Timber slat decks – rot to deck joists/bearers

Cause

The timber treatment was not adequate

Repair

  • take the deck apart and replace all rotten or damaged timber. Pinus radiata should be treated to minimum H3.2 (or replace with a naturally durable species). Deck joists and bearers must have 50-year durability. Use timber grade of at least SG8 (wet in service). Joist sizes can be found in NZS 6014:2011 Table 7.1(b). Bearer sizes can be found in Table 6.4(b)

  • select metal fixings with at least the same durability requirements as the timber they connect. (NZS 3604:2011 Timber-framed buildings has the details in section 4.4). Steel fixings in ‘sheltered’ locations – open to airborne salts but not rain washed – must typically be galvanised as a minimum. Those in ‘exposed’ locations – open to airborne salts and rain – require Type 304 or 316 (for marine exposure) stainless steel

  • the bearer-to-pile connection should be M12 bolt with 50 × 50 × 3 mm washer (or 12 kN connection)

  • for decks more than 1 m off the ground that were built after 1992, a building consent will be required for the repair/rebuild where the minimum durability period was not achieved. All new work must be building code compliant

  • details for decks can be found in this Build magazine supplement

Cause

The timber is at the end of its serviceable life

Repair

  • repair as above

Cause

Moisture remains trapped in the junctions of framing

Repair

  • repair as above