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Chapter 17 Glass and Glazing

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Chapter 17 Glass and Glazing. Glass. Benefits of Using Glass Allows entry of natural light Provide “views” of exterior environment Entry of sunlight provides warmth Disadvantages and/or Design Considerations Limits occupant’s privacy Lower resistance to thermal transmission

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  • Benefits of Using Glass
    • Allows entry of natural light
    • Provide “views” of exterior environment
    • Entry of sunlight provides warmth
  • Disadvantages and/or Design Considerations
    • Limits occupant’s privacy
    • Lower resistance to thermal transmission
      • heat in the summer &
      • Cold in the winter
    • Initial & operating costs
glass history
Glass History

Material used for Centuries

  • Early Processes (10th Century)
    • Crown Glass
      • Heated glass blown into sphere
      • Reheated & spun on “punty”(rod)
      • Sphere becomes a “disk”
      • Cooled & cut into pieces
    • Cylinder glass
      • Heated glass blown into sphere
      • Swung like a pendulum
      • Elongated into a cylinder
      • Ends cut off, split lengthwise
      • Reheated, opened, flattened into rectangular sheet
      • Cut into pieces
    • Neither had high “optical” quality
glass history cont
Glass History (cont.)
  • Plate Glass
    • Introduced in the 17th Century
    • Process
      • Molten glass cast into frames
      • Spread into sheets by rollers
      • Cooled
      • Each side ground / polished
    • Larger sheets of High optical quality
    • Costly (until process was mechanized)
glass history cont1
Glass History (cont.)
  • Drawn Glass
    • Replaced cylinder glass, early 20th century
    • Flat sheets of glass drawn directly from a molten glass container
    • Production Process
      • Continuous production line - highly mechanized
        • Drawn glass
        • Ground & Polished (plate)
        • To finished sheets of glass
glass history cont2
Glass History (cont.)
  • Float Glass
    • Process invented in 1959 in England (produced in US, 1963)
      • Has become a worldwide standard
      • Largely replaced drawn & plate glass
    • Production Process (Glass “floated” across a bath of molten tin)
ribbon of float glass
Ribbon of Float Glass
  • Process Benefits
  • Surfaces parallel
  • High Optical Quality
    • (Comparable to Plate)
  • Brilliant Surface Finish
  • Economical
  • Virtually all flat glass produced
  • Glazing - “...installation of a transparent material (usually glass) into an opening”
    • I.E. “Glass & Glazing”
  • Glazier
    • A glass installer
  • Lites (lights)
    • Individual pieces of glass
glass as a material
Glass as a Material
  • Major ingredient - Sand (silicon dioxide)
  • Strength
    • Individual fibers stronger than steel, but less stiff
    • In larger sheets - microscopic imperfections inherent with manufacturing process significantly reduce its strength
    • Cracks propagate from these imperfections near the point of maximum tension
    • Types of Breakage
      • Thermal Stress Breaks
      • Mechanical Stress Breaks
glass thicknesses
Glass Thicknesses
  • Range of Thicknesses
    • 3/32” Single strength
    • 1/8” Double strength
    • Up to 1”+
  • Thickness Required is Determined by:
    • Size of Glass Lites (span)
    • Maximum Design (Wind) Loading
    • Acceptable Breakage Rate (most always some breakage)
wind testing common on tall buildings purpose establish expected loads
Wind TestingCommon on tall Buildings - Purpose: Establish expected loads

Mockup for a 24 Story Condo

tempered glass
Tempered Glass
  • Ordinary Glass - Annealed
    • glass cooled slowly under controlled conditions to avoid internal stresses
  • Tempered Glass
    • Annealed glass that is:
      • Reheated
      • Surfaces cooled rapidly, core cooled more slowly
      • Induces permanent compressive stresses in edges & faces and tensile stresses in the core
      • Result:
        • 4 times as strong in bending
        • More resistant to thermal stress & impact
tempered glass1
Tempered Glass
  • When Tempered Glass Breaks:
    • The sudden release of the internal stresses:
      • Produces small square edged particles (as opposed to sharp, jagged pieces)
  • Strength & breakage characteristics make it well suited for:
    • Exterior Doors
    • Floor to Ceiling Sheets of Glass
    • All-Glass Doors, Glass walls (ex; handball courts), basketball backboards
  • Disadvantages
    • More Costly
    • Process may cause noticeable distortions
    • Cutting & Drilling must be prior to tempering
heat strengthened glass
Heat-Strengthened Glass
  • Substitute for Tempered Glass
    • Lower Cost, but
    • Less of the desirable qualities of tempered
      • Lower strength
      • Less desirable breakage characteristics
  • Process Similar, however
    • Lower induced stresses
    • Less strength (only twice annealed)
    • Breakage characteristics more similar to annealed
laminated glass
Laminated Glass
  • Sandwiching
    • Transparent interlayer (PVB)
    • Between layers of glass (can be multiple layers)
    • Bonded under heat & pressure
  • PVB - Polyvinyl Butyral
    • Soft interlayer
    • Can be clear, colored, and/or patterned
    • Improves resistance to sound transmission
    • Upon breakage - PVB holds pieces of glass together
  • Uses?
    • Skylights (overhead glazing)
    • Reduce noise (hospitals, classrooms, etc.)
    • Security glass (typically has multiple layers)




