Glass

Summary

Glass in buildings is mostly soda-lime-silicate float glass, about 70 to 74 percent silica, supplied as annealed, heat-strengthened, tempered, and laminated flat glass. Commercial glass breaks at flaw-limited tensile stresses of 2,000 to 25,000 psi, so thickness, heat treatment, and lamination must be matched to load and safety needs.

Cols

Image

Float glass: flat glass formed by floating molten glass on a tin bath
Soda-lime glass: about 90 percent of modern manufactured glass
Annealed: slowly cooled in a lehr to relieve stress
Cullet: recycled broken glass added to the batch
Plate glass: older cast, ground, and polished flat glass
Crown / cylinder glass: older window glass made by spinning discs or blowing cylinders
Low-iron: float glass with reduced iron for clarity

History and demand

Invention

At least 3600 BC: glassmaking in Mesopotamia, Egypt, or Syria; sustained production about 1600 BC in Mesopotamia and 1500 BC in Egypt
13th century: Murano cristallo, used extensively for windows among other products
1953 to 1957: Alastair Pilkington and Kenneth Bickerstaff developed float glass at Cowley Hill Works, St Helens; full-scale profitable sales began in 1960

First uses in construction

Window glass was made as crown glass until the 16th century, as cylinder glass in the early 19th century, and as costly polished plate; continuous grinding lines appeared in the early 1920s
1960s: float glass became widespread

Sourcing

Flat glass 2024: China made about 1.2 billion m2, 23 percent of about 5.3 billion m2 world output; the United States about 451 million m2 and India about 386 million m2 (IndexBox)

Demand trend

Float glass is the most widely produced form of glass

Composition and production

Raw materials

Sand, soda ash, dolomite, limestone, and salt cake, plus cullet
Soda-lime-silicate glasses are over 75 percent of manufactured glass, with 70 to 74 percent silica by weight

Manufacturing process

Batch melted with cullet at about 1,500°C (2,730°F), stabilized at about 1,200°C (2,190°F)
Molten glass pours onto a tin bath, cooling from about 1,100°C to about 600°C (2,010 to 1,110°F) as it spreads into a flat ribbon
Annealed in a lehr about 100 m long, then cut

Product forms

Flat glass in varied thickness (set by flow and roller speed), later heat-treated, laminated, or coated

Properties

Physical

Density (all glasses): 2.2 to 7.2 g/cm³

Mechanical

Tensile strength: theoretical for flawless glass 14 to 35 GPa; commercial glass 14 to 175 MPa (about 2,000 to 25,400 psi) because of flaws

Thermal and moisture

Coefficient of thermal expansion (soda-lime): about 9 × 10⁻⁶/°C, or 5.0 × 10⁻⁶ in./in./°F; high expansion and poor heat resistance, against 3.25 × 10⁻⁶/°C for borosilicate

Standards

Material specifications

ASTM E1300: load resistance of glass in buildings
ANSI Z97.1: safety glazing
16 CFR 1201 (CPSC): architectural glazing

Uses in buildings

Building elements

Fixed Windows, Casement Windows, Awning Windows, Double-Hung Windows, Horizontal Sliding Windows, Aluminum Windows, Vinyl Windows, Fiberglass Windows, Wood and Clad Wood Windows: insulating glass units
Curtain Wall Systems, Aluminum Storefront Doors, Sliding and Folding Glass Wall Systems: glazing infill
Frameless Glass Doors, Automatic and Revolving Doors: tempered glass leaves and glazed panels
Skylights and Roof Windows: skylight glazing
Overhead Sectional Doors, Fiberglass Entry Doors, Stile and Rail Wood Doors, Pocket and Sliding Interior Doors: glazed sections, door lites, and glass sliding leaves
Rooftop Solar PV: module cover glass
Terrazzo, Wall Sconces: recycled glass aggregate, and shades
Guards and Railings: laminated glass infill

Pros and cons

Pros

Transparent and easily formed
Float process gives flat, even sheets
Recycled cullet is part of the batch

Cons

Brittle; commercial tensile strength limited by flaws to 14 to 175 MPa
High thermal expansion and poor heat resistance

Design considerations

Movement

Expansion about 0.06 in. per 10 ft for a 100°F swing (calculated from 5.0 × 10⁻⁶ in./in./°F)

Finishes and treatments

Coated and heat-treated glass: processed beyond the unprocessed flat glass in industry EPD scope

Sustainability

Embodied carbon

NGA industry-average flat glass EPD (2019, United States, unprocessed clear, tinted, and low-iron): 1,430 kg CO2e per ton
Guardian North America unprocessed flat glass EPD: about 1,102 kg CO2e per ton (A1 to A3)
Coated, heat-treated, or otherwise processed glass is outside both declarations

Manufacturing and cost

Main manufacturers and suppliers

Trade association: National Glass Association.

Sources

Wikipedia: Glass, https://en.wikipedia.org/wiki/Glass
Wikipedia: Float glass, https://en.wikipedia.org/wiki/Float_glass
Glass Online: Guardian Glass publishes new EPD for its North America glass products, https://www.glassonline.com/guardian-glass-publishes-new-epd-for-its-north-america-glass-products/
National Glass Association: flat glass global warming one-pager, https://www.glass.org/sites/default/files/2021-01/NGA Flat Glass Global Warming One Pager Advocacy One-Pager.pdf
UpCodes: 2024 IBC Chapter 24 glass and glazing, https://up.codes/viewer/department-of-defense/ibc-2024/chapter/24/glass-and-glazing
Wikimedia Commons: Interior of the Tokyo International Forum Glass Building, Japan.jpg, photo by Basile Morin (CC BY-SA 4.0), https://commons.wikimedia.org/wiki/File:Interior_of_the_Tokyo_International_Forum_Glass_Building,_Japan.jpg
IndexBox: flat glass world market overview 2024, https://www.indexbox.io/blog/flat-glass-world-market-overview-2024-8/