure layers meet at a curtain wall connection.

Curtain Wall Framing: Mullions, Transoms and Anchors 

Mullions and Transoms

Mullions generally run vertically, while transoms run horizontally between them. Together, they define openings for glass, spandrel panels and other infill. Their connections help transfer the loads assigned to them through the framing toward its supports.

The frame layout therefore affects more than the facade pattern. Changing a transom position can alter glass dimensions and supporting arrangements. Although two elevations may look similar, their framing depths, internal reinforcement and connections can differ. Visible frame width alone gives an incomplete picture of the assembly.

Anchors, Brackets and Frame Connections

Anchors and brackets connect the curtain wall framing to the building structure. They bridge the distance between the facade line and its support points, commonly at floor slabs or structural steel.

These connections carry curtain wall loads back to the structure; the curtain wall does not support the building’s floors or roof. Depending on the design, connections also accommodate adjustment and specified movement. Frame splices join mullion lengths where required. Their appearance in a section explains how apparently continuous framing is assembled from separate members.

Under ASTM E330/E330M, structural testing evaluates the specified curtain wall specimen under uniform static air pressure. The standard does not establish the structural performance of adjacent building construction, so the supporting structure and its connections require separate consideration.

Glass, Infill Panels and Glazing Supports

Vision Glass and Spandrel Panels

Vision glass forms the transparent areas of a curtain wall, allowing daylight into the building and providing views outside. Insulating glass units (IGUs) are commonly used, with their construction selected according to project requirements.

Not every area of the facade needs to be transparent. Spandrel panels conceal floor edges, services and other construction, using opaque glass or metal infill panels with a coordinated backing assembly. From outside, the facade may appear to have a continuous glass finish, even though the vision and spandrel areas have different constructions behind them.

Metal infill also requires supporting and fixing arrangements compatible with the curtain wall system. Its thickness and edge construction may differ from the adjacent glass, so the same glazing details cannot simply be assumed to apply.

Setting Blocks and Glazing Retention

Glass needs support for its weight as well as a means of keeping it securely in the frame. Setting blocks sit beneath the glass, transferring its weight to the supporting framing and maintaining separation from metal surfaces.

In a typical pressure-plate configuration, the pressure plate mechanically retains the glass through the specified glazing arrangement. A cover cap clips over the assembly to provide the visible finish. The cap conceals the fixing; it does not hold the glass in place.

External pressure plates and caps are not used in every curtain wall. Structural silicone glazing (SSG) relies on a different retention arrangement at designated edges, and some systems combine captured and silicone-glazed edges. Simply removing the caps will not achieve the same result. A smoother exterior requires the appropriate glazing configuration.

Gaskets, Sealants and Drainage Paths

Gaskets and Sealants

Gaskets and sealants close joints around curtain wall glazing and framing, but they are used in different ways. Preformed gaskets, commonly made from materials such as EPDM, seal designated contact areas between glass and framing. Applied sealants are used at specified joints, including frame connections and perimeter interfaces.

Not every silicone joint serves the same purpose. Weather sealants help control air and water exposure at joints, while structural silicone in an SSG assembly also plays a role in retaining the glass. A visible silicone joint should not be assumed to provide structural support.

Sealing also extends beyond the glass edges. At the facade perimeter, the seals must connect with the adjacent enclosure construction to maintain the intended air and water control. Corners and frame intersections need attention as well, since separate gasket lengths meet at these points. Even with continuous-looking straight runs, those junctions remain part of the seal.

The performance of installed seals can also be assessed through field testing. AAMA 503-24 provides a method for evaluating air leakage and water penetration resistance in newly installed curtain wall systems under controlled test conditions.

Drainage Cavities, End Dams and Weep Holes

Seals are only part of how a curtain wall manages water. Many framed systems also provide drainage paths for incidental water that enters designated cavities. Frame channels collect this water and guide it toward outlets that discharge to the exterior.

End dams, where required, help contain water within the intended drainage route. Weep holes allow it to exit the framing, although their positions vary with the system design.

Some openings in pressure plates or covers are therefore part of the drainage arrangement, rather than gaps that need sealing. Blocking them with sealant can prevent water from escaping. Glazing supports must also be positioned without obstructing the drainage path.

Thermal Breaks and Spandrel Insulation

Thermal Breaks in Aluminum Framing 

Thermal breaks are insulating separators within aluminum curtain wall framing that reduce heat transfer between its interior and exterior parts. Depending on the system, they may separate framing sections or isolate an external pressure plate from the internal member.

A glass-only U-factor does not represent the thermal performance of the completed curtain wall. The NFRC Commercial Certification Program supports whole-product performance evaluation, accounting for the framing and glazing configuration rather than relying on the glass specification alone.

Spandrel Insulation and Backpans 

Behind opaque glass or metal spandrel panels, insulation helps reduce heat transfer through the infill area. A backpan may enclose the insulation and, depending on its detailing, contribute to the assembly’s air and moisture control.

Unlike thermal breaks within the aluminum framing, spandrel insulation addresses heat transfer through the opaque infill assembly. At floor edges, perimeter fire containment is a separate assembly; spandrel insulation does not replace it.

Conclusion

Identifying the main curtain wall components is relatively straightforward. The more useful distinction is how those parts are supported, connected and sealed within the selected assembly. Glass and metal infill may occupy similar openings, for example, but their fixing arrangements and surrounding details are not necessarily interchangeable. These differences need to be clear before drawings move into fabrication and installation.

For projects involving metal infill panels, PRANCE supports site measurement, detailed drawings and production. Contact PRANCE for a quotation on metal panels coordinated with your curtain wall design.

FAQs About Curtain Wall Components

Do Stick and Unitized Curtain Walls Use the Same Components?

Yes, stick and unitized curtain walls use similar component categories, including framing, infill panels, anchors, seals and drainage provisions. The main difference is how they are assembled. Stick systems are typically built progressively on site, while unitized systems use prefabricated modules. Their profiles, connections and sealing details are therefore not necessarily interchangeable.

Are Curtain Wall Components Interchangeable Between Systems?

No, curtain wall components are not automatically interchangeable, even when their dimensions appear identical. Profiles, gasket grooves, glazing pockets, fasteners and drainage routes must be compatible with the selected system. Using mismatched parts can affect glass retention, gasket compression and drainage performance. Replacement components should follow the system supplier’s requirements or undergo an appropriate technical review.

Can a Damaged Infill Panel Be Replaced Independently?

Yes, a damaged curtain wall infill panel can often be replaced individually, provided the glazing retention system allows removal and sufficient access is available. Mechanically retained panels and bonded glazing require different replacement procedures. The new panel must match the required dimensions and construction, remain compatible with existing supports and seals, and preserve the original drainage and joint details.