Featuring Plywood in Buildings - Engineered Wood Products ...

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Lightweight Roofing SystemT&G structural plywood in combination with shingles or overlayed waterproof membranes canprovide a safe, lightweight, flat or curved roof system in residential, light commercial and industrialbuildings. Thickness/span details for a structural, non-trafficable plywood roof system to supportlightweight roofing are given in table 9. If the roof is to be trafficable, then the plywood must betreated as a floor and design data sourced from the EWPAA design manual “T&G StructuralPlywood for Residential Flooring” available from the EWPAA Web Site. The T&G plywood providesa structural diaphragm and eliminates the need for other forms of bracing in the roof system. Thedesign of plywood diaphragms is covered in Appendix J of AS/NZS1720.1 Timber Structure Code.Installation of Structural Plywood Roofing SystemPlywood SpecificationThe plywood to be used is CD or DD grade T&G structural plywood to AS/NZS2269. Specialised T&Gplywood with a decorative underside, usually V grooved to give a planked effect, can be used as acombined structural roof and decorative ceiling. Square edged plywood can be used but will requirenogging under the side joints.Roofing OverlayThe roofing overlay must be waterproof and durable. It may be decorated asphalt or fibreglassshingles, timber shakes or shingles, rubber, acrylic or bitumen membranes or metal tiles or decking.InstallationThe two major requirements for the T&G structural plywood are the face must run across i.e.perpendicular to, the rafters or trusses, and the plywood must be continuous over two or morespans. The plywood should be installed with 2-3mm gap at all sheet edges, the appropriate fixingsare given in Table 8, and the minimum plywood thickness relative to truss or rafter spacing arelisted in Table 9.20
Table 8: Fixing of T&G Structural Plywood to Non Trafficable RoofsDesign speed(permissibleStress)33 metres/second41 metres/secondNon CyclonicMinimum Fastener2.8mm dia. X 50mmFlathead NailsNo. 8 x 40mmCountersunk selfdrilling wood screws3.05mm dia. X 50mmFlathead NailsNo.8 x 40mmCountersunk selfdrilling wood screwsFastener Spacing at End and Intermediate Supports (mm)General roofs areasWithin 1200mm of RoofPerimeters150 100150 100100(for 1200mm spans)150(for 900mm & 800mm spans)50(for 1200mm spans)75( for 900 & 800mm spans)150 100Notes:1. The above fixings are applicable to timber species with joint strength J4 and JD4 and to plywood up to21mm in thickness.2. For higher wind speeds or cyclone sites fixings are to be designed for uplift in accordance withAS/NZS1170.2 “wind actions”.Table 9: Allowable structural plywood thickness and rafter spacing for plywood non-trafficableroofs supporting light weight roofing systems (20kg/m 2 max.)Rafter or TrussSpacing (mm)Minimum Allowable Plywood Thickness (mm)F8 F11 F14800 13 12 12900 16 15 151200 19 17 1621
Page 4 and 5: Face QualityPlywood can be ordered
Page 7 and 8: Curving PlywoodPlywood can be safel
Page 9 and 10: Lightweight panelsPlywood is strong
Page 11 and 12: Plywood Exterior CladdingPreservati
Page 13 and 14: It is essential in plywood cladding
Page 15 and 16: Corner Joint Details15
Page 17 and 18: Plywood Interior Wall & Ceiling Lin
Page 19: Bracing Resistance of Plywood Wall
Page 23: EWPAA MembersPlywood and Laminated

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