Treated to H3.2, H4, H5, H6 - 150mm to 600mm sed Diameter.

North Sawn Timber Ltd specialises in the production of high density pine, ground treated construction poles for use in foundations, driven piles, retaining walls or structures and H6 Marine poles and whalers. The design of the pole shall generally take into account, as appropriate, the limit states of stability strength, serviceability, durability and other requirements of AN/NZS 4676:2000. North Sawn Treatment Ltd is our own in house specialist treatment service provider with the most modern plants in the country and we treat up to 15,000 cubic meter of timber per month at our Ruakaka, Marsden Point site.


North Sawn Timber Ltds poles are shaver peeled to produce an even smooth finish but are still left with the trees natural taper for maximum structural strength then kiln dried on site. These Poles are used in situations where specified strength is required, for instance, H5 poles are widely used in New Zealand for Retaining Walls, Utility Pole and House Foundation Piles. These are generally treated to Hazard class H5 for critical end use including use in fresh water and Marina Poles are always treated H6.


With hazard class specifications, the nature of the biodegradation risk (decay, wood-boring insects or termites) is first determined from the wood exposure conditions (e.g. indoors, protected from the weather, outdoors, random or continuous wetting, in ground contact) and the preservative retention and penetration into the wood are varied to reduce the risk of biodegradation and product end life expectancy to an acceptable level. Treatment Hazard classes identify the end used for a treated product according to NZ standards. These take into account the risk exposure caused by insect and decay fungus for the end used application of the timber.


In New Zealand, roundwood (posts and poles), sawn lumber, and plywood are treated to the following six hazard class levels.

  • H3.2 – For exposed exterior situations and more critical end uses. CCA is the main preservative used.
  • H4 – Sawn lumber, roundwood and plywood used in ground contact in non-structural situations. CCA are used BY NSL for wood in this category.
  • H5 – Sawn lumber, roundwood and plywood used in ground contact with extreme decay hazard or structural end-use requireing greater protection – mainly for house foundation piles and transmission poles. CCA are approved for this use.
    Preservative retentions are 33% higher than those of Hazard Class H4.
  • H6 CCA only – Sawn lumber and roundwood used in a marine environment. The main New Zealand pine commodity treated is marine piles.

Preservative treatment requirements are generally equivalent to or exceed those of other countries which have formal wood preservation standards.



Performance requirement

Sizing of Poles is be specified by nominal length, and minimum small end diameter.
The design strength in bending (fb) for the poles and posts shall be 38MPa. ( 52 MPa Characteristic per NZS 3603:1993)
Round Construction Piles and Poles meet the H5 treatment requirement specified in NZS3605:2001.
Treatment is undertaken in accordance with NZS3640: 2003. Timber Treatment Hazard Classes. No limited guarantee or warranty exists on any timber products drilled,rebated,end cut or any other action tended to the product that breaks the treatment envelope after treatment has been completed.
North Sawn Timber Ltd operates an independently verified Production Quality Assurance Plan through AsureQuality.
Timber treatment meets the requirements for specified Hazard Classes as defined in NZS3640: 2003.
All NSL poles have characteristic stresses and modulus of elasticity that conforms to the High Density Category for round timbers as defined in NZS3603:1993. All Logs are sourced from renewable plantation forests in the Northern region of New Zealand



Service lifespan of North Sawn Timber Poles is no less than that required by each treatment hazard class performance levels as defined in NZS3640: 2003 therefor it is imperative that engineers,designers,installers all design,speciffy and instal the correct hazard class required by the NZ building code.ie H3.2 no in ground exposure or water submersion,H4 suitable for ground contact but non structuaral , H5 for all structural components and H6 for all Marine applications,
NOTE H6 preservative chemical has no guarantee from North Sawn Timber Ltd or our chemical supply companies due to the fact that Toredo Worm is present in salt water. The Toredo Worm will bore into H6 treated timber and while the worm dies the boring holes open up the timber and can expose areas of the timber to seawater ingress leading to rot.
While we are unable to guarantee the H6, what we do have is fully compliant operation backed by full independent third party auditing via AsureQuality. We believe this treatment auditing program offers the highest level of compliance in New Zealand.
Treatment plant capability operating systems and compliance programes deliver fully compliant H6 treatment. The NSL CCA plant is the most modern plant in the country and out performs most other plants in the country due to the fact it achieves target pressure and it does this in a very short time. Further to this control of the treatment cycle is very important and with a new plant we are able to manage our treatment to ensure compliance at all times. The chemical retention safety margin is also important to ensure complete compliance as if you operate a high safety margin it ensures that any variation on chemical uptake is still compliant, within reason. NSL have a safety margin of 33%.
Timber selection is also vital as H6 treatment requires a minimum of 40mm penetration on all faces with H6 chemical retention levels to achieve compliance. Timber must be cut to order for H6 products to ensure that there is sufficient sapwood on all faces to ensure compliance. NST has specific cut plans when sawing timber destined for H6 treatment.

New Zealand pine is not a naturally durable species and its use in New Zealand for structural purposes has gone hand-in-hand with the development of an efficient wood preservation industry.
Unlike many traditional softwoods the sapwood of New Zealand pine is very permeable to wood preservatives, particularly in the radial direction.
Complete sapwood penetration is always achievable, resulting in very extensive service lives for such commodities as electric power or telecommunications transmission poles, marina poles, ground retention etc.
Total sapwood penetration with preservatives is rarely achieved with other softwood species.

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