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       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.)

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  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)

Process Benefits

•Surfaces parallel •High Optical Quality (Comparable to Plate) •Brilliant Surface Finish •Economical •Virtually all flat glass produced Ribbon of Float Glass

Terminology

Glazing opening” “...installation of a transparent material (usually glass) into an  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:  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 Inside 85% +/ sunlight enters

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:  Reflect sunlight  Reduce solar heat gain  Changes Appearance  Colored Mirror effect Can be placed on either face,  However, often on the inside face Glass 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: Reflective glass range .5 to .8

.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 (K

e

) K

e

= Visible Transmittance Shading Coefficient High K

e  High amount of solar heat blocked while  Considerable amount of sunlight allowed to enter  Green & blue glass

Low K

e  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 •Dry Air or •Inert Gas (such as Argon) Sealant •“Seals” Unit •Prevent air escape & moisture penetration Glass •Clear, reflective and/or tinted

Air Space

Glass Spacer 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 #4 position in laminated glass Reflects

selected

1 2 3

wavelengths of light & heat radiation

4

 T he #2 or #3 position in insulating glass or Allows entry of most short-wave (sunlight)  Reflects most longer-wave infrared radiation from objects and humans inside the building

inside

 Result:  Reduced heating & cooling load, increased comfort

Thermal Performance Data Obtained from PPG Glass Add Argon

13% Improvement

Add “special” spacer

6% Improvement

Add Low-E Glass

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 Suspended Glazing System Glass support & anchorage

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