Arch 330 Thermal & Moisture Protection — Lecture 21: Roofing Systems

Steep Slope • Thermal expansion / contraction minimized • Movement in structure is minimized ­ by the ability of small units to move with ­ respect to one another. • Water vapor vents from the interior through the loose joints in the roofing material. Item Spotted: A combination of a flat and gamble roof Observations: This building has a very interesting skyline because of the combination roof. However if one was to look closely at the picture, one con see puddles of standing water. Location: Smith Gym, WSU Campus Name: Kallen Hawthorne ID# 10596914 LOW SLOPE ROOF (not FLAT) < 3:12 pitch • Min Slope • 1/8” per 1’­0” or 1:100 • 1/4” per 1’­0” or 1:50 Low < 3:12 pitch 1/4 Roof Slope • Slope Roof to direct water towards drainage points ­ counter­acting structural deflection. • Depending on size of deck expansion joints should be provided to ­ control expansion and contraction and ­ satisfy requirements of membrane. • Membrane should be laid on flat surface. FLAT ROOF ­ COMPONENTS • DECK • THERMAL INSULATION • VAPOR RETARDER • MEMBRANE • FLASHINGS • DRAINAGE COMPONENTS Deck:Types of structural deck used for low slope roof • Plywood over wood joists • Solid wood decking over heavy timber framing • Corrugated steel decking • Panels of wood fiber bonded together with portland cement • Poured gypsum over insulating formboard • Sitecast concrete and precast concrete Insulating Deck Boards – wood/glass fibers Truss Tee Purlins + slab of gypsum/lt wt conc Thermal Insulation • Below the Deck • Between Deck + Membrane • Above the Membrane Thermal Insulation: Below the Deck • Leaves the deck and membrane exposed to full range of temperature. • Batt insulation of glass fiber or mineral fiber between wood joists ­ or on top of a suspended ceiling assembly. • Vapor retarder below insulation (Vapor retarder on warm side of insulation) Insulation: Between Deck and Membrane • Rigid panels of insulation, light weight concrete. • Protects deck from temperature extremes. • Membrane subjected to extreme temperature variations. • Moisture trapped in insulation can damage insulation and deck. • Place vapor retarded on inside of insulation and vent insulation to release moisture. Insulation: Above the Membrane • Membrane protected ­ extremes of temperature. • Membrane on warm side of insulation ­ immune to vapor blistering. • Insulation must be a material which is not effected by wet and will not disintegrate ­ extruded polystyrene board • Insulation board adhered in bed of hot asphalt or laid loose. • Layer of ballast laid over insulation. Insulation: Above the Membrane • Ballast ­ crushed stone ­ thin concrete layer factory laminated to upper surface of insulation board ­ interlocking concrete blocks. • Membrane ages little protected from sunlight and temperature extremes ­ despite presence of moisture. • Rigid insulation ­ mechanical fix to deck preferable. Insulation above the Membrane: Other names for this system • Inverted roof • Upside down roof • Protected membrane roof, +­ 20years old Vapor Retarder • 2 sheets asphalt saturated roofing felt • In cold climate on warm side of insulation. • In hot humid climate/with air conditioning ­ on outer side of insulation** Membrane • Built up roof membrane • Single­ply roof membrane • Fluid­applied roof membrane Built­up membrane • 2­4 Layers/ plies of felt asphalt impregnated, bedded in bitumen felt: cellulose fibers/glass fibers +asphalt • Felt laminated in overlapping layers • Layer of aggregate (crushed stone) Built-Up Membrane • Bitumen ­ asphalt derived • For low pitch roofs ­ coal tar bitumen or coal­tar pitch used­ ­ greater resistance to standing water • Asphalt and coal tar are applied hot • Aggregate • Insulation • Felt • Conc. Deck • Aggregate • Felt • Insulation x 2 • Metal Deck • 4 ply felt + hot asphalt Single Ply Roof membrane • Single layer • More elastic ­ less cracking/tearing • Fixing: adhesives, ballast, concealed fasteners, mechanical fasteners. • Protective coating Single Ply Roof Membrane • EPDM , synthetic rubber (ethylene propylene diene monomer) • NEOPRENE (polychloroprene) synthetic rubber compound • PVC (polyvinyl chloride) vinyl ­ thermoplastic compound Single-Ply Membrane Aluminum Faced Single-Ply Membrane Fluid Applied Membrane • domes, vaults, complex shapes • roller or spray gun, applied • several coats ­ rubbery membrane. Built-Up + Single Ply Ballast • loose stone aggregate • precast concrete blocks. • Ballast holds the membrane in place against wind uplift • Protects membrane from ultraviolet light and physical wear. • Increase the fire resistance of the roof covering. Traffic Decks-walks, terraces, parking onpaving lowslabs slope roof (a) Heavy – square or stones –open joints on blocks of plastic or conc on roof membrane (b) Open Jointed Paving Blocks on A drainage layer of gravel or porous concrete leveled over the membrane • • Water falls through the joints and is drained away by the membrane below Membrane is not pierced. Structural Standing Seam Metal Roofing for Low Slope Roofs: • Proprietary systems of standing seam metal roofing • Used as low slope roofs ­ 1/4" in 12 "(1:48).