Presentation on theme: "Chapter 16 Roofing. First line of defense against the weather Precipitation (Rain, snow) Sun Thermal Transmission Subjected to extreme heat and cold Surface."— Presentation transcript:
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
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
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
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.
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
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
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
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