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)
Buyers Guide (25)
Information on alternatives to pine and their structural properties.
Information on Douglas-fir as an alternative solution
Visit the Species Index on the website.
NZ Wood is a promotional programme and information provider for the wood industry in New Zealand. As such, we do not sell any product or act as a broker or intermediary. We do however have a vendors’ database on the NZ Wood resources site which includes contact and product details for a wide range of wood and construction products throughout New Zealand.
Please refer to the NZ Wood Suppliers Database
NZ Wood is a promotional programme and information provider for the wood industry in New Zealand. As such, we do not sell any product or act as a broker or intermediary either within New Zealand or internationally.
Our comprehensive vendors’ database does give details however of New Zealand producers who would be delighted to talk to you about your purchase requirements.
Please refer to the NZ Wood Suppliers Database
Hardwood is not necessarily a harder material (more dense) and a softwood is not necessarily a softer material (less dense).
Different types of construction projects call for different kinds of timber, both hardwood and softwood are used for everything from structural to decorative.
Softwood and hardwood are distinguished botanically in terms of their reproduction, not by their end use or appearance. All trees reproduce by producing seeds, but the seed structure varies.
In general, hardwood comes from a deciduous tree which loses its leaves annually and softwood comes from a conifer, which usually remains evergreen. Hardwoods tend to be slower growing, and are therefore usually more dense.
Softwood trees are known as a gymnosperm. Gymnosperms reproduce by forming cones which emit pollen to be spread by the wind to other trees. Pollinated trees form naked seeds which are dropped to the ground or borne on the wind so that new trees can grow elsewhere. Some examples of softwood include pine, redwood, douglas-fir, cypresses and larch. (more information visit our species section)
A hardwood is an angiosperm, a plant that produces seeds with some sort of covering such as a shell or a fruit. Angiosperms usually form flowers to reproduce. Birds and insects attracted to the flowers carry the pollen to other trees and when fertilized the trees form fruits or nuts and seeds. Hardwoods include eucalypts, beech and blackwood.
The hardwood/softwood terminology does make some sense. Evergreens do tend to be less dense than deciduous trees, and therefore easier to cut, while most hardwoods tend to be more dense, and therefore sturdier. In practical terms, this denseness also means that the wood will split if you pound a nail into it. Thus you need to drill screw or bolt holes to fasten hardwood together. But structural lumber is soft and light, accepts nails easily without splitting and thus is great for general construction.
Limited quantities of native or indigenous timber are still harvested and milled in New Zealand, but this makes up less than 0.1% of New Zealand’s timber production.
Is it acceptable to use untreated macrocarpa for fence palings, and what ground clearance is recommended?
The How-to-build guide on fencing compiled by BRANZ (based on using H3.2 treated radiata) recommends a minimum ground clearance of 50 mm.
With untreated wood the concern is that rain splash will put dirt onto the bottom of the paling, causing it to accumulate on the horizontal bottom edge. This then pushes the decay hazard above the H3.2 level. If there is fresh earth next to the palings then the dirt can be splashed higher than 50mm. If there is grass or paving then there might be no dirt splashed up at all.
Depending upon the application, therefore, it might be advisable to have a greater ground clearance than the 50mm recommended for H3.2 treated radiata.
Fencing is not a structural situation so compliance with the Building Code is generally not required if the completed structure is under 1.8mtrs high. It will also depend on what sort of a fence you are building, so check with your local council before you undertake any construction just to be sure.
See Macrocarpa on the species sectoin
More about Hazard classes
Macrocarpa is suitable for decking and does not need to be treated. Its natural durability can be sufficient for this purpose.
However, its durability is unreliable in moderate-high decay hazard situations, and occasional failures may occur within 10-15 years. Therefore it is not recommended in-ground, such as for posts and piles.
See Macrocarpa on the species section.
See the how-to guide for information on building a deck.
Kiln dried timber usually has drier and wetter pieces that will slowly adjust to whatever equilibrium moisture content is appropriate to the situation they are in.
To acclimatise the timber ‘in situ’ prior to installation, the flooring is stacked with fillets (narrow strips of wood) between each layer. It will have been delivered block stacked, i.e. without fillets.
If the house is under construction then there is little point in doing this because the ambient conditions during construction will not be those when the house is complete and occupied. Some change is unavoidable as the flooring equilibrates to the final conditions.
If, however, the flooring is to be used for an extension to an existing house then there is merit in fillet stacking it for two or three weeks to “acclimatise” (or equilibrate) and this will keep any subsequent shrinkage to a minimum.
More on moisture measurement
More on the timber drying process (focuses on pine but is applicable to other species)
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. They are set out in the Hazard Classes .pdf. More detail about the actual hazards is provided in the found on the Hazards page of the website.
For board and batten cladding, cedar is excellent although it is the most expensive. Imported cedar is always completely free of knots.
