A curtain wall (also written curtainwall) is a non-load-bearing exterior wall hung off the outside of a building’s structure. It carries its own weight and resists wind, but takes none of the building’s floor or roof loads. Most curtain walls are aluminium frames filled with glass or panels, anchored to the edges of the floor slabs and running continuously past them rather than sitting between them.
In the UK the system is often called curtain walling.
How a curtain wall works
Wind pressure and the wall’s own weight pass from the glass into the framing, then through anchors into the slab edges or spandrel beams. The anchors allow for movement: floors deflect, the building sways and the aluminium expands and contracts with temperature. The system is also designed to manage water, usually with gaskets as the outer seal and internal drainage and weep holes to let any water that gets past them back out.
Main components
- Mullions: the vertical framing members. See mullion.
- Transoms (horizontals): the horizontal members between mullions.
- Vision glass: usually insulated glass units, sometimes low iron glass for clarity.
- Spandrel panels: opaque panels that hide the slab edge and ceiling space. See spandrel panel.
- Anchors: steel clips or brackets connecting the wall to embeds or the slab edge.
- Pressure plates and caps, or structural silicone: hold the glass in the frame.
Types of curtain wall
| Type | How it is built | Typical use |
|---|---|---|
| Stick-built | Mullions and transoms are installed piece by piece on site, then glazed | Low and mid-rise buildings, podiums, smaller areas |
| Unitized | Panels are assembled and glazed in a factory, then lifted and hooked onto anchors | High-rise towers, tight schedules, large repetitive facades |
Glazing can be captured (held by pressure plates and visible caps on all sides) or structurally glazed (bonded with structural silicone so the outside face shows only glass and joints). Many systems mix the two.
Curtain wall vs window wall vs storefront
- Curtain wall: passes in front of the slabs as one continuous skin.
- Window wall: sits between floor slabs, with a slab edge cover; common in residential towers.
- Storefront: a lighter framing system, usually at ground level and set between floor and structure above.
Installation and QA tips
- Survey slab edges and embeds early; out-of-tolerance edges are a common source of delay.
- Build and test a mockup before production, and confirm details with the supplier’s shop drawings.
- Plan field water testing on installed areas. Specifications often call for AAMA 501.2 or ASTM E1105 tests; follow what your project specifies.
- Coordinate the slab edge firestop and insulation behind the spandrel with the trades responsible.
- Protect installed glass and finishes from welding spatter, concrete and paint.
- Plan access: cranes and hoists for unitized panels, a swing stage for sealant and repairs.
Related templates and guides
- Curtainwall quality control checklist
- Interface guidelines for curtainwall
- Safety meeting: glazing
- Basics of building envelope construction
Frequently asked questions
What is the difference between a curtain wall and a window wall?
A curtain wall hangs off the outside of the floor slabs and runs continuously past them. A window wall sits between the slabs, floor to ceiling, and the slab edge is covered with a separate cover or panel. Window wall is generally simpler and cheaper; curtain wall gives a continuous glass face.
Is a curtain wall structural?
Not in the sense of carrying the building. A curtain wall supports its own weight and resists wind and other loads on its face, then transfers those loads to the building structure through anchors. It carries no floor or roof loads, which is why it can be thin and mostly glass.
What is a curtain wall made of?
Most modern curtain walls use extruded aluminium framing with thermal breaks, insulated glass units, and spandrel panels at the slab edges. Infills can also be metal panels, stone or terracotta. Gaskets, sealants and pressure plates or structural silicone hold the infills in the frame.
Is it curtainwall or curtain wall?
Both spellings are used. ‘Curtain wall’ is more common in general writing and dictionaries, while ‘curtainwall’ as one word appears in many specifications, shop drawings and on site. They mean the same system.
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