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Chapter 16
Roofing
Roofing
First line of defense against the weather
Precipitation (Rain, snow)
Sun
Thermal Transmission
Subjected to extreme heat and cold
Surface can have wide temperature swings
Roof Groups
Steep Roofs
Low-Slope Roofs
Steep Roofs
Drain quickly
Less opportunity for gravity or wind to push/pull water
through the roofing material
Facilitate the use of shingles
small, overlapping roofing units
Advantages:
 Can be inexpensive, easy to handle & install,
 Accommodate thermal expansion/contraction & structural
movement
 Vents water vapor easily
 Visible - Aesthetics
Low Slope Roofs
Low-Slope Roofs
Advantages
Can cover a “large” horizontal surface (vs steep)
Simpler geometry, often less expensive
Roof can have other functions - patio, decks, parking, ...
Disadvantages
Water Drains Slowly
Slight Structural Movements Tear the Membrane
Water Vapor Pressure Can Blister & Rupture the Membrane
Low-Slope Roof Components
Structural Support - Deck
Thermal Insulation
Vapor Retarder
Roof Membrane
Roof Ballast
Drainage
Flashing
Roof Deck
Materials (Plywood, OSB, Steel, Concrete)
Performance requirements
Support Roof Loading
Resist Uplift
Sloped for Drainage
Expansion & Contraction - Roof & Structure
Smooth, Clean Surface
Dry Prior to Membrane Placement
Thermal Insulation
Resist Heat Transfer
Location / Placement
Below the Deck
Between the Deck & Membrane
Above the Membrane
Rigid Insulation Attachment (adhered or mechanically
attached)
‘Rigid’ roof insulation being placed over metal decking
(mechanically fastened to decking)
Vapor Retarder
Purpose - Prevent transmission of Water Vapor
Location / Placement
Generally Below the Insulation
Material - hot mopped felts most common
Insulation Ventilation
Roof Vent
Roof Membranes
Three Categories
Built-up Roof (BUR) Membrane
Single-Ply Roof Membrane
Fluid Applied Roof Membrane
Built-up Roof Membrane
“Multiple plies of asphalt-impregnated felt
bedded in bitumen”
Application:
Felts laid in Hot Asphalt (or coal tar)
Overlapping Layers
Forms a “laminated” membrane
typically 2-4 plies thick
Asphalt Felts
Felts being ‘Hot-Mopped’
Kettle for heating the bitumen
and pumping it to the roof
Single-Ply Roof Membrane
“Sheet materials that are applied to the roof in
a single layer”
Attached to the Roof:
Adhesives
Ballast Weight
Concealed fasteners
Single Ply Materials
Thermoplastics
May be softened and joined by heat or solvent
welding
Polyvinyl Chloride (PVC) – widely used, Polymermodified bitumens, PVC alloys, etc.
Thermosetting
Can not be softened - must be joined by adhesives
or pressure sensitive tapes
EPDM (the most widely used), Neoprene, CPE,
etc.
The following series of photos are from the
roofing operations of a 47,000sf single story
retail facility.
The roof system:
 Uses rigid insulation over metal decking with a:
Thermoplastic Membrane where the
Sheets are mechanically fastened to the structure
and the seams welded
2” Rigid Insulation
Mechanically Fastened
Metal Deck
Welded to Structure
Insulation
Fastener
Insulation Fastener - penetrates through the insulation to the metal deck
Roof Membrane Rolls
Lap
Markings
Fastener
Locations
Membrane being rolled out
Rolled out & leading edge attached
Membrane Mechanical Fastener
(penetrates the insulation and anchors to the metal deck)
Membrane
Lap
Welding Machine
(welds the seams)
Lap Welded
Membrane Flashing @ Curbs
Fluid-Applied Membranes
“Membranes applied with a roller or spray
gun and cure to form a rubbery membrane”
Uses
“Complex shapes that are difficult to
roof by conventional means”
Examples: Domes and shells
Ballast & Traffic Decks
Ballast Material
Stone aggregate
Precast concrete blocks or Pavers
Purpose
Hold down membrane
Protect membrane from ultraviolet light
Protect membrane from physical wear
Traffic Decks – installed over membranes for
walks, terraces, drives, etc.
Roof Flashing - Roof Edge
Edge Flashing
Expansion Joint - Building
Building/Roof Expansion Joint
Area Divider
Area Divider
Parapet
Parapet Flashing
Roof Drain
Roof Drain
Roof Penetration
Penetration - Vent
Steep Roofs
Roofs with a pitch of 3:12 (25%) or greater
Three General Categories
Thatch
Shingles
Architectural sheet metal
Insulation & vapor retarder
Typically installed below the roof decking
Decking – typically plywood or OSB
Shingles
“applied to the roof in small units and in
overlapping layers with staggered vertical
joints”
Materials
Wood (shingles & shakes)
Asphalt
Slates
Clay Tiles
Concrete Tiles
Cedar Shakes (split rather than sawn)
•Natural decay resistant wood
•Moderately expensive
•Fire Resistance low unless treated
Asphalt Shingles
•Die-cut from sheets of asphalt-impregnated
felt faced with mineral granules
•Typical size – 12”x36”
Different
Asphalt
Shingle
Profiles
& Colors
Slate:
•Fire-resistant
•High initial cost, but long life
Slate Roofing & Copper Flashing
Slate w/ Predrilled Holes
Clay Tiles
Concrete Tile
Asphalt Felt – typically adhered to the deck prior to the installation of the shingles
Asphalt Shingles - Packaged
Roofing Felt
Laid from the Eave up
Ridge Treatment &
Valley Flashing
Architectural Sheet Metal Roofing
•Materials – typically thin sheets of aluminum or galvanized steel
•Coatings – typically a polymeric available in various colors
•Seams – raised interlocking edge seams
•Fasteners – concealed or exposed fasteners with rubber washers
Lead Coated Copper
Roofing & the Building codes
Classified based upon Flame Spread resistance
Class A: effective against severe fie exposure
 Slate, concrete & clay tiles, asphalt shingles with glass
felts, & most built-up and single ply
Class B: effective against moderate fire exposure
 Many of the built-up & single ply, metal roofs, asphalt
shingles based upon organic felts
Class C: effective against light fire exposure
 Fire retardant wood shingles & shakes