Glass (Construction Material)
Glazing used in windows and facades, chosen for safety, energy, and light.
Quick Answer
Architectural glass is glazing used in windows, storefronts, curtain walls, and railings. Common types include annealed, heat-strengthened, tempered, and laminated glass, usually assembled into insulating glass units with low-emissivity coatings. Specifications balance strength, safety, thermal performance (U-factor, solar heat gain), daylight, and acoustics.
The Full Picture
Glass in buildings is far more than clear panes. Architectural glazing is manufactured in several strength and safety categories. Annealed glass is the baseline and breaks into large sharp shards. Heat-strengthened glass is about twice as strong, and fully tempered glass is heat-treated to be several times stronger and to break into small, relatively blunt pieces. Laminated glass bonds layers with an interlayer, so broken pieces stay adhered, which supports safety, security, and acoustic goals.
Most exterior glazing is an insulating glass unit (IGU), two or more lites separated by a spacer with a sealed air or gas-filled cavity. Low-emissivity (low-e) coatings reduce heat transfer and control solar gain. The key performance values are U-factor (heat flow), solar heat gain coefficient (SHGC), and visible transmittance (VT), commonly rated and labeled through the National Fenestration Rating Council.
Specification involves matching glass to its use. Building codes require safety glazing in hazardous locations such as doors and areas near floors, and wind-borne debris or blast regions may require laminated or impact-rated products. Thickness and type are selected for wind load, thermal stress, and deflection under standards such as ASTM E1300. Fabrication options include fritting, tinting, coatings, and heat treatment, and some options increase lead time.
Glass is installed in aluminum or other framing systems, so the glass and framing are coordinated as a system. Pricing is typically by square foot of glazed area and varies widely with type, size, and coatings, so preconstruction teams verify the specified performance rather than assuming a standard product.
Real Examples
Common Misconceptions
People assume: Tempered glass cannot break.
Actually: Tempered glass is stronger, but it can break, for example from edge damage or impact, and it then fragments into small pieces. Laminated glass is the type designed to stay in place after breakage.
People assume: Thicker glass is always more energy efficient.
Actually: Thermal performance depends mainly on the IGU construction, coatings, gas fill, and framing, not on glass thickness alone.
Frequently Asked Questions
What is an insulating glass unit (IGU)?
An IGU is two or more glass lites separated by a spacer and sealed to form an air or gas-filled cavity, reducing heat transfer compared with a single pane.
What do U-factor and SHGC mean?
U-factor measures how readily heat flows through the glazing, where lower is better insulation. SHGC measures the fraction of solar radiation admitted as heat, where lower reduces solar heat gain.
When is laminated glass required?
Codes and project requirements call for it in certain cases such as overhead glazing, some guards, impact-rated or hurricane zones, and security or acoustic needs. Check the adopted code and design criteria.
What is low-e glass?
Glass with a thin low-emissivity coating that reflects infrared heat, reducing heat loss in winter and heat gain in summer while allowing visible light through.