Face-Capped or Structurally Glazed Curtain Wall?

Clarify the terminology

Vertical mullions and horizontal transoms form the primary aluminum grid of many curtain walls. In Iranian project language, these members are also commonly called *lamels*. A face cap is the visible exterior cover installed over a pressure plate that mechanically retains the glass or infill.

A facade can therefore use mullions and transoms whether its external appearance is fully capped, semi-capped or structurally glazed. Asking “lamel or face cap?” mixes the support member with the exterior retention style. The procurement documents should name the complete system.

The load path remains essential

Wind pressure travels from glass to its supports, then through transoms, mullions and anchors to the building structure. Glass dead load is carried at specified support points. Aluminum sections, connections and glass are selected for span, module geometry, design pressure and allowable movement.

In a face-capped system, a pressure plate and fasteners provide mechanical retention at the supported edges; the snap-on cap completes the exterior appearance. In a structurally glazed system, an engineered silicone joint may transfer prescribed loads at selected edges while separate devices, blocks or retained edges perform other support functions. The exact arrangement must follow the approved system design.

Face-capped curtain wall

Face caps create a visible grid and make the facade module legible. They offer a well-established drained assembly and can simplify external inspection and pane replacement. Cap shapes and colors can coordinate with fins, floor lines and other facade elements.

The projecting grid may collect dust and influence cleaning. Its architectural character is more expressed than a flush glass plane. Cap joints, pressure-plate continuity, fastener cover and drainage intersections still require careful fabrication and installation.

Structurally glazed and cap-free appearances

Reducing external metal can create a calm, continuous reflective surface. It also makes joint width, sealant tooling, glass alignment, coating consistency and facade tolerances more visually prominent.

Structural silicone glazing requires approved substrates, joint dimensions, bite, surface preparation, compatibility testing, batch control and curing procedures. A weather seal is not automatically a structural seal. Fabrication and site replacement should follow the system supplier's documented process.

Semi-capped arrangements

Some designs cap only vertical or only horizontal joints. This creates directional emphasis while retaining mechanical pressure components on one axis. It can bridge the visual gap between a full grid and a flush facade, but it introduces transition details that must preserve drainage and load transfer.

The cap direction should be decided early. Changing it after architectural approval can alter glass sizes, retainers, joint details, quantities and the estimate.

Water management

Good weather performance comes from continuous internal seals, pressure-moderated cavities and open drainage paths—not simply from having more visible aluminum. End dams, baffles, gasket corners and transom-to-mullion seals must be installed as designed.

For exposed or consequential facades, agree laboratory or field water testing, specimen size and acceptance criteria before procurement. A realistic mock-up can test corners, perimeter interfaces and opening vents that are absent from a catalogue section.

Maintenance and replacement

Ask how each typical and corner pane is removed, supported and reinstalled. Face caps offer an obvious mechanical access route. Structurally glazed panes may require specialist sealant removal, temporary restraint and factory or site curing controls.

Cleaning access, seal inspection and safe working zones should be considered with the architecture. A system that cannot be maintained from the planned access equipment is not fully designed.

Compare cost on the same basis

Include mullion series and approximate aluminum quantity, module sizes, glass processing, surface finish, anchors, opening vents, corners, sealants, access, testing, replacement strategy and warranty. A cap-free elevation may use less visible metal yet need more processed glass and stricter factory controls.

Select the facade after structural analysis, drainage detailing and an approved visual sample. Face-capped, semi-capped and structurally glazed options can all perform well when the complete assembly—not the label—is engineered and verified.