Rot in timber weatherboards

Cause

Timber is or has been continuously damp

Repair

  • determine and address cause of continuous dampness of timber
  • remove rotten section(s) of weatherboards:
    • splay (slant) cut back to nearest studs (at least 600 mm in both directions)
    • treat cut ends of existing boards with paint-on preservative
    • prime cut ends of timber
    • insert new boards
    • ensure that back face and ends of timber are primed
    • nail edges of existing and new boards to studs using one nail per stud and board
    • prime
    • fill joints with putty or exterior grade flexible (polyester) filler
    • paint with at least two coats of semi-gloss or high gloss acrylic paint
  • before replacing boards, check that wall underlay (building paper) and framing behind weatherboards are sound
  • if timber cladding is in ground contact, ensure there is at least a 100 mm gap to paved ground and 175 mm gap to unpaved ground to prevent moisture uptake
  • if a weatherboard is badly affected by rot it may be easier to replace the entire board rather than trying to partially replace board
  • where it is suspected that the building may be leaking and there is a risk of damage behind the cladding, engage an experienced New Zealand Institute of Building Surveyors (NZIBS) building surveyor to report on the building

Cause

Timber was inadequately treated – radiata pine must be treated to H3.1 if painted and H3.2 if installed unpainted or stained

Repair

  • remove rotten section(s) of weatherboards:
    • splay (slant) cut back to nearest studs (at least 600 mm in both directions)
    • treat cut ends of existing boards with paint-on preservative
    • prime cut ends of timber
    • insert new boards
    • ensure that back face and ends of timber are primed
    • nail edges of existing and new boards to studs using one nail per stud and board
    • prime
    • fill joints with putty or exterior grade flexible (polyester) filler
    • paint with at least two coats of semi-gloss or high gloss acrylic paint
  • before replacing boards, check that wall underlay (building paper) and framing behind weatherboards are sound
  • if timber cladding is in ground contact, ensure there is at least a 100 mm gap to paved ground and 175 mm gap to unpaved ground to prevent moisture uptake
  • if a weatherboard is badly affected by rot it may be easier to replace the entire board rather than trying to partially replace board
  • where it is suspected that the building may be leaking and there is a risk of damage behind the cladding, engage an experienced New Zealand Institute of Building Surveyors (NZIBS) building surveyor to report on the building

Cause

Non-durable or untreated timber was used – timbers such as cedar and heart macrocarpa may be untreated but they must not be continuously wet in use

Repair

  • remove rotten section(s) of weatherboards:
    • splay (slant) cut back to nearest studs (at least 600 mm in both directions)
    • treat cut ends of existing boards with paint-on preservative
    • prime cut ends of timber
    • insert new boards
    • ensure that back face and ends of timber are primed
    • nail edges of existing and new boards to studs using one nail per stud and board
    • prime
    • fill joints with putty or exterior grade flexible (polyester) filler
    • paint with at least two coats of semi-gloss or high gloss acrylic paint
  • before replacing boards, check that wall underlay (building paper) and framing behind weatherboards are sound
  • if timber cladding is in ground contact, ensure there is at least a 100 mm gap to paved ground and 175 mm gap to unpaved ground to prevent moisture uptake
  • if a weatherboard is badly affected by rot it may be easier to replace the entire board rather than trying to partially replace board
  • where it is suspected that the building may be leaking and there is a risk of damage behind the cladding, engage an experienced New Zealand Institute of Building Surveyors (NZIBS) building surveyor to report on the building

Cause

Paint coating has failed

Repair

  • remove rotten section(s) of weatherboards:
    • splay (slant) cut back to nearest studs (at least 600 mm in both directions)
    • treat cut ends of existing boards with paint-on preservative
    • prime cut ends of timber
    • insert new boards
    • ensure that back face and ends of timber are primed
    • nail edges of existing and new boards to studs using one nail per stud and board
    • prime
    • fill joints with putty or exterior grade flexible (polyester) filler
    • paint with at least two coats of semi-gloss or high gloss acrylic paint
  • before replacing boards, check that wall underlay (building paper) and framing behind weatherboards are sound
  • if timber cladding is in ground contact, ensure there is at least a 100 mm gap to paved ground and 175 mm gap to unpaved ground to prevent moisture uptake
  • if a weatherboard is badly affected by rot it may be easier to replace the entire board rather than trying to partially replace board
  • where it is suspected that the building may be leaking and there is a risk of damage behind the cladding, engage an experienced New Zealand Institute of Building Surveyors (NZIBS) building surveyor to report on the building