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
 heat in the summer &
 Cold in the winter
Initial & operating costs
Glass History
Material used for Centuries
Early Processes (10th Century)
 Crown Glass
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Heated glass blown into sphere
Reheated & spun on “punty”(rod)
Sphere becomes a “disk”
Cooled & cut into pieces
 Cylinder glass
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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.)
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 (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
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Drawn glass
Ground & Polished (plate)
To finished sheets of glass
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
Process Benefits
•Surfaces parallel
•High Optical Quality
(Comparable to Plate)
•Brilliant Surface Finish
•Economical
•Virtually all flat glass produced
Terminology
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
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
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
Mockup for a 24 Story Condo
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:
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
4 times as strong in bending
More resistant to thermal stress & impact
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
Uses of Tempered 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
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)
Glass
PVB
Layer
Skylight @ the Bellagio Hotel
Hurricane Resistant Glass
Large Missile Impact Test
Laminated and Tempered
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)
Wire 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)
Spandrel 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
Absorbed & Reradiated as Heat
Outside
85% +/sunlight
enters
Inside
Tinted Glass
Reradiated
Outside
Reradiated
Inside
Result:
•Lower Cooling Costs
•Less “sunlight”
Glare for people
Fading FF&E
Tinted Glass
Process
Chemical elements added to the molten glass
Colors available
 Grays, bronzes, blues, greens, golds, etc.
Clear (untinted) Glass
Lightly tinted glass
Lightly tinted glass
Tinted glass
Reflective Glass
Thin films of metal or metal oxide placed on the
surface of the glass
Film purpose:
Glass
Reflect sunlight
 Reduce solar heat gain
Changes Appearance
 Colored Mirror effect
Can be placed on either face,
However, often on the inside face
Reflective
Film
Reflective Glass
Reflective Glass
Reflective Glass
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
“Measures the transparency of glass to
visible light (rather than solar heat gain)
Ranges:
Clear Glass
Tinted & Reflective
.9
< .9
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
Single Pane
Glass
1”
Polystyrene
“Well”
Insulated
Wall
Thermal Transmission
1/5 of Glass
1/20 of Glass
Disadvantage of Glass: Higher Initial & Operating Costs, Reduced Comfort
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 Glass
Spacer (Spline)
•Separates the glass
•Often Metallic
Air
Space
Glass
Air Space
•Dry Air or
•Inert Gas (such as Argon)
Sealant
Spacer
•“Seals” Unit
•Prevent air escape &
moisture penetration
Glass
•Clear, reflective and/or tinted
Sealant
Insulated Glass (tinted)
Insulated Glass (tinted)
Metal Spline
Low-Emissivity Glass
Low-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
inside
1
2
3
4
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
Add
Argon
13% Improvement
Add “special” spacer
Add Low-E Glass
6% Improvement
33% Improvement
Clear, insulated, alum. spacer, air filled
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
Design Considerations
Low stresses from wind loading
Low stresses from thermal expansion / contraction
Glazier’s points &
Putty
Wood
Stop
Snap-in Glazing Beads &
Synthetic Rubber Gaskets
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
Setting Blocks
•Synthetic Rubber
•Set @ the bottom edge
•Often two/lite @ quarter pts.
Centering Shims
•Synthetic Rubber
•Center Lite
•Isolate Lit from the Frame
Mullion
Bite
Support against Wind Pressure
•Bite
•Too little - pop out
•Too much - stress w/
glass deflection
•Supporting Mullion
•Support Glass
•Transmit loads to structure
Gaskets
•“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)
‘Dry’ Glazed Lite (using compression)
Mullions being anchored to the structure
Insulated Glass
Gaskets
Glass being installed
Retainer (compression) strips installed
Finished Installation
(Snap on Covers applied over the retainer strips)
Lock-Strip Gasket
Structural Silicone Flush Glazing
Mullions on
the “inside” of the
Glass
Glass adhered
by Silicone
Sealant or
Retainer
Structural Silicone Flush Glazing
Structural Silicone Flush Glazing
Butt-Joint Glazing
•Head & Sill with
conventional frames
•Vertical Mullions
eliminated
•Vertical joints - caulked
Butt-Joint Glazing
Truss-like Mullions
with ‘architectural qualities’ to
support wind loading on a tall entrance
Weeps / “Drainage” System
Sampling
of
Mullion Colors
Aluminum & Glass L.C.
Tempered & Laminated Glass
Glass support & anchorage
Suspended Glazing System
Structural
Glazing
System
(exterior)
Structural
Glazing
System
(interior)
Glass Mullion System
tempered glass
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
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