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

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

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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