Glazing Glossary
Plain-language definitions for glazing and glass industry terms.
A
- Annealed glass
- Float glass in its standard, unprocessed state — cooled slowly to relieve internal stresses but not further treated by toughening or laminating. Breaks into large, sharp shards and is not classified as safety glass under AS 1288.
- Argon fill
- An inert gas used to fill the sealed cavity of a double glazed unit (IGU) in place of air. Argon has lower thermal conductivity than air, improving the unit's U-value by approximately 0.2–0.4 W/m²K.
- Arch glazing
- A glazing panel with a curved upper section — either a full semicircle (full arch) or a partial curve (segmental arch). Arch panels must be ordered with width and rise dimensions.
- AS 1288
- The Australian Standard for the selection and installation of glass in buildings. Specifies which glass type and thickness must be used based on panel size, wind load zone, human impact risk, and application. Mandatory for all building work in Australia.
B
- Balustrade
- A barrier system used on stairs, balconies, mezzanines, and around pool areas to prevent falls. Glass balustrades use structural glass selected in accordance with AS 1288 and the NCC.
- Bite
- The depth to which the glass edge sits inside the frame rebate. AS 1288 specifies minimum bite depths: typically 12mm for single glazed panels and 16mm for double glazed units.
- Breakout
- The uncontrolled fracture of a glass pane during or after installation — typically caused by thermal stress, frame movement, edge damage, or incorrect sizing. Breakout of annealed glass is particularly dangerous as it produces large, sharp shards.
C
- Clearance
- The gap between the glass edge and the frame rebate, allowing for thermal expansion and frame irregularities. Standard clearance is 1.5mm per side (3mm deduction per dimension for single glass).
- Cullet
- Waste or recycled glass returned to the furnace as raw material for new glass production. Float glass manufacturing typically uses 20–30% cullet.
D
- Dead load
- The permanent self-weight of a glass panel. Dead load determines the required size and position of setting blocks at the base of the frame.
- Deflection
- The bending of a glass panel under lateral load (typically wind pressure). AS 1288 limits maximum deflection to span/60 or 20mm (whichever is less).
- DGU
- Double Glazed Unit. See IGU.
- Dry glazing
- A glazing method that uses pre-formed rubber or EPDM gaskets to retain and seal glass in a frame, rather than wet-applied silicone.
E
- E-value
- See Emissivity. Sometimes used interchangeably with emissivity in the glazing industry to describe a surface's ability to emit thermal radiation. A lower E-value indicates a more reflective surface and better thermal performance.
- Emissivity
- A measure of a surface's ability to absorb and re-emit infrared (heat) radiation, expressed as a value between 0 and 1. Standard clear glass has an emissivity of approximately 0.84. Low-E coatings reduce this to 0.10–0.20.
F
- Fixed light
- A non-opening window panel. Fixed lights can accommodate larger and heavier glass than most openable window systems.
- Float glass
- Glass manufactured by the Pilkington float process — molten glass is floated on a bath of molten tin, producing flat sheets with optically clear, parallel surfaces. The starting material for virtually all construction glass products.
- Fritted glass
- Glass with a ceramic enamel pattern (frit) applied and fired onto one surface. Used for solar control, visual privacy, and bird-strike prevention.
G
- Glazing bead
- A thin strip of timber, aluminium, or PVC fixed to the frame to retain the glass in the rebate.
- Glazing compound
- A putty-like material traditionally used to bed and seal glass in timber frames. Made from linseed oil and whiting (calcium carbonate). Has largely been replaced by modern silicone sealants and foam tape systems, but is still used in heritage restoration work.
- Glazing tape
- A compressible foam or butyl tape applied to the rebate bed before glass installation. Provides cushioning and seals against air and water infiltration.
- Grade A safety glass
- The classification under AS 1288 for glass that meets human impact requirements. Both toughened glass (small blunt fragments) and laminated glass (fragments held by interlayer) qualify as Grade A.
H
- Hard coat
- A Low-E coating applied during the float manufacturing process while the glass is still hot. Durable enough for exposed glass surfaces.
- Heat-strengthened glass
- Glass partially heat-treated to be stronger than annealed glass but not as strong as fully toughened. Not classified as safety glass under AS 1288.
I
- IGU
- Insulated Glass Unit — the technical name for a double (or triple) glazed unit. Expressed as glass/spacer/glass in millimetres (e.g. 6/12/6 = two 6mm panes with a 12mm spacer = 24mm total thickness).
