Timeline Of How The Leaky Homes Scandal Was Allowed To Happen

Careful analysis of the documentation and the chronology reveals how the government allowed changes in timber treatment, building practices, building materials and inspections which were responsible for the ‘leaky homes’ scandal.

Perhaps the bigger scandal is that the government never accepted responsibility for its role in this, instead, placing much of the blame on the builders.  While this is in part justified, a more apt label might be the “untreated timber” scandal, which was the primary cause of most of the damage to the buildings of the day.

Loss of Timber Treatment

  • 1952

    Boron Enquiry Approved Boron at 1.2% BAE for all wood destroying pests

    0.1% controls borer
    0.48% controls most fungi
    0.76% controls common termites
    1.2% gave a safety factor

    Approved provided the timber had adequate ventilation.

    All wood-destroying pests controlled 


  • 1975

    Boron Treatment Levels Lowered to 0.8% BAE, Stucco houses required tanalith (CCA) bottom plates

    NZS 3602:1975 was introduced

    A loading charge of 3.2kg/m3 of boron was specified which resulted in 0.8% BAE cross-sectional loading and 0.1% BAE at the core after six weeks.

    The reduction in BAE was justified by better treatment processes.

    Timber treated to this level was classified as C8 “insect and low decay hazard”.

    All wood-destroying pests controlled 


  • 1988

    Change Hazard Classes to Match Australian Classification: H1 - H6. No Effective Change in Framing Timber Treatment

    The existing NZ boron treated C8 “insect and low decay hazard”  classification should have been matched to the Australian H2 “termites and low decay” classification but boron had not been approved in Australia so H2 was not produced.

    Instead, the NZ mills produced H1 but maintained the old C8 treatment levels, now specified at 0.1% boron in the central ninth (core).  Effectively H1 boric of this era was identical to C8.

    All wood-destroying pests controlled 


  • 1992

    H1 Treatment Changed to Allow 0.1% BAE Wet, 0.04% BAE Dry, or Permethrin

    This was the first real change to timber treatment levels.

    0.1% BAE wet provided a small amount of protection against decay whilst 0.04% BAE dry and Permethrin only protected against insects.

    No,or minimal protection against decay or termites

    Some protection against borer, provided the timber remains dry


  • 1990’s

    Timber Producers Lobby to Use Kiln Dried Timber

    Carter Holt Harvey and other timber producers lobbied to use untreated kiln dried timber supported by research on 1950’s homes built with untreated pine.  However these were traditional weatherboard houses with cavities, eaves and good weatherproofing, and the timber was durable heartwood pine.  Current houses had none of these safeguards and the pine was cheaper, softer sapwood.
    No research and testing was carried out on current timber using current construction methods and house designs.


  • 1994

    BRANZ Appraise (Approve) H1 For Use Without Limitation, While Their Research Shows Even Well Treated Timber Rots

    H1 appraised as suitable for all framing and without limitations, such as requiring ventilation.

    BRANZ research showed that even well-treated 30-year-old stucco houses had serious decay problems.

    Borer was controlled, Decay was not controlled.


  • 1998

    BRANZ Appraisal Undated to Allow Untreated Kiln Dried Timber (0% BAE)

    BRANZ Appraisal 279A Appraising untreated timber.

    Use of Untreated Kiln Dried Timber becomes widespread.

    Neither borer nor decay were controlled and problems emerged rapidly


  • 1998

    The Building Industry Authority Allows Untreated Pine as Part of an Acceptable Solution

    Once this is part of an Acceptable Solution, the local councils are legally required to accept this.  Although theoretically only allowed if the moisture level stayed below 18%, in practice this was impossible to achieve.

    Untreated timber now became the normal framing timber used


  • 2002

    Auckland City Council Practice Notes Require H1 Plus Treated Timber

    The ACC were advised by the BIA in 2002 that untreated timber was not compliant. The council produced Practice Notes requiring H1 Plus timber, which was treated with either boron (0.4%) or LOSP.

    However, the Notes were not applied consistently at the start – typically just to ‘high-risk’ houses and many houses currently under construction or already consented were allowed to be built with untreated timber.

    Some houses now built with treated timber but other allowed to use UTKD timber.


