NZ Standards Approve Changes That Let Houses Rot
Standards New Zealand approved the reductions in timber treatment levels, which allowed leaky homes to decay, multiplying the damage and repair costs many times.
In this article, you can trace the history of the loss of timber treatment. and download your own copy of the NZ Standards that were supposed to protect us.
Houses here were required to be built using timber with a high level of boron treatment until the late 1980s. Then a change in the treatment categories to harmonise with Australia’s system started a downwards slide until by 1992, the equivalent of fly spray was considered satisfactory. Once this was accepted, it was only a small move down to accept zero treatment in 1998.
Access to some NZ Standards is now free and the MBIE has also sponsored access to view and print a single downloadable PDF copy of many NZ Standards at no charge.
We encourage you to download the actual Standards and trace the history of changes that allowed the Leaky Homes Scandal to start and then explode out of control before the Standards finally tightened up again in 2003.
1952 - 1986 Framing Timber Commodity Specification C8
You can download the full Commodity Specification C8 from Timber Preservation Authority Amendment 3 here.
This is the treatment requirement set by the Timber Preservation Authority and used for framing timber up to the late 1980s.
Note boron minimum retention was 3.2kg/m3. This was originally 4.8kg/m3 but reduced to 3.2kg/m3 in 1975 after better production methods gave more consistent treatment.
A minimum of 0.1% Boric acid equivalent was also required at the core of any sapwood. Both requirements had to be met.
1986 - 1992 Change to Australian Hazard Classifications - Hazard Class H1
The change of classification system was driven because NZ wanted to sell timber to Australia, so we needed to harmonise our systems with theirs.
1986 Timber Preservation Authority – H1 Description
This describes where the newly categorised H1 timber could be used – adequately ventilated and continuously protected from the weather and protected by a roof, external walls or well maintained three-coat paint system.
Our C8 classification became H1, although C8 should have been split into H1 - Insect Hazard only and H2 - Low Decay and Termite Hazard.
The amount of boron treatment in the wood still had to conform to two requirements - the weight of boron retained, and the % of boric acid equivalent (BAE) at the core of the timber and for H1, that was still unchanged from our old C8 classification.
1986 Timber Preservation Authority – H1 Boron Treatment Retention
This shows that at this stage, H1 still required minimum boron retention of 3.2kg/m3 so in practice, there was no difference to the old C8 Specification and the timber was still well treated.
NZMP 3640: 1988 Specification of the minimum requirements of the NZ Timber Preservation Council
This publication sets out specifications for the protection of timber from attack by insects, decay, or marine borers. It provides guidance in the form and composition of the preservative, the care of treated timber and recommendations as to use.
Download this your copy
here;
The standard states that:
- H1 is for timber adequately ventilated and continuously protected from the weather, external walls or a roof. If this had to be protected by an external wall, then it can’t be part of an external wall?
- H2 is timber which because of intermittent wetting, may be exposed to termites or for low decay hazard. This would be the specification most applicable to external walls, where they may get wet and therefore may decay - but we never had it available.
Note that although H2 was mentioned, there was no specification for making H2 in 1988. Just H1 and the higher treatments H3 -H6.
Section 9.7.1.2.2 - H1 boron now specified at 0.1% BAE core retention for softwoods (the specified loading of 3.2kg/m3 is gone and in practice, the overall boron content was allowed to drop massively).
H1 ‘wet frame’ 0.1% boron has since proven to be inadequately treated to protect against major or persistent leaks. As houses age, these leaks are now presenting as serious decay.
We don’t believe that there was any publicity or education given to builders and builder’s merchants advising that H1 made under the new standard had far less treatment and was less durable.
NZMP 3640: 1992 Specification of the minimum requirements of the NZ Timber Preservation Council Inc.
New Zealand Timber Preservation Council performance specifications for the protection of timber from attack of insects, decay and marine borers. Provides guidance in the form and composition of preservatives, the care of treated timber and recommendations as to use. Proof of compliance with the requirements of NZMP 3640 is deemed to satisfy the performance requirements of the New Zealand Building Code.
Download your copy here
The new Standard permitted timber mills to produce H1 branded timber, treated only for insect protection using Permethrin (the same active ingredient as in a can of fly spray). No protection against decay and this rotted just as fast as untreated timber.
A treatment specification for H2 was provided and could be made, but due to unresolved issues with export to Australia, it was forbidden to brand any timber as H2 for the NZ market. So you couldn’t buy it. If you wanted something better than H1, you needed to order H3.
Was the industry aware that H1 may now have absolutely no decay resistance whatsoever?
NZMP 3640: 1992A1 Specification of the minimum requirements of the NZ Timber Preservation Council :Amendment 1
Amendment to the above – no significant change to H1 etc
Download your copy here.
NZS 3640: 2003 Chemical preservation of round and sawn timber
Sets out requirements for the preservative treatment and identification of timber to provide protection from decay and insect attack including marine borers in all likely exposure conditions throughout New Zealand, based on six hazard classes that are described in this Standard.
Download your copy here.
Returns to at least some boron treatment in framing timber with H1 being split into H1.1 (always dry) and H1.2 (risk of moisture content conducive to decay).
H1.1 is no longer made.
H2 now specified as being for Australia only.
Is H1.2 fit for purpose?
Well, the 1952 Boron Enquiry determined that controlling all timber destroying pests required around 3 x the boron treatment that H1.2 contains. In our view, this makes it just OK. Because boron is water-soluble, any sustained leaks will leach out the boron relatively quickly to the point where decay can start.
NZS 3640: 2003A5 Chemical preservation of round and sawn timber
This is the latest Amendment to NZS 3640 however there have been five since the standard was released in 2003.
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Standards New Zealand,
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MP3640,
Untreated Timber,
H1 Treated Timber,
Rotting Timber