Timber slat decks – rot to deck joists/bearers
Listed under: Exterior, timber and wood-based, timber, decks, framing, durability, rot
Cause
The timber treatment was not adequate
Repair
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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)
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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
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the bearer-to-pile connection should be M12 bolt with 50 × 50 × 3 mm washer (or 12 kN connection)
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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
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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