Timber Engineering: Durability, Products & Treatments

Vocabulary flashcards summarising major terms related to engineered wood products, preservative treatments, durability, and detailing discussed in the lecture.

Hygroscopic behavior

The property of wood to absorb or release moisture from the surrounding air, causing dimensional changes.

Equilibrium Moisture Content (EMC)

The moisture level at which wood is neither gaining nor losing water because it is in balance with ambient humidity and temperature.

Oven-drying method

Laboratory procedure that determines wood moisture content by weighing a sample before and after drying it in an oven to constant mass.

Electrical resistance moisture meter

Hand-held device that estimates wood moisture content by measuring the electrical resistance between two probes inserted into the timber.

Sawn timber

Wood cut directly from logs; size limited by tree diameter (≈450 mm) and typically produced from softwoods such as radiata pine.

Engineered wood product

Manufactured timber element (e.g., LVL, glulam, CLT) designed for enhanced strength, size, or performance beyond sawn lumber.

Glued Laminated Timber (Glulam)

Structural members made by gluing together multiple timber laminations, allowing long spans and curved shapes.

Laminated Veneer Lumber (LVL)

Engineered wood formed by bonding thin veneers with grain mostly parallel, yielding high strength and the ability to grade-optimize outer layers.

Cross-Laminated Timber (CLT)

Mass-timber panel built from perpendicular layers of boards; offers prefabrication, dimensional stability, and low weight (~400 kg/m³).

Finger-jointing

Serrated end-to-end joining technique that creates long, defect-free lumber pieces by gluing shorter segments together.

Oriented Strand Board (OSB)

Panel product made from strands of wood oriented and pressed with resin; often likened to strands from a ‘cheese grater’.

Timber I-beam

Composite beam with LVL or solid-wood flanges and an OSB/plywood web, optimized for high second moment of area and long spans.

Pole (round timber)

Whole log with bark removed, often preservative-treated for retaining walls, piles, or marine structures.

Preservative treatment

Process of pressure-impregnating chemicals into wood to protect against decay, insects, and moisture-related hazards.

Hazard class

Classification (H1.2–H6) indicating required preservative level based on exposure—from interior framing to marine contact.

Boron treatment (H1.2)

Low-hazard preservative using boron salts; identified by pink pigment and used for interior framing in NZ.

Chromated Copper Arsenate (CCA)

Green-tinted preservative (copper colour) containing chromium, copper, and arsenic; effective but raises environmental and disposal concerns.

Micronized Copper Quaternary (MCQ)

Newer copper-based preservative with finely ground copper particles and quats; viewed as less toxic alternative to CCA.

Alkaline Copper Quaternary (ACQ)

Water-borne preservative using copper and organic quaternary ammonium compounds, without arsenic or chromium.

Pink timber

Informal term for boron-treated framing lumber; the pink dye signals H1.2 protection.

Sacrificial layer

Non-structural covering placed over main timber to absorb weathering and be replaced when worn.

Rain screen

Ventilated cladding system that shields structural wood from direct rain while allowing drainage and drying.

End grain

Surface that exposes wood cells longitudinally; highly absorbent and therefore most vulnerable to moisture ingress.

UV weathering (silvering)

Discolouration and surface checking caused by ultraviolet light, giving timber a grey-silver appearance.

Leaky building crisis

1990s NZ construction failure where poor detailing (stucco cladding, no eaves/cavity) led to widespread framing decay.

Detailing (timber)

Designing joints, overhangs, flashings and ventilation paths to keep wood dry and durable.

Covered bridge

Timber bridge whose superstructure is roofed and side-clad to shield primary beams from weather.

Stainless steel fastener

Corrosion-resistant connector required in sea-spray or geothermal zones or with highly treated wood.

Hot-dip galvanized fastener

Steel hardware coated in thick zinc layer; suitable for most exterior applications outside severe marine zones.

Zinc-coated fastener

Standard electro-galvanized hardware intended for protected interior situations.

Sea spray zone

Coastal area where salt aerosols accelerate corrosion, necessitating stainless connectors and high-level treatments.

Ventilation path

Intentional air gap behind cladding or beneath members to facilitate drying and prevent moisture accumulation.

Moisture meter

Instrument (pin or pinless) used on site to assess timber moisture; readings >20–24 % indicate decay risk.

Differential swelling and shrinking

Uneven dimensional change within a member due to local moisture differences, potentially causing checks or splits.

Marine borer (Teredo worm)

Shipworm that tunnels into submerged timber, jeopardising durability of wharves and bridge piles.

Termite hazard

Risk of structural damage from wood-eating insects; higher in Australia, requiring H2 or above treatment.

Cavity wall

Construction with an air gap behind exterior cladding, improving drainage, ventilation, and durability.

CNC machining (for CLT)

Computer-controlled routing process that cuts windows, ducts, and openings in large CLT panels off-site.

Second moment of area

Geometric property indicating bending stiffness; timber I-beams place material at flanges to maximise this value.

Prefabrication

Factory production of dimensioned components (e.g., CLT panels) that speeds site erection and reduces waste.

Circular economy (timber waste)

Concept of designing timber products for reuse or safe disposal; challenged by CCA-treated material.

Carcinogen (arsenic in CCA)

Cancer-causing substance; free arsenic limits CCA use and complicates burning or landfill disposal.

Building Code B2 Durability

NZ code clause requiring building materials (including treated timber) to last at least 50 years in service.

NZS 3603

New Zealand Standard that provides design and durability requirements for timber structures.

Australian H2 class

Preservative level used for termite-prone Australian framing; higher than NZ H1.2.

H3.2

Treatment level for above-ground exterior timber exposed to weather, typically using CCA or copper-based systems.

H4

Preservative class for timber in ground contact or constantly wet environments, such as retaining walls.

H5

Higher treatment level for in-ground or fresh-water structural members requiring 50-year durability.

H6

Highest hazard class for marine exposure where timber is subject to saltwater and marine borers.