Plywood Substrate Specification

Plywood is used as the substrate for all roofing and wall-cladding profiles installed by The Architectural Roofing Company. This includes Variable Tray, Snap-lock and custom profiles. The final finish of the cladding and roofing profile can be inversely affected by the incorrect installation of the plywood substrate.

1. Plywood should be CPD that is constructed ply, plugged and sanded on the upper face.
2. Plywood must be H3 treated. Treatment must be water based.
3. We prefer plywood to be 15mm T & G, if unavailable; an allowance is to be made of 3mm between sheets for expansion and contraction.
4. Plywood substrate should be a minimum of 12mm. It should be laid with the face grain at right angles to the support.
5. Plywood must be screw fixed with countersunk self-drilling screws. Screws should be corrosion resistant (stainless steel) preferred and spaced at 150mm on edges and 200mm on internal purlins. Nails, staples or other forms of fixing are not to be used.
6. For rafters at 900mm centres it is recommended to use 75x 50 mm purlins on flat, at 600mm centres. All plywood edges should be fully supported.
7. At the gutter line plywood should overhang the fascia board by at least 20mm. This in conjunction with our drip edge allows for correct 60mm runoff into an external gutter. The edges are to remain square cut.
8. Where the roof terminates into a membrane type gutter or roof the plywood planes should finish flush. There should be a minimum of a 50mm upstand separating the two planes.
9. Use string lines to ensure all ridges, hips, and valleys run true and straight.
10. Once plywood is fixed sweep down all surfaces to ensure no debris remains.