Welcome to the NZ Wood Frequently Asked Questions
- Buyers Guide (25)
- Environmental (7)
- Forestry (9)
- Pine (9)
- Processed Wood (33)
- Using Wood (47)
- NZ Wood (3)
Through good silvicultural management, New Zealand pine logs come in a range of qualities capable of yielding lumber grades to meet almost any requirement.
For detailed information about NZ Pine (Radiata Pine) quality and the conversion process go to Log Quality, Conversion and Grading page on the website.
Untreated macrocarpa, Lawson Cypress, Lusitanian Cypress or Larch are possible options.
To achieve an “acceptable solution” within an enclosed frame H3.1 treated radiata needs to be substituted with either:
- Structural grade untreated larch, or
- Untreated heartwood from the cypress species (or H1.2 treated sapwood). Macrocarpa is the most likely source, but Lawson cypress may be available although unlikely to be in large supply. (The heartwood is easy to identify, and available, if you find a supplier of the species.)
For both of these, because they are specialist species, they could be hard to source for structural purposes ie. MSG or VSG 8 or better. Very few producers will go through the “verification” steps for small scale volumes.
If MSG 6 is sufficient then visually graded “number one frame” will be an acceptable alternative. (Unverified “number one frame” is deemed MSG 6 and it can be used in place of MSG 8 but will require larger dimensions to give equivalent strength)
That leaves “alternative solutions”:
- Research would support H1.2 boron treatment as being suitable for enclosed frames in any situation and some Building Consent Authorities (BCAs) will approve H1.2 Douglas-fir in place of H3.1 Radiata.
If it is an outdoors or exposed structural application eg. posts where 50-year durability is mandated, then the building standard NZS 3602 does not designate any commonly available untreated wood as an “acceptable solution”.
NZS 3602 allows untreated heartwood from redwood, western red cedar, cypress species and New Zealand beech for outdoor use in stairs, decking, handrails where a 15-year durability is required.
(Note: because of the risk of leaching, H1.2 boron should not be used in exposed areas unless it is primed and three-coat painted.)
For more information on treated timber and building legislation visit the Treatment and Durability section of the website.
Look at the table of alternatives to pine and their structural properties.
1.CCA treated timber has been shown in some studies to leach low levels of chemicals into the soil immediately surrounding the treated timber. Soil tested within 25 mm of the treated timber sometimes slightly exceeded advisable safety levels for arable soil.
Soil tested further than 25 mm from the treated timber showed no significantly raised arsenic levels compared to other NZ soil. (Note, background levels of arsenic in New Zealand soil are between five and nine parts per million approximately or 5-9mg/kg.)
Uptake of these chemicals by fruit and vegetables has been shown to be minimal and is within accepted international food safety thresholds.
If you are particularly concerned, it is suggested you plant no closer than 35cm to the timber edge or place a plastic or polythene barrier between vegetable garden soil and the CCA-treated timber edging.
2.Do not use LOSP treated timber – it is not rated durable for in-ground applications.
3.You could instead use untreated timber from a species with higher natural durability like macrocarpa or some eucalyptus species, however if left in contact with the ground the timber will eventually rot.
Common options for cladding include:
- Radiata pine
For radiata pine weatherboards that are clear finished or unpainted, the minimum treatment is H3.2. Painted, the minimum treatment level is H3.1.
Weatherboard cladding made from radiata pine is widely used in New Zealand, including areas with demanding climatic conditions. Because of the presence of spiral grain, the juvenile wood of New Zealand pine should not be used where stability is vital to performance. Dimensional performance can be increased by use of finger-jointing, and/or lamination. Such highly processed laminated, finger-jointed clear products are used widely in Japan where a maximum stability is required.
This is discussed in the FAQ section
- Leyland cypress
Leyland cypress is a hybrid of macrocarpa and should be even more durable. It is certainly very stable, and should be even better for cladding.
- Western red cedar
Western Red Cedar is a species commonly used in New Zealand for natural looking claddings. This is mostly imported from Canada. The New Zealand grown timber is usually regarded as inferior to the old growth timber from British Columbia, which is very stable and durable. As with all timber cladding, it is highly recommended that cedar has a protective coating of either stain or paint.
For more on wood choice, the Substrates page on the website may be of help.
In terms of finishes for the timber cladding, please see the Exterior Finishes section on the website.
It is advisable to avoid dark colours for most wood cladding. The finishes section of the website provides some guidance on light reflectance and heat generation.
What is the availability and suitability of indigenous or NZ grown large beams of timber for outdoor use?
The question relates to timber of cross section 200mm x 250mm for a large outdoor architectural feature. It needs to stay straight, not split or warp, and to silver off without the need for staining and other maintenance.
The size of the beams and availability could be difficult. Indigenous timbers which might have the durability (beech, totara) are not likely to be available in big enough sizes or big enough quantities. The size also means the timber could not be dried and that makes stability a problem.
