Spotted Gum, structural batten & post, various grades and sizes (Specified by section size)
Structural Timber
ATLAS CODE
ORG-TBR-ST-002
Category organic
Material Family Timber
Regulatory Status Combustible — Group 3 (AS 5637.1), BAL-29 compliant (AS 3959)
Density
950 kg/m3
Carbon (A1-A5)
150-350 (gross); net negative including sequestration kg CO2-eq/m3
Fire Class
Combustible — Group 3 (AS 5637.1), BAL-29 compliant (AS 3959)
Lifespan
60-100+ years
Description
Spotted Gum (Corymbia maculata) structural battens, posts, and beams represent the highest performance category of Australian native hardwood structural timber. Visually stress-graded to F17, F22, F27, or F34 per AS 2082, with Strength Group SD2 (seasoned) providing a modulus of elasticity of 19.8 GPa and modulus of rupture of 142 MPa. Available in kiln-dried (KD) sections from 70x35mm battens to 290x45mm beams and 140x140mm+ posts, each grade-stamped for NCC structural compliance. Durability Class 1 above ground (40+ years per AS 5604) and natural termite resistance eliminate chemical treatment requirements for heartwood in above-ground applications. BAL-29 bushfire compliant per AS 3959 Appendix F. Joint Group JD1 (seasoned) delivers superior connection holding power critical for structural assemblies.
Typical Uses
- Structural posts and columns
- Structural beams and bearers
- Pergola and pavilion framing
- Deck substructure (bearers and joists)
- Structural battens and purlins
- Exposed feature beams (interior and exterior)
- Bushfire zone structural framing (BAL-29)
- Heritage restoration structural members
Size
Primary Form [70x35mm / To / 290x45mm / (battens/beams); / 90x90mm / To / 140x140mm+ / (posts)]
Dimensional Tol. ± [+/- 1.0mm thickness and width] mm
Recycled Content 0
Renewable Content 100
Recyclability 95
Embodied Carbon 150-350 (gross); net negative including sequestration kg CO2-eq/m3
Embodied Energy 500-1500 MJ/m3
EPD Available No
Advantages
Exceptional structural grades F17-F34 seasoned (AS 2082) — among strongest Australian timbersStrength Group SD2 / Joint Group JD1 — superior connection performanceDurability Class 1 above ground (40+ years without treatment, AS 5604)Natural termite resistance (heartwood) — no chemical treatment required above groundBAL-29 bushfire compliance per AS 3959 Appendix FJanka 11.0 kN — excellent fixing retention and impact resistance100% Australian grown from sustainably managed native forestsBeautiful natural appearance for exposed structural applicationsCarbon-sequestering material (~850 kg CO2/m3 stored)Long structural service life 60-100+ years with proper design
Cautions
Premium pricing — F27 structural significantly more expensive than treated pine framingHigh density (950 kg/m3) increases dead load in structural calculationsPre-drilling MANDATORY for all connections — direct nailing/screwing causes splittingLimited availability in large post sections (>140x140mm) — often mill-order onlySignificant tool wear — tungsten-carbide blades essential for all cutting/drillingHeavy material requires mechanical handling for large sections (lifting equipment)Structural engineering specification required for load-bearing applicationsSapwood susceptible to lyctid borer — must be excluded or treated per AS 1604
TECHNICAL DATA: PERFORMANCE PROPERTIES ORG-TBR-ST-002
Density (Dry) 950 kg/m3
Specific Gravity 0.95
Porosity 8-12 %
Water Absorption 10-15 %
Hardness 11.0 kN
UV Resistance Moderate
Chemical Resistance Good
pH Tolerance 4-8 pH
Available Colors
Natural heartwood: light brown to pale gold (freshly dressed)Natural heartwood: mid brown to warm chocolate (common range)Natural heartwood: dark brown to deep chocolate (dense growth)Weathered/silvered: pale grey to silver-grey (12+ months unfinished exposure)Oiled: enhanced warm brown tones (natural, tung, or Danish oil)
Surface Finishes
