Past and Current Research at Ensis on Timber Framing Durability Issues Mick Hedley, Senior Scientist

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Past and Current Research at Ensis on Timber
Framing Durability Issues - Mick Hedley, Senior
Scientist,Wood Processing and Products

• Leaky Buildings Symposium Causes and Solutions
• Auckland 18-19 July 2005

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Wood Preservation in NZ

• Regulations promulgated in 1955
• Timber Preservation Authority established
• Government agency which approved treatments, set
  standards and registered plants
• State Advances Corporation controlled most
  housing mortgages

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Housing

• SAC required treatment of framing lumber to TPA
  Specs
• Main threat was insect (borer attack)
• Boron diffusion treatment and framing erected wet
• Fungicidal as well as insecticidal
• Dry framing requirement 1990s
• LOSP insecticides (SPs) introduced

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Background to Decay Problems in NZ Housing

• Kiln-dried untreated framing introduced mid-1990s
  based on results of surveys of 1950s housing
  which showed little borer attack in untreated
  framing
• Current trend for monolithic cladding is NOT the
  building style on which conclusions were reached
  that untreated, kiln-dried is an acceptable
  alternative to treated
• The new problem is lack of weathertightness

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Problem Buildings

• Problem mainly associated with monolithic
  claddings
• Complex designs
• No eaves
• Parapets
• Many junctions requiring sealants
• Enclosed balconies
• Inadequate or no flashings

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Problem Buildings

• Estimated 60 of new buildings leak
• Inability of cladding panels to prevent external
  water entering the framework where it is unable
  to dry
• Building Code requirement is for framing timber
  not to exceed 18 moisture content

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The Dilemma

• No adequate definition of the decay hazard for
  framing
• An industry requirement for dry framing
• Options if treatment were to conform with current
  standards
• H3 treatment with TBTN, TBTO, CCA, ACQ or CuAz

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Proposed Solution

• Introduce specific treatment requirements for
  framing timber
• Not seen as permanent protection should timber
  remain wet for extended periods
• Temporary protection until any leaks are detected
  and rectified

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H1 Plus Concept

• In 2002, Exterior Insulation and Finish Systems
  (EIFS) manufacturers proposed some level of
  fungicidal preservative treatment for exterior
  wall framing
• Informal and called H1 Plus
• Had support of preservative suppliers
• Informality made it impossible to include in
  Building Code or NZ Standards
• Encouraged commencement of testing programme

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Test Protocol to Assess Framing Treatment Options

• Experimental design
• Simple design which would test preservative
  systems, not preservatives
• Use realistic timber sizes (90 x 45 mm) of
  commercial framing quality
• Use standard building materials
• Limited control of moisture content
• Accelerate decay by pre-inoculating

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Assembled Unit
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Untreated 25 weeks
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Untreated 25 weeks
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Untreated 3 years exposure
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IPBC treated 2 years exposure
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Same unit as previous slide dissected
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Building Code Final Draft

• Further revision has introduced specific
  preservation requirements for framing timber used
  in high risk buildings
• Not seen as permanent protection should timber
  remain wet for extended periods
• Temporary protection until any leaks are detected
  and rectified
• Long term durability must rely on framing
  remaining at low MC (lt20)

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Implementing Research Results

• Effective treatments identified from trials
• Preservatives registered with regulatory
  authorities
• Amend preservative (NZS 3640) and timber
  utilisation (NZS 3602) standards

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NZ Hazard Class System

• H1 - protected dry (wood borers)
• H2 - protected dry (borers/termites)
• H3 - outside, above ground
• H4 - outside, in ground
• H5 - outside, in ground, critical use
• H6 - marine environment

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Hazard Class ?

• For international conformity, treatment to confer
  decay resistance to framing would preferably be
  within the definition of Use Class 2 of the
  proposed ISO standard
• Situations in which wood or wood-based products
  are under cover and fully protected from the
  weather, but where high environmental humidity
  or water ingress can lead to occasional but
  not persistent wetting.

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Hazard Class ?

• Or equivalent to AWPA Use Category 2
• Wood and wood based materials used for interior
  construction that are not in contact with the
  ground, but may be subject to dampness

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Hazard Class ?

• Hazard Class H2 in Australasia makes no allowance
  for temporary wetness nor for a decay hazard
• Inside, above ground. Protected from wetting. Nil
  leaching.
• Wood borers and termites are the only biological
  hazards recognised in H2

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Hazard Class H1.1 and H1.2

• Only practical option was to divide H1 into two
  sub-classes
• H1.1 No risk of temporary wetting - biological
  hazard is insect borers only
• H1.2 At risk of attaining a moisture content
  conducive to decay - biological hazards are
  insect borers and decay

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H1.2 Approved Preservative Treatments

• Boron
• cross-section 0.40 BAE m/m
• TBTO/TBTN
• cross-section 0.06 Sn m/m
• IPBC (permethrin)
• cross-section 0.025 IPBC m/m
• Full sapwood penetration, no requirement for
  heartwood penetration

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Conclusions

• Test protocol accepted by regulatory authorities
  which approve treatments
• Cannot simulate all exposure situations
• Maybe too conservative, i.e. may exclude some
  effective treatments

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MC/time/decay effects on stiffness

• Pre-conditioning
• Equilibrated at 16 emc
• Wet to gt35 MC
• Measure deflection (3 point load)
• Inoculate with decay fungi
• Visually asses for decay and re-measure
  deflection over time

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Conclusions

• Visual assessment tends to overstate actual decay
  and stiffness loss
• Decay fungi remain alive on wood at 18 mc but
  will not attack

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Relative Durabilities of Framing Options

• Test relative durabilities of treated and
  untreated framing options included in NZS 302
• Untreated and preservative treated

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Larch sapwood before installation, Antrodia
xantha feeder block attached to joint end.
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Top layer, Tank 1, 26 weeks exposure. Decay
becoming established on D. fir and Lawsons
sapwood
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Layer 2, Tank 1, 38 weeks exposure.Moderate/severe
decay in all samples which have extensive
mycelium growth (larch, D. fir and Lawsons
sapwood).
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Conclusions

• Untreated radiata pine sapwood most susceptible
  to decay
• Other species less easy to wet to moisture
  content high enough to support decay
• Treated more durable than untreated

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General Conclusions

• Preservative treatment of framing will NOT solve
  the problem of leaking buildings
• It will NOT prevent subsequent damage to linings,
  fixings, coverings etc which are susceptible to
  damage when wetted, if buildings continue to leak
• It will NOT prevent mould growth associated with
  excessive moisture in buildings

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General Conclusions

• Preservaive treatment of framing would reduce
  remediation costs
• It would considerably reduce the risk of
  structural failure from decay
• Current treatment options are H1.2 or H3
• Optimum requirements for treatment of framing
  which maybe at risk from decay, particularly
  during the construction phase, have not been
  conclusively established