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Glossary
Plain-language definitions of the aluminium building-envelope terms used across our guides.
- curtain wall
- A non-loadbearing aluminium-framed facade that hangs continuously in front of the floor slabs, carrying only its own weight and wind load back to the structure.
- In plain terms: glass-and-aluminium wall hung in front of the floor slabs
- dimensional stability
- A material's resistance to changing shape — warping, swelling, or shrinking — as temperature and humidity vary.
- In plain terms: resistance to warping and swelling
- fenestration
- The arrangement of windows, doors, and other glazed openings in a building envelope — and the assemblies that fill them.
- In plain terms: windows and doors
- glazing
- The glass (often insulated double or triple units) installed in a frame, plus the way it is secured and sealed.
- In plain terms: glass and its framing
- mullion
- A vertical structural member of a framed glazing system that separates and supports adjacent glass or panel units.
- In plain terms: vertical framing between panels
- NAFS
- The North American Fenestration Standard (AAMA/WDMA/CSA 101/I.S.2/A440) that rates windows, doors, and unit skylights for structural, water, and air performance. Curtain wall and window wall fall under "Other Fenestration Assemblies," not its class ratings.
- In plain terms: North-American window-and-door standard
- performance class
- A NAFS rating (R, LC, CW, AW) for windows, doors, and skylights that signals the product's intended use and minimum performance level. Does not apply to curtain wall or window wall.
- In plain terms: NAFS window-and-door rating letter
- performance grade
- A specified performance target (e.g. design pressure) that a fenestration assembly — including curtain wall and window wall — must be tested to meet for its location and exposure.
- In plain terms: design-pressure target a unit is tested to
- spandrel
- The opaque area of a facade — typically an insulated, back-painted glass or metal panel — that conceals the floor slab, ceiling plenum, or structure between vision glass.
- In plain terms: opaque panel hiding the floor edge
- thermal break
- A low-conductivity barrier (usually polyamide) set between the inside and outside of an aluminium frame to slow heat transfer through the metal.
- In plain terms: insulating barrier inside the frame
- thermal bridge
- A spot where a conductive material (like a concrete slab edge or unbroken metal) bypasses the insulation, letting heat escape and risking condensation.
- In plain terms: heat escaping through the structure
- transom
- A horizontal structural member of a framed glazing system, running between mullions to separate and support stacked glass or panel units.
- In plain terms: horizontal framing between panels
- U-value
- A measure of how readily heat passes through an assembly (W/m²·K) — the lower the number, the better insulated. Reported both at centre-of-glass and at the whole-assembly level.
- In plain terms: heat-loss rate
- window wall
- An aluminium glazing system installed between floor slabs, so each unit sits on the slab below and tucks under the slab above — fabricated and shipped as punched or stacked units.
- In plain terms: glazed wall set between the floors