The second choice is heart macrocarpa. It is unlikely that there would be any or much sapwood in macrocarpa but sap macrocarpa is not durable. Knots in macrocarpa have an undesirable habit of checking but for vertical board and batten cladding that is not a problem because it will be backed with a building wrap.
Douglas fir should be durable enough for this application but there are doubts, especially if there is some sapwood on the boards.
For that use the heartwood of western red cedar, or macrocarpa would be suitable. Locally grown western red cedar is likely to be knotty and slightly less durable than imported western red cedar. Imported western red cedar has been available in clears and knotty grades but the latter sometimes include bark encased knots which are likely to come loose in service. Douglas fir is less durable, somewhat unreliable, although it has been used for external sheathing.
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.
Wood is fast and flexible
- Timber provides for flexibility of design, and allows modifications and tweaks to layout during the construction process. Factory pre-fabricated and pre-cut steel frames do not.
- Builders are familiar with using wood, and usually prefer it. Builders report frame construction times of two to two and a half times longer for steel frames.
- Steel frames, however, have the advantage of being able to be constructed in wet weather, and do not require the drying time of wood frames. Wood moves as it dries out.
- Wood is a lower cost raw material than steel.
Snug and sound – Thermal performance
- Wood is 400 times better as a thermal insulator than steel and 14 times better than concrete.
- In solid form, wood also has significant thermal mass properties, retaining heat from the day and releasing it at night.
- Wood also acts as a humidity regulator, absorbing moisture when humid and desorbing moisture when the air is dry.
- Read more about the thermal performance of wood
Wood doesn’t rust
- All building materials used for the structure of houses in New Zealand are required to have a minimum service life of 50 years to comply with the building code.
- Wood, used appropriately in accordance with building standards, will usually far exceed this.
- The mutual enemy of both wood and steel is moisture. Ingress of moisture into wall cavities should be minimised and the design should ensure that any moisture that does enter from leaks or condensation can drain and dry.
- Although steel is normally galvanised to protect it from corrosion, steel frames are susceptible to rust where the surface coating is cut, scratched or penetrated, and from edges that have been cut.
- Wood treated with the appropriate level of preservative, and properly maintained, can last in service for a hundred years or more.
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.
The main issues are:
- Colour – fading, discolouration, ultraviolet effects, mould growth
New Zealand grown species that could be considered are:
- Radiata. Must be treated to H3 or H4. CCA is the only commonly available treatment that will achieve sufficient durability. An alternative to CCA would be ACQ or Cu-azole treatment but may be hard to find. (Timber treatment companies such as Osmose or Arch should be able to advise on availability.)
- Macrocarpa. Does not need treating, otherwise similar to radiata. Note: macrocarpa can be unreliable where it is fully exposed to the weather, i.e., a few pieces are likely to fail or need replacement within the 15-year minimum durability requirement.
- Eucalypts. These are mostly durable hardwoods. The Eastern Blue Gum group: (E saligna and E. botryoides) and the Stringybark group: (E. muelleriana, E. globoidea, E. eugenoides, E. microcorys, E. pilularis) are most suitable for decking.
- The heartwood of all the blue gum and stringybark species are durable in ground contact, lasting 15 to 25 years in ground contact and up to 40 years out of ground contact, giving an equivalent durability of H3.2.
Permanently shaded areas will become slippery so regular maintenance (waterblasting) is needed. Decking is usually grooved to reduce slipperiness. A surface coating of high built glassfibre-reinforced epoxy coating will overcome most of these problems. Screw fixing may be preferable to nail fixing although decking nails are resistant to popping. All timber is porous so will allow mould to penetrate and cause discolouration.
Wall linings for indoor pools
Durability is less of an issue with indoor pool wall linings. There is no danger to the wood from chlorinated water. It does not damage the wood and acts as a mild preservative. There will be discolouration though, as with any wood if it gets splashed.
Commonly available timber options would include pinus radiata, Douglas fir and macrocarpa. New Zealand-grown eucalypts could also be considered, or indigenous timber such as beech where a high end finish is desired.
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 use of plywood thickness would depend on the spacing of the support structure.
The use of plywood for guttering would normally be specific to the design as it depends on the size of the gutter, the support spacing and what depth of water is expected to be flowing in the gutter.
e.g. typically in a plywood low pitch roofing situation, 15mm F8 plywood could work with supports at 600c/c or for a plywood deck you could use 19mm F8 plywood with supports at 600c/c.
It is hard to gauge the size of the timber that is needed without knowing the full extent of your idea, but NZ Wood has a general guideline for building a light structured lean-to roof (pergola)
First we would suggest that you check with your local council to see if you need building consent (especially if you are thinking of attaching it to your house). They are able to give you a quick rundown on the building code and if you need to apply for building consent.
To give you an idea of what timber and materials are recommended for use, view the how-to-build-guide for building a free-standing pergola which gives you an idea of what timber sizings, treatments and materials are recommended for use.
The building code specifies standards for slip resistance of pedestrian access routes. 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 the basic information in a comprehensive format.
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 will require 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.
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.