- Interlayer
- The bonding layer between glass panes in laminated glass. The most common material is PVB (polyvinyl butyral). Acoustic PVB uses a softer formulation that provides additional sound damping.
K
- Krypton fill
- A heavier inert gas used in high-performance double and triple glazed units. Krypton has lower thermal conductivity than argon but is significantly more expensive.
L
- Laminated glass
- Two or more glass panes bonded together with a PVB or similar interlayer under heat and pressure. When broken, the interlayer holds fragments in place. Meets AS 1288 Grade A safety requirements.
- Low-E glass
- Glass with a low-emissivity metallic coating that reflects infrared heat while transmitting visible light. Used in double glazed units to improve U-values and SHGC.
- Low-iron glass
- Float glass manufactured with minimal iron oxide content, producing a virtually colourless pane without the green tint of standard float glass. Also sold as Optiwhite, Starphire, and Diamant.
M
- Monolithic glass
- A single pane of glass, as opposed to a laminated or double glazed assembly.
N
- NCC
- National Construction Code — Australia's primary building code, which adopts AS 1288 by reference for glazing requirements.
O
- Obscure glass
- Glass with a textured, frosted, or etched surface that diffuses light and reduces visibility. Common in bathrooms, entry sidelights, and privacy screens.
P
- PVB
- Polyvinyl butyral — the most common interlayer material in laminated glass. Provides good adhesion, impact resistance, and UV absorption.
R
- Rebate
- The stepped groove or channel in a window frame that receives the glass edge. When measuring for replacement glass, always measure the full rebate opening, not the visible glass area.
S
- Safety glass
- Glass manufactured to reduce the risk of injury when broken. In Australia, Grade A safety glass (toughened or laminated) is required by AS 1288 in human impact zones.
- Setting block
- A small block of EPDM rubber or neoprene placed under the glass at the base of the frame to support the panel's dead load and prevent direct glass-to-frame contact.
- SHGC
- Solar Heat Gain Coefficient — a measure of how much incident solar energy passes through glass into the building. Expressed as a number between 0 and 1; lower values mean less solar heat gain.
- Silicone (structural)
- A high-modulus, two-part silicone adhesive used to bond glass to a structural substrate such as a curtain wall mullion without mechanical fixings. Must be engineered and installed in accordance with the manufacturer's structural calculations.
- Silicone (weatherseal)
- A low-modulus, one-part silicone sealant applied to exposed glass-to-frame joints to prevent water and air infiltration. Flexible enough to accommodate thermal movement. Not suitable for structural bonding applications.
- Soft coat
- A Low-E coating applied post-manufacture in a vacuum chamber. Provides superior thermal performance compared to hard coat but must be protected inside an IGU.
- Spacer
- The component in a double glazed unit that separates the two glass panes and seals the cavity. Warm-edge spacers have lower thermal conductivity than traditional aluminium spacers.
- Spandrel glass
- Opaque glass used in curtain wall construction to conceal structural elements such as floor slabs, beams, and insulation between vision panels. Typically toughened and coated or backed with an opaque paint or film.
T
- Tinted glass
- Float glass manufactured with metallic oxides added to the glass batch to produce a body colour — commonly bronze, grey, green, or blue. Tint reduces solar heat gain and visible light transmission. Unlike reflective coatings, the tint is throughout the glass thickness.
- Toughened glass
- Float glass heat-treated by heating to approximately 620°C and rapidly quenching. Approximately four times stronger than annealed glass. When broken, shatters into small, blunt fragments. Cannot be cut or drilled after toughening. Also called tempered glass.
U
- U-value
- Thermal transmittance — a measure of heat flow through glass due to temperature difference. Expressed in W/m²K; lower values mean better thermal insulation. Standard 6mm glass: ~5.8 W/m²K. Standard 6/12/6 IGU: ~2.7 W/m²K.
W
- Warm-edge spacer
- A double glazed unit spacer made from materials with lower thermal conductivity than aluminium. Reduces the 'edge effect' heat loss around the perimeter of an IGU.
- Wet glazing
- A glazing method using wet-applied sealants — silicone, polyurethane, or traditional putty — to bed and seal glass in a frame.
- Wind load
- The lateral pressure exerted on a glass panel by wind. AS 1288 provides tables for determining minimum glass thickness based on panel size, wind region, terrain category, building height, and shielding.