Engineered Wood & Durability – Key Vocabulary

Essential vocabulary covering engineered wood products, moisture behavior, preservative treatments, durability classes, detailing, and corrosion-resistant connections.

Hygroscopic behavior

The ability of wood to absorb or desorb water vapor until it reaches equilibrium with surrounding air.

Equilibrium Moisture Content (EMC)

Moisture level at which wood is neither gaining nor losing water to the environment.

Oven-drying method

Lab procedure that determines wood moisture content by weighing a sample before and after drying at 103 ± 2 °C.

Electrical-resistance meter

Hand-held device that estimates wood moisture using the change in electrical resistance between two probes.

Swelling and shrinking

Dimensional changes that occur as wood gains (swells) or loses (shrinks) moisture below the fiber-saturation point.

Sawn timber

Solid wood cut directly from the log; size limited by tree diameter (~450 mm for radiata pine).

Softwood

Wood from coniferous species (e.g., radiata pine, Douglas-fir) widely used in NZ construction.

Engineered wood product

Wood composite manufactured by bonding smaller pieces or fibers to achieve larger sizes, better quality, or specific properties.

Glued-Laminated Timber (Glulam)

Engineered wood beam formed by gluing dimensional laminations; can be homogeneous or non-homogeneous lay-up.

Finger jointing

End-to-end joining technique using interlocking 'fingers' to create longer, defect-free lumber pieces.

Laminated Veneer Lumber (LVL)

Product of parallel-laminated veneers bonded with adhesive, giving high strength in one direction.

Oriented Strand Board (OSB)

Panel made of aligned wood strands compressed and bonded with resin, often described as ‘cheese-grater’ flakes.

Plywood

Panel of cross-laminated rotary-peeled veneers, offering balanced strength and stability.

Wood I-beam / I-joist

Composite member with LVL or sawn flanges and OSB/plywood web, optimized for high moment of inertia and long spans.

Pole / roundwood

Structural log used largely un-machined; bark removed and often preservative-treated for in-ground use.

Cross-Laminated Timber (CLT)

Large, solid-wood panel built from perpendicular layers of lumber, enabling prefabricated walls, floors, and roofs.

Prefabrication

Factory production of building elements (e.g., CLT panels) for rapid, low-waste on-site assembly.

CNC machining

Computer-controlled routing or drilling that cuts openings in CLT or other panels with high precision.

Second moment of area

Geometric property (moment of inertia) dictating a member’s bending stiffness; increased by material at flanges.

End grain

Wood surface perpendicular to fibers; absorbs moisture fastest and is most vulnerable to decay.

Sacrificial layer / rain screen

Removable outer cladding that protects primary structural timber from weathering and UV.

Hazard class H1.2

NZ classification for internal framing; boron-treated to resist insects/fungi (pink-pigmented timber).

Boron treatment

Diffusible preservative (boric acid/borax) providing low-hazard protection; indicated by pink pigment.

Hazard class H2

Australian internal framing requirement offering added termite protection compared with H1.2.

Chromated Copper Arsenate (CCA)

Copper-based preservative (green tint) for H3.2–H6 uses; effective but contains carcinogenic arsenic.

Micronized Copper Quaternary (MCQ)

Alternative copper preservative with finely ground particles and reduced environmental toxicity.

Alkaline Copper Quaternary (ACQ)

Arsenic-free copper preservative for exterior timber applications.

Sea spray zone

Environments within ~500 m of coast where salt accelerates corrosion; calls for stainless-steel fasteners.

Stainless-steel fastener

Corrosion-resistant connector mandatory for exposed, coastal, or highly treated timber situations.

Hot-dipped galvanized fastener

Steel fastener coated with thick zinc layer; suitable for most exterior but non-marine exposures.

Zinc-coated (electro-galv) fastener

Light zinc-plated fastener appropriate only for interior, sheltered timber joints.

Leaky-building syndrome

1990s NZ construction crisis where poorly detailed stucco façades allowed water ingress and timber rot.

NZ Building Code B2

Regulation setting 50-year durability requirement for structural building materials.

NZS 3603

New Zealand Standard specifying design and durability provisions for timber structures.

UV degradation

Surface weathering caused by ultraviolet light, producing silver-grey colour and fine checks.

Teredo worm

Marine borer (shipworm) capable of attacking submerged timber, necessitating higher hazard classes.

Termite

Wood-destroying insect prevalent in Australia; drives higher preservative requirements (H2+).

Fungi (decay)

Organisms that digest moist wood, leading to strength loss when moisture content exceeds ~20 %.},{

Moisture meter

Device (pin-type or pin-less) used on-site to assess timber moisture for decay risk or compliance.

Checks and splits

Cracks from differential shrinkage; often initiate at end grain or around fasteners, accelerating decay.

Sacrificial cladding

Non-structural covering intended to weather and be replaced, preserving the main load-bearing timber.

Ventilation path

Intentional air gap behind cladding or rain screen promoting drying of timber elements.