Chapter 16 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, Polymer- modified 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

Metal Deck Welded to Structure 2 Rigid Insulation Mechanically Fastened

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 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

Parapet Parapet Flashing

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 – 12x36

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

Roofing Felt Asphalt 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 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