A good solution would be macrocarpa or Douglas-fir heartwood glulam as the lamination will overcome any problems with knots and it will be properly dried before it is glued.
Look in our Suppliers database to search for a supplier near you.
With moderately durable species like the cypresses the degree of exposure is important. If the wood is wet frequently and remains damp for long periods the chances of decay within 50 years are relatively high.
Verandah posts and beams may be wet occasionally when there is rain but the surfaces exposed to wetting are usually vertical, are well ventilated and clearly visible. Therefore the risk of decay developing is relatively low. There are plenty of examples of old buildings with kauri and rimu verandah structures that are more than 50 years old.
If end grain is exposed to wetting, significant water penetration is likely. This will increase susceptibility to decay and additional protection, either with some sort of cover or with regular application of a water-repellent coating, would be advisable.
Macrocarpa (Cupressus macrocarpa), has heartwood that is in Australasian durability Class 3 i.e. in testing of ground contact 50 x 50 mm stakes it has been shown to have an average life of 5-15 years. The average life is towards the upper end of this range but a few early failures occurred in the tests. Rimu (Dacrydium cupressinum) and kauri (Agathis australis) heartwoods have the same durability classification.
Away from ground contact but fully exposed to the weather the average life of 50 mm thick cypress heartwood is 15-25 years. This is similar to the durability that could be expected from timber treated to the H3.1 specification with light organic solvent preservatives (LOSP) although there is usually more variability in naturally durable timber than in treated radiata pine sapwood.
Horizontal, upward facing surfaces, end grain and joint areas where water can be trapped are most susceptible to decay. If the surfaces are only partly exposed to the weather, are vertical or steeply sloping, and not end grain, the chances of decay are relatively low and a much longer service life is likely. 100 x 100 mm verandah support posts on steel brackets and with the upper ends protected by an overhanging roof are likely to have a service life several times greater than that of fully exposed 50 mm thick material.
The Building code for slip resistance for pedestrian access routes states that surfaces which provide the direct access route (including where this is a deck) require a slip resistance of 0.4.
The Department of Building and Housing website has an overview regarding slip resistance
The Building Code compliance document D1 outlines the requirements for access routes, and states in Table 2 that timber is OK in dry level conditions, but needs an across-grain profile or sand/grit finish for wet and sloping zones. Algal growth over time would need waterblasting as a maintenance scheme, as per subclause 4 of table 2. Alternatively, unprofiled timber can be used with a fixed weatherproof coarse matting providing slip resistance of 0.4 for the main access route across the deck.
If your beam is going to be used in a situation where appearance is important such as house interiors, halls etc – appearance Grade A should be specified. This calls for a flush, filled and sanded surface.
Appearance Grade B is intended for applications where surface appearance is not so critical and a machine planed finish that may have occasional skips and other minor voids is acceptable.
Glue-laminated timber (glulam) is the name given to large solid wood members manufactured by gluing many smaller pieces together. Glulam is an engineered structural material consisting of a number of graded, kiln dried and selected full length laminations – usually 45 mm thick – bonded with proven adhesives, to form a solid member of practically any length, shape or size.
The main reason for laminating is to produce larger size members than possible in solid sawn timber. There is also an increase in strength. The strength of a single piece of timber is as strong as its weakest point, which is usually the largest knot.In laminating, the weakest point of one piece of timber is bonded to the higher strength of adjoining pieces, thus forming an homogeneous structural component of great efficiency.
Most timber is susceptible, to varying degrees, to biological degradation from various hazards such as heat, moisture and insect attack.
In the context of building products it is reasonable to expect that, subject to normal maintenance, the product will last for a specified number of years.
Therefore timber needs to be treated to prevent degredation.
Visit the following pages on the website:
Glulam is suitable, and should be treated for exterior use (see Glulam Durability)
Treatment options are H3.1 (LOSP) which needs to be painted and maintained, or H3.2 (painting is optional but recommended). The designer needs to ensure that H3 treated timber is not in contact with the ground.
For further information, a local Stratalam supplier (see www.stratalam.co.nz) will be able to help.
Paint suppliers can help with recommended paint systems.
Because glulam is manufactured from selected grade, kiln dried material it is stronger and more stable than a solid timber beam of the same section. The tendency of large section solid timber to twist, split and shrink is greatly minimised in glulam.
A glulam beam can reduce the overall section of members up to 40% compared to unseasoned timber.
The new glulam code AS/NZS 1328 allocated Glulam beams manufacturers in New Zealand radiata pine to three grades – GL8, GL10 and GL12. These figures refer to the stiffness (E) of the beam.
The most common is GL8; some manufacturers are certified to produce GL10 or GL12. Check with your supplier.
All glulam available in New Zealand must be manufactured to comply with the joint Australian and New Zealand standard.
