Float (annealed) glass: standard residential glazing where AS 1288 allows

TL;DR

Float glass (also called annealed glass) is the base flat glass product, made by floating molten glass on a bath of liquid tin to produce optically clear sheets with parallel surfaces and consistent thickness. Float is not safety glass: when it breaks, it breaks into long sharp shards. It can therefore only be used in residential applications where AS 1288:2021 does not mandate Grade A safety glass. Typical cases: standard windows above 500 mm sill height, picture-frame glazing, internal non-impact partitions, garage and workshop windows, and shop-fronts at the residential-commercial overlap. The volume Australian manufacturers are Viridian (BlueScope subsidiary, national), G.James Glass & Aluminium (Queensland-based, national distribution), and ACI Glass / O-I. Float glass also serves as the base substrate for the value-added glass products: it’s the material that becomes toughened glass (after thermal treatment), laminated glass (after lamination with interlayer), and Low-E energy-rated glass (after pyrolytic or sputter coating). The two specification calls: thickness (3, 4, 5, 6, 8, 10 mm common; thicker for larger panes per AS 1288 selection) and type (clear, tinted, Low-E coated, or the substrate for an IGU/insulated glass unit). Cost is materially lower than toughened or laminated; lead time is shorter (days vs weeks).

What it is

Float glass is manufactured by the Pilkington Float Process: raw materials (silica sand, soda ash, limestone, dolomite, recycled glass cullet) are melted at 1500°C, then floated as a continuous ribbon across a bath of molten tin. The smooth surface of the tin gives the glass its parallel surfaces and optical clarity. The ribbon is cooled at controlled rate (annealed) to remove internal stress and emerge as flat, rectangular sheets ready to cut.

The annealed state is what distinguishes float glass from toughened and laminated:

Annealed: internally stress-free, breaks into long sharp shards under impact
Toughened: internally stressed, breaks into small cubic safety fragments
Laminated: annealed (or toughened) panes bonded together with PVB interlayer; retains shape under impact

Float glass is the base substrate for almost all subsequent glass processing. Toughening, laminating, coating, and IGU assembly all start from a float glass sheet.

AS 1288 selection: where float glass is and isn’t allowed

AS 1288:2021 Section 5 sets selection rules by application and human-impact zone. Float glass is allowed where AS 1288 doesn’t require safety glazing:

Application	Float glass acceptable?
Standard window, sill above 500 mm	Yes (subject to size and thickness selection)
Picture-frame glazing in a non-impact area	Yes
Internal partition outside human-impact zones	Yes
Workshop / garage window, above 500 mm sill	Yes
Shop window (Class 3-9 building, not residential)	Yes (different rules apply)
Shower screen	No: toughened mandatory
Glazed door or side panel	No: toughened or laminated mandatory
Window with sill < 500 mm above floor	No: toughened or laminated mandatory
Balustrade	No: toughened or laminated mandatory
Low-level window adjacent to doorway	No: toughened or laminated mandatory
Roof skylight	Engineer-specified; typically laminated or toughened

Where float glass is not allowed, toughened glass or laminated glass is the substitution.

Thicknesses and sizing

Thickness	Typical residential application
3 mm	Picture frames, small windows, internal partitions
4 mm	Standard window glazing (small panes)
5 mm	Medium window panes
6 mm	Larger window panes, sliding doors (where AS 1288 allows non-safety)
8 mm	Large window panes per AS 1288 thickness selection
10-12 mm	Heavy windows, large openings, engineer-specified
15-19 mm	Specialty large-pane applications

AS 1288 Section 5 gives a thickness selection table by pane area and wind pressure. Larger panes need thicker glass. A 1.5 m × 1.5 m window in standard wind zone N1-N2 typically uses 4-5 mm float; the same window in N4+ uses 6 mm or larger.

Australian manufacturers

Brand	Range	Where supplied
Viridian (BlueScope subsidiary)	Full float range, value-added products (Low-E, tinted, IGU), the volume Australian manufacturer	National
G.James Glass & Aluminium	Full float range, with window-and-door fabrication integration	National (QLD-based)
ACI Glass / O-I (Owens-Illinois)	Bottle glass + flat glass (limited range)	Specialist supply
Stegbar / A&L	Window-and-door manufacturers; glass supplied through them	National

The float-glass market is concentrated among 2-3 manufacturers with merchant distribution. Glaziers typically order through a glass merchant who sources from these manufacturers and provides cutting and edge work.

Energy-rated variants

Standard clear float glass has a U-value of approximately 5.7 W/m².K and a solar heat gain coefficient (SHGC) of approximately 0.81 (most of the sun’s heat passes through). For NCC 2022 NatHERS energy compliance, residential windows in most climate zones need better thermal performance than plain float can deliver.