Hurricane Resistant Glass

Large Missile Impact Test

Laminated and Tempered

fire rated glass
Fire Rated Glass
  • Required for:
    • Fire rated doors
    • Rated Window and wall assemblies
  • Glass Types
    • Specially Tempered Glass (rated for 20 minutes)
    • Wired Glass (mesh of wire in glass, rated for 45min.)
      • most common, but
      • changes the appearance of the opening
    • Optical Quality Ceramics (20min. to 3hr)
spandrel glass
Spandrel Glass
  • Interior face
    • Ceramic based paints w/ pigmented glass particles (frits) applied
    • Heated / Tempered to form a ceramic coating
    • Opaque Lite
    • Match or contrast other glass
    • Often tempered - resist thermal stresses behind light
  • Purpose
    • Conceal structure behind glass / curtainwall
Spandrel Glass

(view from the inside)

Spandrel Glass

(view from the outside)

tinted reflective glass
Tinted & Reflective Glass
  • Why tint or apply a reflective coating to glass?
    • Reduce glare from sunlight
    • Reduce solar heat gain
    • Architectural look - Aesthetics
clear float glass
Clear Float Glass


85% +/-



Reflected Sunlight

Absorbed & Reradiated as Heat



tinted glass
Tinted Glass


14% to 75%


  • Result:
    • Lower Cooling Costs
    • Less “sunlight”
      • Glare for people
      • Fading FF&E





tinted glass1
Tinted Glass
  • Process
    • Chemical elements added to the molten glass
    • Colors available
      • Grays, bronzes, blues, greens, golds, etc.
reflective glass
Reflective Glass
  • Thin films of metal or metal oxide placed on the surface of the glass
  • Film purpose:
    • Reflect sunlight
      • Reduce solar heat gain
    • Changes Appearance
      • Colored Mirror effect
  • Can be placed on either face,
    • However, often on the inside face




shading coefficient
Shading Coefficient
  • “Ration of total solar heat gain through a particular glass compared to heat gain through double-strength clear glass.”
  • Shading Coefficient = Heat gain of a Glass type

Heat gain thru Clear (double-strength)

  • Tinted glass range: .5 to .8
  • Reflective glass range .3 to .7
visible transmittance
Visible Transmittance
  • “Measures the transparency of glass to visible light (rather than solar heat gain)
  • Ranges:
    • Clear Glass .9
    • Tinted & Reflective < .9
glazing luminous efficacy k e
Glazing Luminous Efficacy (Ke)
  • Ke = Visible Transmittance

Shading Coefficient

  • High Ke
    • High amount of solar heat blocked while
    • Considerable amount of sunlight allowed to enter
    • Green & blue glass
  • Low Ke
    • Similar amounts of solar heat & sunlight blocked
    • Darker interior (less light)
    • Bronze, gold, & grays
glass thermal transmission
Glass & Thermal Transmission




Single Pane




Thermal Transmission

1/5 of Glass

1/20 of Glass

Disadvantage of Glass: Higher Initial & Operating Costs, Reduced Comfort

insulating glass
Insulating Glass
  • Two or more sheets of glass separated by an air space
    • Double Glazing: Two (2) sheets
    • Triple Glazing: Three (3) sheets (somewhat uncommon)
  • Primary purpose of additional sheets of glass
    • Improve insulating value - reduce thermal transmission
    • Two (2) sheets - cuts heat loss in half (1/3 for 3 sheets)
  • Increases initial cost but:
    • Reduces operating costs
    • Increases comfort
    • Provides additional architectural options
insulating glass1
Insulating Glass