Licensed manufacturers are regularly inspected by the NZ Timber Certification
Board and issued with an individual license number. This certifies that the manufacturer’s production system complies with the detailed requirements of AS/NZS 1328 – Glue Laminated Structural Timber.
Audits are also carried out by Bureau Veritas to ensure compliance and quality control procedures and records are in place.
To ensure you have a quality product check that your supplier has a current license number.
In order to maintain the best condition of manufactured glulam proper storage and handling is important.
Beams should be stacked well clear of the ground and protected from the elements. Stacks of beams should be covered with a weatherproof material ensuring adequate ventilation to prevent condensation building up.
Avoid black polythene, as this will make the beams sweat.
If possible, fillet stack beams to allow air circulation.
The gradings of glulam and solid timber beams are directly comparable. For example GL8 graded glulam has “equivalent or better” structural performance than MSG8 timber.
The average stiffness of both grades is 8 GPa, while the strength (bending, compression etc) values are higher for glulam.
The stress gradings for glulam are directly comparable with solid timber. Verification of this should be provided by you glulam supplier which should demonstrate compliance with necessary building codes.
Laminated veneer lumber (LVL) is a structural product manufactured from thin peeled veneers of wood glued with a durable adhesive with the grain running parallel to the main axis of the member. Panels of LVL are cut into structural members which have high strength and stiffness
LVL is suited to structural applications such as beams, rafters and columns in a wide range of buildings including houses, commercial, industrial and rural structures. Some special LVL has a small number of veneers laid perpendicularly (cross banded).
LVL has a number of advantages over other wood-based materials:
- Small logs can be made into large dimension LVL products.
- Long lengths of LVL are available; up to 12m ex stock from merchants (or 18m by arrangement).
- The wood resource can be optimised by grading and selecting veneer for different parts of an LVL cross section and making a range of products with different properties.
- Structural properties of LVL are very uniform because the randomised layers of thin veneers are pre-graded for stiffness (coefficient of variation for modulus of elasticity less than 5%).
- LVL members have high strength because of the low variability and randomised wood properties in thin layers.
- LVL can be cut and machined with normal woodworking tools.
LVL is often used to complement the use of sawn timber in domestic construction. In commercial or industrial structures it is often used as a wood-based alternative to structural steel or reinforced concrete. Generally LVL becomes attractive when sawn timber is not strong enough to do the job, or long lengths are needed.
New Zealand uses strength gradings such as MSG (machine stress grade) or VSG (visual/verified stress grade)
The Lumber and Grades page on the website has a good description of the grades and methods of grading.
Six Hazard classes are used to describe the service exposure conditions in relation to biological hazards that could cause degradation of wood. More information is available on the website
The Building Act 2004 sets out the legislation on building standards and procedures. The Building legislation and regulations page of the website has detailed information on this.
Six Hazard classes are used to describe the service exposure conditions in relation to the biological hazard. More detail about the actual hazards is provided in the Hazards that can affect wood section of our website
Are there special timber treatment requirements for NZ Radiata timber in tropical conditions, especially insect attack?
Use CCA treated timber for termite protection, H2 is for framing timber, H3 (not H3.2) for above ground exterior and H4 or H5 for ground contact.
Australian standards are usually applied with regards to dealing with termites in the Pacific Islands.
AS 1604.1 for sawn and round timber, AS/NZS 1604.2 – AS/NZS 1604.5 for reconstituted wood products, plywood, LVL and glue laminated products.
These standards would meet or exceed likely requirements in tropical areas where termites are a hazard.
Standards New Zealand: Timber Treatment –
New Zealand uses strength gradings such as MSG (machine stress grade) or VSG (visual/verified stress grade)
The Lumber and Grades page on the website has a good description of the grades and methods of grading.
New Zealand uses strength gradings such as MSG (machine stress grade) or VSG (visual/verified stress grade) whereas Australia uses MGP (machine graded pine). The MGP grades are slightly different to the MSG grades and are not directly comparable.
New Zealand specifiers should be specifying MSG or VSG grades for New Zealand. Australian grades would have to be dealt with as an alternative solution under the New Zealand Building Code as far as the consenting authority is concerned.
There are chemical reagent tests for boron, copper and tin compounds which, when sprayed on freshly cut surfaces, will tell you whether these elements are present but will not indicate what level of treatment has been achieved. This can only be done with chemical analysis (destructive) of wood samples.
In the case of the question asked, the wood had a green tinge, suggesting it is most likely to have been treated to the H3 or more recent H3.2 specification with copper-chrome-arsenic (CCA) preservative.
There are testing laboratories that can test small samples of the wood. One is operated by Scion – the former Forest Research Institute in Rotorua.
Contact Katrina Martin in the Veritec Analytical laboratory.
email@example.com or DDI (07) 343 5598.
