Support for plywood clarified

The Department has received a number of queries about installation requirements for plywood substrates under membrane roofs and decks, as outlined in Acceptable Solution E2/AS1, Paragraph 8.5.5.1. The main concerns are about sub-paragraphs (c) and (d).

These paragraphs state that plywood substrates need to be fixed according to the following requirements.

• (c) The maximum span shall be 400 mm.
• (d) Plywood shall be laid with the face grain at right angles to the supports.

In other words, either the primary or secondary framing supports must be at a maximum of 400 mm centres, and the plywood substrates must be laid with their grain or long dimension at right angles to the framing supports.

These requirements are illustrated in Figures 1 and 2 below.

In Figure 2 secondary supports, such as nogging or dwangs, need to be installed in accordance with NZS 3604 or to a specific engineering design.

Refer to E2/AS1 Paragraph 8.5 for other installation requirements for plywood substrates.