Fence rails sagging

Causes

Timber deflection over time

Posts too far apart

Rail too small for post spacing

Timber has rotted

Fixings corroded

Listed under: timber and wood-based, timber, Section, fences, durability, rot, fixings and hardware, fixings

Cause

Timber deflection over time

Repair

  • where the appearance is visually unacceptable, replace with new rails. H3.2-treated radiata pine rails are readily available. Specify rails no smaller than 100 x 50 mm. As a minimum protection, fix to posts with hot-dip galvanized nails with an annular grooved shank, or stainless steel in very corrosive environments (close to the sea or in a geothermal area)
  • dark-coloured finishes on timber attract heat from the sun and resulting temperature extremes can cause unwanted changes in timber shape over time. Using lighter-coloured finishes (or no finish at all) will reduce the risk of movement

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Cause

Posts too far apart

Repair

  • install new intermediate posts or replace existing posts with new at more effective distances. H4-treated radiata pine posts are readily available. For a strong fence, posts should be no more than 1800 mm apart. For fences up to 1800 mmm high, ensure the holes are at least 750 mm deep and the posts are set in concrete

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Cause

Rail too small for post spacing

Repair

  • replace with larger rails – 100 x 50 mm is a common size and is sufficient in most locations where posts are 1800–2400 mm apart. H3.2-treated radiata pine rails are readily available

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Cause

Timber has rotted

Repair

  • replace the rotted rails. H3.2-treated radiata pine rails are readily available
  • where rot is the result of continuously wet timber from overhanging trees, consider trimming the trees to let more drying breezes through

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Cause

Fixings corroded

Repair

  • install new fixings – hot-dip galvanized nails, or stainless steel in very corrosive environments (close to the sea or in a geothermal area). Nails with an annular grooved shank will have better holding power. Where nails are close, stagger the position to reduce the risk of timber splitting

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