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.

Moisture Detection Company developed systems and products to diagnose and overcome many of the problems faced by plaster homeowners as a result of this disaster.

Loss of Timber Treatment

  • 1952

    Boron Enquiry Approved Boron at 1.2% BAE sufficient to control 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 and was not in contact with absorbent cladding which leach out boron when wet

    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”.

    Required adequate ventilation of the framing and no contact with absorbant claddings.

    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.

    H1 had to be protected by external walls, i.e. should only have been used for non-load bearing internal walls.  Everyone became accustomed to using this everywhere because is was well treated.

    All wood-destroying pests controlled 


  • 1992

    H1 Treatment Changed to Allow 0.1% BAE Wet, 0.04% BAE Dry, or Permethrin (MP3640:1992)

    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.

    H1 must be protected by external walls.  H1 was not a specification for external wall framing.

    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 for internal walls.  This was 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, including external walls. Their Research Shows Even Well Treated Timber Rots

    H1 appraised as suitable for all framing including enternal walls,  and without limitations such as requiring ventilation for absorbent claddings.

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

    Borer was controlled, Decay was not controlled.


  • 1995

    NZS3602:1995 Approved Substitution of H1 with Untreated Timber

    BUT H1 framing was not approved for external walls. Untreated timber has never been approved for external walls even in Standards.  However councils continued to allow this to be used.

    No protection against decay, borer or termites.


  • 1998

    BRANZ Appraisal Updated to Allow Untreated Kiln Dried Timber (0% BAE) without limitations except must stay under 18% moisture content

    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 adopts NZS 3602:1995 Untreated Pine as Part of an Acceptable Solution

    This was adopted without limitation except for maximum in-service moisture content of 18%.  However there was no method to check the in-service moisture.

    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 AND assumes no need to comply with the Standards which precluded either H1 or Untreated pine on external walls.

    Untreated timber now became the normal framing timber used.  No control over insects or decay.


  • 2002

    Auckland City Council Practice Notes Require H1 Plus Treated Timber

    The ACC were advised in writing by the BIA in 2002 that untreated timber was not compliant with NZS 3602:1995.  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


  • 2007

    Moisture Detection Company Begin Treating Houses with Untreated Timber using "RotStop"

    An answer was required to assist home owners whose houses were framed with untreated (UTKD) or undertreated (H1) timber.

    Extensive research resulted in the proprietary RotStop product which contained boron, penetrants and various multispectrum fungicides which kill, control and prevent decay fungi.  Traditional surface applied treatments (e.g. Framesaver), proved ineffective against established decay, especially white rot fungi.

    Further research developed systems to direct inject RotStop into the timber or into the spaces between the studs and nogs.  This could be applied from outside (through the cladding) or inside (through the gib) with minimal damage or disruption.

    RotStop has successfully put the decay process on hold for ten years or more on many buildings with untreated framing.


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.

  • 2005

    Moisture Detection Company Design and Patent Mdu Moisture Detection Probes to Test Moisture Levels for Compliance

    Instead of proving compliance with the standards, the Mdu probes find widespread leaks, damp and rotting timber resulting from poor construction practices, poor weathertightness designs and lack of cavities.  Originally embraced by the industry as a tool to prevent another leaky home crisis, the probes prove an expensive embarrassment to councils and builders as they demonstrate that houses supposedly passed and given CCC are in fact leaking.

    The Mdu probe system is used to gather invasive testing evidence on hundreds of houses for proving leaky home claims against builders, architects and councils.

    Now that the time for homeowners to claim damages has passed, the Mdu probes are now used to find detailed data on leaks and decay so that house owners can plan appropriate maintenance.  Used in conjunction with RotStop, from Moisture Detection Company, expensive recladding can usually be avoided.

    Mdu Probes are read regularly as an early warning in case future leaks develop.

  • 2005

    Pre-Purchase Inspection (Builder’s Report) Standard Set As Visual Inspection Only

    The NZS4306:2005 Residential Property Inspection, dubbed ‘builders report’ or sometimes ‘pre-purchase report’ sets out the process to ‘visually inspect a building’. Courts have chastised this Standard as not ‘fit for purpose’ as it does not meet customers need to know whether the building is leaking or has damage (decay) from leaks.

    Section 4.2 of the Standard provides for ‘special purpose property inspection’ (n) ‘weathertightness’.  There is no instruction or process as to what a weathertighness inspection is, or what the outcome for the customer should be.

    Almost all ‘builders reports and pre-purchase inspections’ contain many legal disclaimers stating things like “cannot test in concealed spaces like external wall framing”, which is what purchasers want to know. Some inspectors use surface scanners and thermal imaging equipment which does not test moisture contents, treatment levels (if any) or decay. Some reports advise to carry out invasive testing but owners often refuse permission as traditional invasive testing is very destructive.

    Builder’s or Pre-Inspection Reports fail to provide house buyers with vital information about weathertightness, timber treatment levels or decay.  

  • 2005

    Auckland City Council Adopts Mdu Probes for All Reclad

    Mdu Probes became part of the reclad QA process to ensure that there were no more failures and defects had been corrected. Canada has buildings which had now been reclad three times. We did not want that to happen in NZ.

    Unfortunately, this was stopped very quickly as leaks and decay were found in buildings with newly issued CCC, creating huge future liability issues for the council.  If the leak isn’t discovered for ten years, the council liability lapses.

    New recladding procedures have been created however these do not include any way of monitoring the success of the reclad or detecting leaks that may start.

    No monitoring of the success or failure of reclad houses.

  • 2007

    Moisture Detection Company Offers Solutions to ‘Leaky Homes’

    Following thousands of houses being probed and many thousands of leaks and decay diagnosed, MDC partnered with the University of Auckland and dozens of experts, and produced a range of solutions that could be customised to almost any ‘leaky home’.

    Homes built without the ‘Belts and Braces’ could have them installed where they were needed one wall at a time.

    • Post-treatment to kill existing decay and treat against future decay without pulling the cladding off,
    • Drying skirts instead of a cavity,
    • Upgrading Taylor type gutters,
    • Window flashings to direct window leaks out from the framing,
    • Window eyebrows to protect the top of windows where the eaves are inadequate,
    • Systems for installing flashings and sealing penetrations.

    Underpinning these tools are the Mdu Probe system which finds leaks and decay, then monitors the success of the repairs and the emergence of any future leaks.

    The great majority of plaster clad houses can be made safe, dry and durable meaning that recladding is not required and much of the value loss caused by the ‘plaster home stigma’ can be reversed.

  • 2020

    Expiry of Durability Period Opens Up Repairs Without Building Consnet

    The Building Code requires that if elements of a building fail within the expected durability time, then a Building Consent is normally required for repairs.  The stated durability for cladding is 15 years and most houses built in the leaky home era are now older than this.

    This now gives homes owners more latitude to repair their houses to make them safer and more durable,  without going through an expensive and time-consuming building consent process.

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.