Natural/unfinished — most common for structural members, weathers to silver-greyPenetrating oil (Cutek, Intergrain) — enhances grain, recoat every 2-3 years for exposed elementsClear UV-protective sealant — maintains colour for exposed beams/postsPre-finished factory coating — available from premium suppliers for consistent finishCharred surface (Shou Sugi Ban) — can be applied to structural elements for aesthetic/durability
Texture Options
Dressed all round (DAR) with pencil-round edges — standard structural finishRough-sawn — rustic/industrial aesthetic for exposed structurePlaned smooth (PAR) — premium appearance for exposed beams and postsWire-brushed — accentuated grain texture for feature elementsNatural fiddleback figuring — premium boards with distinctive wavy grain
Pattern Options
Exposed structural beams — horizontal or raking (roof)Exposed structural posts — vertical feature elementsPergola/pavilion framing — post-and-beam constructionStructural battens — repeated parallel elements for screens or substructureFeature trusses — triangulated structural elementsCantilever beams — projecting structural elements for shade or awnings
Compressive Strength 55-70 MPa
Tensile Strength 100-130 MPa
Flexural Strength 142 MPa
Elastic Modulus 19.8 GPa
Impact Resistance 80-110 J/m
Creep Resistance Excellent
Abrasion Resistance Excellent
Thermal Conductivity 0.19-0.21 W/mK
Thermal Resistance 0.17-0.74 m2K/W
Specific Heat Capacity 1400-1600 J/kgK
Thermal Expansion 0.003-0.005 mm/mK
Ignition Temperature 300-350 degC
Sound Transmission Class (STC) 30-45 STC
Noise Reduction Coeff. (NRC) 0.05-0.10 NRC
Optical
Light Transmittance 0 %
Light Reflectance (LRV) 25-40 %
Electrical
Electrical Conductivity Insulator (dry) S/m
Spotted Gum (Corymbia maculata) has served as the backbone of Australian heavy construction since the colonial era. Historic bridges, wharves, railway sleepers, and mining timbers relied on its exceptional strength-to-weight ratio and natural durability. The species was reclassified from Eucalyptus maculata to Corymbia maculata in 1995. The development of mechanical stress grading (MSG) and machine-graded pine (MGP) systems in the 1980s-1990s led to standardised F-grade classifications under AS 2082, allowing engineers to specify precise structural properties. Despite competition from engineered wood products (LVL, glulam) and steel, solid Spotted Gum structural timber maintains strong demand for exposed structural applications — pergolas, pavilions, landscape structures, and heritage restoration — where its natural aesthetics and durability complement structural performance. The species' listing in AS 3959 Appendix F for BAL-29 bushfire construction has further expanded its specification in fire-prone regions.
SAFETY, ECOLOGY & INSTALLATION ORG-TBR-ST-002
Flame Spread Index 100-150 FSI
Smoke Developed Index 150-250 SDI
Combustibility Class Combustible — Group 3 (AS 5637.1), BAL-29 compliant (AS 3959)
Ignition Temperature 300-350 degC
Fire Resistance Rating 60-120 minutes
Heat Release Rate 150-250 kW/m2
Toxicity of Combustion Low
Embodied Carbon (A1-A3) 150-350 (gross); net negative including sequestration kg CO2-eq/m3
Embodied Energy 500-1500 MJ/m3
Water Footprint 5-20 L/kg
EPD Available No
LEED Points 6-9 points
Circular Economy Score 9 /10
VOC Emissions <E1 (very low) ug/m3
Skill Level Specialist structural carpenter (hardwood experience)
Crew Size 2-6 people
Installation Time 2-8 hours/10lm
Curing Time 0 hours
Temperature Range 5-40 degC
Humidity Range 30-75 % RH
Required Tools
Heavy-duty drop saw / circular saw with tungsten-carbide-tipped (TCT) blade — essential for hardwoodPre-drilling equipment — MANDATORY for all connections (combination drill/countersink bits)High-torque impact driver for coach screws and structural screwsAuger bits for bolt holes (12mm, 16mm, 20mm common structural bolt sizes)Chisel set for housings and notch jointsMoisture meter (pin-type) for MC verificationSpirit level, plumb bob, string lines, laser level for structural alignmentLifting equipment (crane, forklift, chain block) for large beams and postsStructural connection hardware: galvanised/stainless steel bolts, coach screws, framing bracketsPPE: P2 dust mask (hardwood dust), hearing protection, eye protection, steel-cap boots