These days most H1.2 treatments are with boron salts. These are very low toxicity preservatives and should pose few problems when used for indoor furniture, although it would be a good idea to ensure there is either a paint or other surface finish on the furniture so that there is no direct skin contact with the treatment.
H3.1 treatments are usually organic solvent treatments (eg. LOSP). These can cause some dermatitis-like problems when freshly treated timber is handled, particularly if a lot of residual solvent remains. They also have a fairly pungent aromatic smell which may take a while to dissipate from the treated timber. Again, painting of the timber would be recommended once all the solvent has evaporated.
H1.2 boron treatment would be the preferable option.
Untreated kiln dried pine should not be regarded as equivalent to H1.1 treated framing.
H1.1 timber specification covers additional protection against insect attack and H1.2 should be used if H1.1 timber is not available.
NZS 3602:2003 does specify a number of instances where kiln dried untreated framing can be used as an alternative to H1.1, but untreated wood should not be used unless specifically allowed.
The understanding is though, that the standards will be changing very soon, and kiln dried untreated timber will be excluded from most of the areas that it is currently permitted in.
It is also likely that the H1.1 specification will also be removed completely and that timber treated to the H1.2 specification will be the minimum requirement for almost all radiate pine framed houses.
More information on Wood Preservation and the Hazard classes
Also read What is a Hazard Class?
The piles are expected to be permanently below ground level after construction. Groundwater level is expected to be not far below the tops of the piles.
Wooden piles in this context should give a 100+ year service life. Untreated wood that is permanently below groundwater level will not decay so treated wood certainly won’t either.
The large size of the piles means that there is much more preservative chemical present than in the 50x50mm stakes on which decay resistance is normally evaluated. This means that the above-groundwater portion will have a longer life than is assigned to H5 timber which will be longer than H4 treated timber in the same situation.
An architect had an issue with raised grain on exterior facings. The facings had been used as part of an expensive reclad on a previously leaky home. While they were weathertight, the owner was unhappy with their appearance and demanded that the problem be rectified.
Raised grain is a machining fault caused by springback of compressed wood when its moisture content increases. The compression can be caused by blunt or improperly jointed planing knives.
To resolve it is best to leave the problem areas until after summer if possible, allowing the heat and summer humidity to allow full stress relief before sanding and then repainting.
Refer to the pages on Exterior Finishes on the NZ Wood website
The dust from MDF is no more harmful than ordinary wood sawdust. When working with any dusty situation it is a good idea to minimise your exposure to it by having good extraction and/or a dust mask as lungs don’t like dust.
If the MDF is sourced from New Zealand suppliers then formaldehyde emissions from a whole panel of raw board will be well below the World Health Organisation (WHO) guidelines for within a house.
Formaldehyde is a naturally occurring substance found in all kinds of living organisms including wood. The body is quite capable of metabolizing it and it does not bioaccumulate.
Formaldehyde is also produced by wood fires, cars, lawn mowers, permanent press drapes, and some other fittings. It is only at really elevated levels found in manufacturing operations that it causes stinging of the eyes and nose. These are levels 10 times or more above the WHO guidelines for within a house.
If you are still worried, paint the cut surface as this significantly reduces the already minimal emissions.
Timber is the name given to wood that has been prepared for the purpose of building or carpentry. Preparation includes the drying and sometimes treatment of this wood.
There are a few methods of drying wood in New Zealand including:
- Ambient temperature drying – air drying and forced air drying.
- Low temperature dryers (up to 60C, usually 40-50C) – heated forced-air dryers and low temperature kilns including most heat pump dryers (dehumidifiers).
- Conventional kilns (usually temperatures of 60-80C for New Zealand pine).
- Accelerated conventional-temperature kilns operating at temperatures of 80-100C.
- High temperature kilns (temperatures above 100C, usually 120C or higher).
- Vacuum drying, which is new to New Zealand, offers the potential of rapid drying and minimising discoloration of high quality lumber.
“Kiln drying is an industrial unit operation used to accelerate the drying of wood. A wood drying kiln is an enclosed space where air speed, temperature and humidity are controlled. Natural air-dying of wood can take weeks, while a wood drying kiln can complete the process in less than a day”¹
The benefit of kiln drying the timber is that it is dried in a controlled environment, has rigorous testing, and is extremely quick giving a higher quality end product. Bugs and insects are also killed during the drying process. Therefore it can be more cost effective and less likely to have distortion, staining or drying stresses (i.e. warping or bowing).
Any softwood needs to be treated for use as decking except macrocarpa heartwood. Its natural durability can be sufficient for this purpose (although its durability is unreliable in moderate-high decay hazard situations, and occasional failures may occur within 10-15 years).
Most hardwood is naturally durable and resists all kinds of wear and tear. Locally grown eucalypts can be suitable for decking.
The Decking How-to-build guide suggests treated Radiata Pine.