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 (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

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 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