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Substrate

When plywood substrate is used beneath fully supported roof cladding, it should be smooth and dimensionally stable, with a moisture content of less than 18% and made windtight. All screws should be countersunk to prevent damage to the metal cladding.

Plywood with a minimum thickness of 12 mm should be fixed to the framing at 600 mm centres, with 40 mm x 8# countersunk screws at 150 mm centres around the panel edges and 200 mm centres on the intermediate supports. The fasteners should not be closer than 10 mm to the edges.

Although 17.5 mm plywood will span 1200 mm, the length of the fasteners should be increased proportionately.

A 3 mm expansion gap should be provided between sheets and a nail or screw can be placed in the gap and be used as a spacer for this purpose. All joints should be staggered and taped over before placing the underlay.

Framing centres should be designed to withstand the increased loads at the periphery of the building.

 

Ventilation must be provided for all fully supported roof designs using plywood substrate. See Ventilation.
CCA treated plywood must not be used under zinc, aluminium, metallic coated or prepainted steel cladding without an underlay complying with Underlay Suitability or without being separated by an underlayment. Provision must be made for adequate ventilation under the sarking.
Where the design wind load is higher than 1.5kPa, the minimum fixing centres for 12 mm ply substrate must be 400 mm.
Clause: 
015_004_004_002_000_000_000_000_000
Clause Number: 
15.4.4.2
/cop/other-products/standing-seam-cladding#substrate
Revision Category: 
0 - Clause Removed
Revision Detail: 

Clause removed during a comprehensive revision of Standing Seam Cladding.

Draft Clause: 
014_004_004_002_000_000_000_000_000