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Wood Preservation in NZ. Regulations promulgated in 1955Timber Preservation Authority establishedGovernment agency which approved treatments, set standards and registered plantsState Advances Corporation controlled most housing mortgages. Housing. SAC required treatment of framing lumber to TPA SpecsMain threat was insect (borer attack)Boron diffusion treatment and framing erected wetFungicidal as well as insecticidalDry framing requirement 1990sLOSP insecticides (SPs) introduced.
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1. 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 * Ensis is a Joint Venture between Forest Research NZ & CSIRO Australia * Ensis is a Joint Venture between Forest Research NZ & CSIRO Australia
2. 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
3. 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
4. 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
13. Problem Buildings Problem mainly associated with monolithic claddings
Complex designs
No eaves
Parapets
Many junctions requiring sealants
Enclosed balconies
Inadequate or no flashings
14. 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
15. 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
16. 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
17. “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
18. 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
34. 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 (<20%)
35. Implementing Research Results Effective treatments identified from trials
Preservatives registered with regulatory authorities
Amend preservative (NZS 3640) and timber utilisation (NZS 3602) standards
36. 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
37. 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.
38. 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
39. 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
40. 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
41. 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
42. 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
43. MC/time/decay effects on stiffness Pre-conditioning
Equilibrated at 16% emc
Wet to >35 % MC
Measure deflection (3 point load)
Inoculate with decay fungi
Visually asses for decay and re-measure deflection over time
53. Conclusions Visual assessment tends to overstate actual decay and stiffness loss
Decay fungi remain alive on wood at 18 % mc but will not attack
54. Relative Durabilities of Framing Options Test relative durabilities of treated and untreated framing options included in NZS 302
Untreated and preservative treated
61. 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
62. 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
63. 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