Certifications Required
Licensed builder or qualified structural carpenter (Australian state licensing)Working at heights certification (for elevated beam/rafter installation)Construction White Card (general construction induction)Rigger/dogger certification (for crane lifting of large structural members)Knowledge of AS 1684 (Residential Timber-Framed Construction)Knowledge of AS 1720.1 (Timber Structures — Design Methods) for non-residential structural applicationsFamiliarity with AS 3959 for BAL zone construction
Weather Limitations
Do not install during rain — structural connections require dry timber at target MCProtect delivered structural timber from rain and ground moisture with bearers and coveringAllow timber to acclimatise to site conditions for minimum 48 hours before installationEnsure foundations/footings are cured and ready before post installationProvide temporary bracing during construction until permanent connections are completed
COMMERCIAL, LOGISTICS & REGULATORY ORG-TBR-ST-002
Material Cost 8-65 per lineal metre (size dependent) AUD/lm
Installation Cost 15-80 per lineal metre (application dependent) AUD/lm
Annual Maintenance 0.20-2.00 AUD/lm/year
Lifecycle Cost (50yr) 200-450 AUD/m2
Market Availability Good (standard sizes); Moderate (large sections)
Lead Time 5-35 days
Supply & Logistics
Design Life 60-100+ years
Warranty Period 25 years
Maintenance Interval 5-10 years
Service Temp Range -10 to 65 degC
Dimensional Stability 0.3-0.4 per 1% MC % change
Certifications Held
AS 2082 — Timber — Hardwood — Visually stress-graded for structural purposes (F17-F34)AS 1720.1 — Timber structures Part 1: Design methodsAS 1720.2 — Timber structures Part 2: Timber propertiesAS 2796 — Timber — Hardwood — Sawn and milled products (appearance grading)AS 1604 — Specification for preservative treatment (when treatment required)AFS (Australian Forestry Standard) / PEFC certifiedFSC certification available from select suppliersResponsible Wood certification (PEFC endorsed)VOC emissions below E1 (WHO levels)No formaldehyde emissions (natural untreated timber)GECA eligible (Good Environmental Choice Australia)
Fire Code Compliance
AS 3959:2018 — Construction of buildings in bushfire-prone areas (BAL-29 compliant)AS 5637.1 — Fire hazard properties — Group 3 materialAS 1720.4 — Timber structures Part 4: Fire resistance of structural timber membersNCC 2022 Volume 1 Section C — Fire resistance (structural timber fire design)
Standards Compliance
NCC 2022 (National Construction Code) — structural and non-structural applicationsAS 1684 — Residential timber-framed construction (span tables, bracing, connections)AS 1720.1 — Timber structures Part 1: Design methods (engineering design)AS 1720.2 — Timber structures Part 2: Timber propertiesAS 5604 — Natural durability ratings (Class 1 above ground, Class 2 in-ground)AS 1170 — Structural design actions (loads for structural timber design)ASTM D143 — Standard test methods for small clear specimens of timberASTM E84 — Surface burning characteristicsISO 13061 — Physical and mechanical properties of woodISO 3129 — Wood — Sampling and general requirementsEN 350 — Durability of wood (Class 1 equivalent)EN 338 — Structural timber strength classes (D50-D60 equivalent)EN 14081 — Timber structures — Strength graded structural timber (equivalent methodology)
DISCLAIMER: This specification document is generated from the CLAD Materials Atlas Database. Information is for general guidance only and does not constitute professional engineering advice. Values are typical and may vary by batch, manufacturer, and production run. Verify suitability for specific project applications independently.