chapter 16 roofing. first line of defense against the weather precipitation (rain, snow) sun thermal...

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