  • 2003

    New Acceptable Solutions include return to treated timber - H1.2 0.4% BAE Cross Sectional Loading

    BRANZ advise that old Appraisals have been superseded and issued Appraisal 243.

    H1.2 is moderately loaded with boron, which will leach out with leaks and isn’t strong enough to withstand native termites.

    Moderate control of decay and insects


Loss of Building Standards

  • Past

    Treatment, Cavities and Effective Flashings, Including Eaves Were Standard Building Practices

    By building houses that were treated, ventilated and well protected, if one of these failed, the other safeguards meant that the house was still safe, and wouldn’t rot before it could be maintained.

    Timber is protected from the weather and can dry if the house leaks.

  • 1972

    Aluminum Windows Without Undersill Trays Introduced

    Traditional wooden windows had undersill trays which collected any leaks and directed them out of the house.  The aluminium windows did not, allowing water into the house. As the windows age, the mitres, joints and sealants fail increasing the leakage.

    The timber at this stage was well treated and was ventilated, so there were not many decay problems.

    Loss of weathertightness

  • 1978

    Government Mandate Insulation - Harder to Ventilate the Framing

    Many builders didn’t change construction techniques and many continued building walls without ventilation – i.e. enclosed framing.

    Ventilation and drying now restricted many houses.

  • 1983

    BRANZ Research Shows Enclosed Framing Cannot Dry and Must Not Be Allowed

    This research was presented to the World Durability Conference in 1983 but is not made public.

  • 1985-2003

    BRANZ Appraise Dozens of Face Sealed Claddings Without Proper Flashings or Testing

    BRANZ is the accepted authority and these cladding are now adopted by architects, specifiers and builders.  Councils approve them in Building Consents and issue Code of Compliance Certificates for completed houses. Together with poor weathertightness detailing, no cavities and untreated timber, virtually all of these claddings leak and the leaky homes crisis is here.

  • 1986

    BRANZ Tests on Window Leakage Showed all Windows Leaked

    All aluminium windows, including those with undersill trays, leaked.

    Houses no longer protected from the weather and leaks are inevitable.

  • 1992

    BIA Approves Enclosed Framing for Stucco Rigid Backing

    Approved as part of Acceptable Solution E2/AS1.  BIA did not exclude using undertreated H1 for external framing and it continued to be used, even when the treatment levels of H1 had been reduced.

    Undertreated H1 now used enclosed behind unventilated stucco and other face fixed cladding.  Timber decay was inevitable and predictable.

  • 1994

    BRANZ Research Finds Serious Decay in 30 Year Old Stucco Homes

    Even though these were built from very well treated timber and with tanalised bottom plates, these still decayed well short of the 50 year expected durability.  Information was published in the Good Stucco Guide.

  • 1994

    Private Certifiers Allowed to Inspect and Approve Building Work

    In the 1991 Building Act, councils lost their monopoly on inspecting and approving building work, however, the certifiers could not get adequate insurance.

    Many homeowners could not get a compliant CCC, or could not sue the negligent certifier.  The scheme fell over and control returned to the councils leaving many homes in limbo.

  • 2002

    BRANZ Weathertightness Tests Fail All Face Fixed Claddings

    When BRANZ develops a weathertightness test for claddings, even those previously appraised as acceptable fail without a cavity.

    Tens of thousands of faulty houses have already been built with untested, unsuitable cladding.

  • 2002

    Auckland City Council Product Practice Notes Required Cavities, H1 Plus Treated Framing etc

    Following advise from the BIA, these practice notes are produced promoting a return to the traditional belts and braces. These were selectively applied to more at-risk buildings, allowing many other homes to be completed and issued CCC without knowing that the timber, and construction methods were now proven to fail.

    Improved treatment, details and inspection results from houses subjected to these practice notes

    Houses perceived as low-risk were still built with untreated timber and no cavities.

Moisture Detection Company designed and patented the Mdu Moisture Detection Probe in 2005 to find the leaks and damp timber resulting from poor construction, design and the lack of cavities.  These have been installed in thousands of houses.

The extensive use of undertreated and untreated timber left thousands of homes vulnerable to serious decay so RotStop was designed to post-treat timber and put the decay process on-hold.  RotStop is the only effective way that homeowners can protect their framing timber without a full re-clad.