  • Spacer (Spline)
    • Separates the glass
    • Often Metallic
  • Air Space
    • Dry Air or
    • Inert Gas (such as Argon)
  • Sealant
    • “Seals” Unit
    • Prevent air escape &
    • moisture penetration
  • Glass
    • Clear, reflective and/or tinted




low emissivity glass low e glass
Low-Emissivity GlassLow-E Glass

Insulated Glass

  • Improves thermal performance
    • Ultra-thin, transparent, metallic coating
    • Generally placed on:
      • The #2 or #3 position in insulating glass or
      • The #4 position in laminated glass
    • Reflects selected wavelengths of light & heat radiation
      • Allows entry of most short-wave (sunlight)
      • Reflects most longer-wave infrared radiation from objects and humans inside the building
    • Result:
      • Reduced heating & cooling load, increased comfort






thermal performance data obtained from ppg glass
Thermal Performance Data Obtained from PPG Glass

13% Improvement



6% Improvement

Add “special” spacer

33% Improvement

Add Low-E Glass

Clear, insulated, alum. spacer, air filled

glass with changing properties
Glass with Changing Properties
  • Thermochromic glass (darker when warmed by the sun)
  • Photochromic (darker when exposed to bright light)
  • Electrochromic (changes transparency with electricity)
  • Photovoltaic (generates electricity from sunlight)
Self-Cleaning Glass
    • Proprietary product w/ coating of titanium oxide
    • Catalyst allowing sunlight to turn organic dirty into carbon dioxide and water
  • Plastic Glazing Sheet
    • Materials – acrylic & polycarbonate
    • More expensive, higher coefficients of thermal expansion
glazing small lights
Glazing - Small Lights
  • Design Considerations
    • Low stresses from wind loading
    • Low stresses from thermal expansion / contraction

Glazier’s points &




Snap-in Glazing Beads &

Synthetic Rubber Gaskets

glazing large lites
Glazing - Large Lites
  • Design Considerations
    • Greater spans, Larger wind loads
    • Greater stresses from thermal expansion / contraction
    • Minor Frame irregularities can induce stresses
  • Design Objectives
    • Effectively support glass weight (w/o inducing abnormal stresses)
    • Support glass against wind pressure (both positive & negative)
    • Isolate glass from from the supporting frame & building structure
    • Allow for independent expansion/contraction (glass & supports)
    • Separate glass from support materials that could induce stress or cause abrasion
glass support isolation from frame
Glass Support &Isolation from Frame
  • Setting Blocks
    • Synthetic Rubber
    • Set @ the bottom edge
    • Often two/lite @ quarter pts.
  • Centering Shims
    • Synthetic Rubber
    • Center Lite
    • Isolate Lit from the Frame


  • Support against Wind Pressure
    • Bite
      • Too little - pop out
      • Too much - stress w/
      • glass deflection
    • Supporting Mullion
      • Support Glass
      • Transmit loads to structure
    • “Seals” the Glass (1st line of defense)
    • “Isolates” glass (from abrasion)
    • Allows for Thermal Expansion/Contraction
    • Accommodates Structure/Support deflection
anchorage of glass to mullion s
Anchorage of Glass to Mullion(s)

‘Dry’ Glazed Lite (using compression)

Insulated Glass


Glass being installed

Finished Installation

(Snap on Covers applied over the retainer strips)

Structural Silicone Flush Glazing

Mullions on

the “inside” of the


Glass adhered

by Silicone

Sealant or


Butt-Joint Glazing
  • Head & Sill with
  • conventional frames
  • Vertical Mullions
  • eliminated
  • Vertical joints - caulked
Truss-like Mullions

with ‘architectural qualities’ to

support wind loading on a tall entrance



Mullion Colors

Aluminum & Glass L.C.

Tempered & Laminated Glass

Glass support & anchorage

Suspended Glazing System









glass design
Glass & Design
  • Methods to compensate for its poor thermal properties
    • Double & triple glazing
    • Low E coatings
    • Low conductivity gas fills
    • Tinting, reflective coatings
    • Curtains, shutters
    • Window sizing & orientation on the building
    • Shading or overhangs
glass the building codes
Glass & the Building Codes

Codes concerned with:

  • Structural Adequacy
    • wind & impact loads
  • Providing natural light in habitable rooms
    • may require a certain glass area as a % of floor area
  • Safety concerns with breakage
    • skylights, overhead glazing, in or near doors, “clear” sheets of glass that could be mistaken for an opening
    • Use of laminated, tempered, etc.
  • Prevention of fire
    • maximum glazed area, wire glass
  • Energy consumption
    • may require double glazing, storm windows, limit the maximum % of glazed area