Energy-rated variants made from float-glass substrate:

Product	What it does	Typical use
Tinted float glass (green, grey, blue, bronze)	Reduces solar heat gain via absorption	Aesthetic + moderate energy benefit
Pyrolytic Low-E coating (hard coat, applied during float manufacture)	Reflects long-wavelength infrared; reduces U-value to ~3.5 W/m².K	Single-glazed windows where double-glazing is impractical
Sputter Low-E coating (soft coat, applied after float manufacture)	Reflects more infrared; U-value to ~1.5 W/m².K	Inside surface of insulated glass units (IGU)
IGU / Insulated Glass Unit (two panes separated by spacer with argon fill)	Adds thermal break; U-value ~1.0 to 1.8 W/m².K	Cool-climate residential, premium contemporary
Triple glazing (3-pane IGU)	Further thermal performance; U-value < 1.0 W/m².K	Passive house, cold-climate residential

The NCC NatHERS energy assessment typically requires Low-E or IGU glass to achieve compliance in climate zones 5-8. The glass spec is part of the window-and-door fabrication, not a separate item.

Where float glass is the right call

Standard windows in compliance zones (above 500 mm sill, not adjacent to doors): cheapest and most reliable for high-volume window orders
Picture-frame and decorative glazing: in non-impact applications
Substrate for value-added products: toughening, laminating, coating all start from float
IGU assemblies: the inner and outer panes of an insulated glass unit are typically annealed float (with Low-E coating on one face)

Where float glass is wrong

Any AS 1288 safety zone: shower screens, balustrades, low-level windows, doors. Mandatory safety glass.
High-impact areas: school sport halls, commercial public spaces. Toughened or laminated mandatory.
Skylights: laminated or toughened typically required for overhead glazing.
Cool-climate single-glazing: float alone doesn’t meet NCC NatHERS in zones 5-8; needs Low-E or IGU.
Bushfire-prone properties at BAL-19+: standard float typically replaced with toughened or laminated per AS 3959 detailing.

Quality grades

AS 4667:2018 sets quality requirements for cut-to-size and processed glass. The three quality grades:

Grade	What it allows
Q1 (premium)	Minimal optical defects; specifier residential, premium commercial
Q2 (standard)	The volume residential default; small defects acceptable per the standard
Q3 (utility)	Industrial / agricultural; larger defects acceptable

Most residential window glass is supplied as Q2 unless specified otherwise. Q1 carries a small price premium for premium frameless glazing and specifier-led work.

Common defects and on-site issues

Scratches at delivery: float glass is soft compared to toughened; scratches occur during handling. Inspect on receipt; reject scratched panes for visible applications.
Edge chip: chips reduce strength under wind pressure; the pane can break in service. Reject chipped panes.
Optical distortion (lensing, banding): a manufacturing defect that’s visible at certain angles. Q1 glass minimises this; Q3 may show it noticeably.
Glazing without setting blocks: float glass installed in a frame without setting blocks at the base concentrates load; spontaneous breakage is rare but possible.
Adjacent to thermal source (heat lamp, sun glare on dark interior surface): thermal stress fracture risk. Use toughened or pre-strengthened glass for thermal-stressed locations.
Wrong thickness for pane area: a 4 mm pane in a 2 m × 1.5 m window is below AS 1288 thickness requirement; failure under wind pressure. Read the AS 1288 selection table before ordering.

Cost (2026 indicative, ex-GST, supply only)

Item	Indicative cost
4 mm clear float, 600 × 900 mm	$25-45
6 mm clear float, 1200 × 1500 mm	$80-130
6 mm tinted float (grey, bronze, blue)	+20-40% over clear
Pyrolytic Low-E float (single-glazed)	+30-60% over clear
IGU (Low-E + argon + clear, 24 mm overall)	$180-280 per m² installed in window unit

Float glass is materially cheaper than toughened of the same size (often 40-60% less); lead time is days rather than the 2-4 weeks for toughened.

Standards and references

Standards Australia, AS 1288:2021 Glass in buildings: selection and installation. https://store.standards.org.au (verified 2026-05-13).
Standards Australia, AS 4667:2018 Quality requirements for cut-to-size and processed glass. https://store.standards.org.au (verified 2026-05-13).
Standards Australia, AS/NZS 4666:2012 Insulating glass units. https://store.standards.org.au (verified 2026-05-13).
Australian Building Codes Board, NCC 2022 Volume Two Part H4 and Part H6. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-two (verified 2026-05-13).