Acceptable Standards of Domestic Construction

Transcription

1 Truss or Rafter Roof Batten Triple grip fastener (for roof trusses) Foil lined Insulation blanket Top plate Sprocket Brick tie Top plate strapping at 1200mm max. cts. Note: Holding down straps should be not less than 900mm down the cavity and turned into brick joint a minimum of 50mm Ventilated soffit Soffit bearer Fascia Flashing Galvanised lintel Window frame Brick sill Sill flashing Brick tie Bearer Floor joists Flashing Ant capping continuous for full thickness of wall Air vent DPC under ant cap Ground line Figure 10.2: Cross Section Through Cavity Masonry Wall 54 Acceptable Standards of Domestic Construction

2 10.2 GALVANISED STEEL STRAPS Window and door frames BCA Housing Provisions Part Unless provision is incorporated in the frames, fix all door and window frames in position with 32 x 0.8 mm galvanised steel straps secured to frames and set at least 300 mm into brickwork. Space straps at a maximum of 400 mm. Holding-down straps AS3700, AS1684, AS4055 When used to hold down timber plates, rafters or beams on brickwork, 32 x 0.8mm galvanised steel straps must be spaced at 1200 mm centres (maximum) for tile, sheet roofing or decked roofs. Continue these straps not less than 900 mm down the cavity with ends turned 50 mm into brickwork, and the upper ends turned over plates and nailed with 3 x 30 x 2.8 nails or appropriate fixings. Secure the ends of verandah plates similarly. Where no top plates occur (eg. brick piers), or where trusses or roof framing are positioned directly on brickwork, fixing plates or straps must be provided. These must be secured and spaced as required by the manufacturer or in compliance with AS or AS4055 and, if timber framing is used, additional compliance with AS1684 and AS3700 is required. Note: For exposed/high wind areas a reduction in spacing and increase in tie length is required CAVITY FLASHINGS BCA Housing Provisions Part 3.3.4, AS2904 Build in cavity flashings of 10 kg/m lead, bitumen coated non-ferrous metal or other acceptable material, at locations where the cavity is crossed (eg. By doors, windows, ducts, meter boxes), or where a wall cavity terminates above an internal portion of a building or at any location where moisture needs to be drained from a cavity. Refer to 8.4: s. Do not penetrate flashings with services. Note: Lead cannot be used on any roof which is part of a potable water catchment area. Overflashing Weep hole 75mm lap Weep hole Minimum 75mm flashing overlap (where two-piece flashing used) Apron/soaker flashing Anchor bolt 75mm apron flashing turned up behind overflashing Figure 10.3: Typical Stepped Cavity Flashing Acceptable Standards of Domestic Construction 55

3 Ceiling Joist Roof Batten Rafter Foil lined insulation blanket Fascia Top plate Top plate strapping at 1200mm max. cts Lintel Eaves lining Clearance at window head Flashing Soffit bearer Sill plate Internal linning Flashing turned up behind sill Cladding Sarking Bearer Floor joists Bottom plate Blocking Ant cap DPC under ant cap Air vent (between piers) Engaged pier Ground line Concrete footing Figure 10.4: Cross Section Through Timber Frame Wall Acceptable Standards of Domestic Construction 59

4 11 ROOF CONSTRUCTION BCA Housing Provision Part 3.4 Roof construction materials and methods other than those described in Section 11.1 of the handbook may only be used with approving/certifying authority approval. Both trussed and conventionally framed roofs are to be adequately tied-down to the walls CONVENTIONAL TIMBER ROOF FRAMING Single Storey and Two Storey Dwellings AS1684, AS1720, AS4055 Refer to the span tables (see Appendix 4) for rafter sizes for use in typical single or two storey dwellings. Both trussed and conventional framed roofs are to be tied down to the walls. Pitch roof Rafters must be: Set out to give full tile course to the longest ridge. Neatly cut at junctions with ridges, hips and valleys, bird s-mouthed over plates and securely fastened to ceiling joists and top plates. Fixed using proprietary nailing plate and straps in exposed locations. Ridge Battens 25mm min. Collar tie Strutting beam supported off loadbearing walls Detail A Ceiling hanger Roof tiles Maximum angle for roof struts is to be less than 30 degrees Anti-ponding board if sarking is to be installed Detail B Hanger ties Timber frame Internal wall Figure 11.1: Typical Timber Framed Roof Structure Brick tie Brick veneer Soffit lining Acceptable Standards of Domestic Construction 69

5 Rafter Collar tie 10mm bolt Purlin Struts must not bear on ceiling joists, only on walls or strutting beams 30 max Hanging beam Secure hanging beam to ceiling joist with ceiling dogs or hoop iron on alternate sides Ceiling Top plate Stud Ceiling joist Ceiling plaster cornice Ceiling batten Figure 11.2: Typical Roof Construction Detail A & B Where ceiling joists run at right angles to rafters, rafters must be tied to prevent the roof spreading. Hanging/strutting beams or strap bracing ties at ceiling level can be used for this purpose. Prefabricated timber roof trusses AS4440, AS1720, AS1684, Prefabricated roof trusses must be fabricated in a properly equipped factory and fixed in strict accordance with a structural engineer s details and specifications, and approved by the approving/certifying authority. Each truss must be suitably branded to identify the manufacturer, with at least one main truss branded with the design number and specification requirements of the trusses supplied to the dwelling. Trusses fabricated on site to an engineering specification require certification. When placing trusses in position, leave a minimum clearance of 12 mm between the truss and top of internal walls. Use self-adjusting fasteners to fix internal walls to the truss, to allow for long-term truss deflection. Use galvanised nailing plates for truss fixing to external walls. To support ceiling linings and minimise potential cracking, additional trimming to the roof frame is required every change in direction of the roof truss. Do not place any load such as hot water tank, solar heater or air-conditioning unit on the trusses unless the trusses have been specifically designed to carry the loads. 70 Acceptable Standards of Domestic Construction

6 Tiles Sarking fixed under battens Framing anchor 4.5mm fibre cement anti-ponding board Sarking Bulk insulation Sprocket every 3rd rafter Ventilated soffit Wall plate strapping at 1800mm maximum centres fixed to rafter Wall tie Figure 11.3: Typical Eaves Detail for Tiled Roof Foil lined Insulation blanket Roof sheeting Ventilated soffit Soffit bearer Tie-down strap over rafter 10mm Wall tie Vapour barrier Figure 11.4: Typical Eaves Detail for Sheet Roofing 72 Acceptable Standards of Domestic Construction