chapter 16 roofing
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
Chapter 16Roofing
Roofing
First line of defense against the weatherPrecipitation (Rain, snow)SunThermal Transmission
Subjected to extreme heat and cold
Surface can have wide temperature swings
Roof Groups
Steep Roofs
Low-Slope Roofs
Steep Roofs
Drain quicklyLess opportunity for gravity or wind to push/pull water
through the roofing material
Facilitate the use of shinglessmall, overlapping roofing unitsAdvantages:
Can be inexpensive, easy to handle & install, Accommodate thermal expansion/contraction & structural
movement Vents water vapor easily Visible - Aesthetics
Low Slope Roofs
Low-Slope RoofsAdvantagesCan cover a “large” horizontal surface (vs steep)Simpler geometry, often less expensiveRoof can have other functions - patio, decks, parking, ...
DisadvantagesWater Drains SlowlySlight Structural Movements Tear the MembraneWater 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 requirementsSupport Roof LoadingResist UpliftSloped for Drainage Expansion & Contraction - Roof & StructureSmooth, Clean SurfaceDry Prior to Membrane Placement
Thermal Insulation
Resist Heat Transfer
Location / PlacementBelow the DeckBetween the Deck & MembraneAbove 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 VaporLocation / PlacementGenerally Below the Insulation
Material - hot mopped felts most common
Insulation VentilationRoof 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
weldingPolyvinyl Chloride (PVC) – widely used,
Polymer-modified bitumens, PVC alloys, etc.
Thermosetting Can not be softened - must be joined by adhesives
or pressure sensitive tapesEPDM (Ethylene propylene diene monomer),
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
Metal DeckWelded to Structure
2” Rigid InsulationMechanically Fastened
Insulation Fastener
Insulation Fastener - penetrates through the insulation to the metal deck
Roof Membrane Rolls
Lap Markings
FastenerLocations
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 MaterialStone aggregatePrecast concrete blocks or Pavers
PurposeHold down membraneProtect membrane from ultraviolet lightProtect 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 CategoriesThatchShinglesArchitectural sheet metal
Insulation & vapor retarderTypically 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”
MaterialsWood (shingles & shakes)AsphaltSlatesClay TilesConcrete 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 AsphaltShingleProfiles & 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
Roofing FeltAsphalt Shingles - Packaged
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 resistanceClass A: effective against severe fire 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