organic / Timber / Structural Timber

Spotted Gum, structural batten & post, various grades and sizes (Specified by section size)

Premium Australian eucalyptus hardwood structural members graded F17-F34 per AS 2082. Density 950 kg/m3, MOE 19.8 GPa, MOR 142 MPa, Janka 11.0 kN, Durability Class 1, Joint Group JD1. For load-bearing posts, beams, battens, pergola framing, and heavy timber construction.

Atlas code

ORG-TBR-ST-002

organictimberstructural-timberspotted-gumhardwoodeucalyptusstructural-posts

Spotted Gum, structural batten & post, various grades and sizes (Specified by section size)

At-a-glance signals

Overview

Executive summary

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.

Best when…

Exceptional structural grades F17-F34 seasoned (AS 2082) — among strongest Australian timbers
Strength Group SD2 / Joint Group JD1 — superior connection performance
Durability Class 1 above ground (40+ years without treatment, AS 5604)
Natural termite resistance (heartwood) — no chemical treatment required above ground
BAL-29 bushfire compliance per AS 3959 Appendix F
Janka 11.0 kN — excellent fixing retention and impact resistance
100% Australian grown from sustainably managed native forests
Beautiful natural appearance for exposed structural applications
Carbon-sequestering material (~850 kg CO2/m3 stored)
Long structural service life 60-100+ years with proper design

Top advantages

01 Exceptional structural grades F17-F34 seasoned (AS 2082) — among strongest Australian timbers
02 Strength Group SD2 / Joint Group JD1 — superior connection performance
03 Durability Class 1 above ground (40+ years without treatment, AS 5604)
04 Natural termite resistance (heartwood) — no chemical treatment required above ground
05 BAL-29 bushfire compliance per AS 3959 Appendix F

Top limitations

01 Premium pricing — F27 structural significantly more expensive than treated pine framing
02 High density (950 kg/m3) increases dead load in structural calculations
03 Pre-drilling MANDATORY for all connections — direct nailing/screwing causes splitting
04 Limited availability in large post sections (>140x140mm) — often mill-order only
05 Significant tool wear — tungsten-carbide blades essential for all cutting/drilling

Technical

Physical ·8

Density: 950 kg/m3 Air-dry density at 12% moisture content. Same species as ORG-TBR-ST-001 — Corymbia maculata. Range 940-990 kg/m3. Structural grade timber is selected for consistent density. Sources: WoodSolutions, QTimber, AS 1720.2.
Specific gravity: 0.95 Specific gravity at 12% MC. High density delivers structural advantage but increases dead load in engineering calculations.
Porosity: 8-12 % Diffuse-porous structure typical of eucalyptus species. Low porosity contributes to structural density and connection holding power.
Water absorption: 10-15 % Equilibrium moisture content. Structural timber kiln-dried to 10-15% MC. Target 12% MC for most Australian climate zones. Moisture content affects structural capacity — AS 1720.1 provides modification factors for MC > 15%.
Hardness: 11.0 kN Janka hardness rating. Critical for structural connection design — Joint Group JD1 reflects high nail/screw holding capacity. Substantially harder than Blackbutt (9.1 kN) and Jarrah (8.5 kN). Sources: WoodSolutions, QTimber.
UV resistance: Moderate Moderate UV resistance. Exposed structural members will silver/grey over 6-12 months. For colour retention on exposed beams/posts, apply penetrating oil or UV-protective coating. Many designers specify natural weathering for exposed structural elements.
Chemical resistance: Good Good chemical resistance from natural heartwood extractives. Avoid direct contact with cementitious materials (alkaline) which can cause surface degradation and staining. Use separation membranes where timber contacts concrete or masonry.
pH tolerance: 4-8 pH Heartwood pH approximately 4.5-5.5 (mildly acidic). Use stainless steel (316 coastal, 304 inland) or hot-dip galvanised structural connectors. Plain steel bolts/brackets will corrode and cause black staining.

Mechanical ·5

Tensile strength: 100-130 MPa Tensile strength parallel to grain. Structural design uses characteristic bending strength per AS 1720.1 rather than direct tensile testing. Estimated from MOR and typical hardwood relationships.
Compressive strength: 55-70 MPa Compressive strength parallel to grain. Critical for post and column design. Strength Group SD2 provides characteristic compressive strength approximately 55-70 MPa per AS 1720.1. Column design considers slenderness ratio and effective length per AS 1720.1 Section 3. Source: WoodSolutions, AS 1720.1.
Flexural strength: 142 MPa Modulus of Rupture (MOR). Characteristic value 141.8 MPa (The Wood Database). F-grade stress grades represent design values with safety factors: F17 = 17 MPa, F22 = 22 MPa, F27 = 27 MPa, F34 = 34 MPa characteristic bending stress. The difference between MOR (142 MPa) and design stress (e.g., F27 = 27 MPa) reflects safety factors, size effects, and duration of load adjustments per AS 1720.1. Sources: The Wood Database, AS 1720.1, AS 2082.
Impact resistance: 80-110 J/m Excellent impact resistance — the primary Australian species for tool handles subject to high-impact forces. Interlocked grain resists splitting under impact. More flexible than many other hardwood species. Joint Group JD1 reflects superior connection performance under dynamic loading. Source: QTimber, WoodSolutions.
Creep resistance: Excellent Excellent creep resistance under sustained loading. Strength Group SD2 provides high long-term load factors per AS 1720.1. Duration of load factor k1 applies per standard. Spotted Gum is notably resistant to cracking during drying and more flexible than many species — widely used for stockyard rails where impact resistance under sustained loading is critical. Source: QTimber, WoodSolutions.

Sustainability & Health

Embodied carbon & energy ·7

Embodied carbon: 150-350 (gross); net negative including sequestration kg CO2-eq/m3 Cradle-to-gate embodied carbon for sawn Australian hardwood. Structural grading adds minimal processing energy beyond standard milling. Timber stores approximately 850 kg CO2/m3 through carbon sequestration. Net carbon balance typically carbon-negative. Source: Timber Development UK, IStructE guidance.
Carbon footprint: -500 to -700 (net, including sequestration) kg CO2-eq/m3 Including biogenic carbon sequestration. Net carbon-negative: approximately -500 to -700 kg CO2-eq/m3. Carbon stored for the structural service life (60-100+ years). Replacing steel or concrete with Spotted Gum structural timber provides significant carbon reduction.
Embodied energy: 500-1500 MJ/m3 Primary energy for harvesting, kiln drying, and milling. Kiln drying accounts for 60-70% of total. Air-drying reduces embodied energy but increases lead time and may not achieve structural MC requirements consistently.
Water footprint: 5-20 L/kg Natural forest growth — minimal processing water. Very low water footprint compared to steel, concrete, or manufactured building materials.
Recycled content: 0 % New structural timber from sustainably managed forests: 0% recycled content. Structural grade requires virgin timber for grading certification (AS 2082). Reclaimed structural Spotted Gum available from demolition at premium pricing but cannot be re-graded to original F-grade without testing.
Renewable content: 100 % 100% renewable natural material from sustainably managed native forests.
Circular score: 9 /10 Excellent circular economy credentials. Renewable, biodegradable, reusable (reclaimed structural timber market), recyclable (mulch/biomass). Long service life maximises value retention. Structural sections can be repurposed at end of original building life.

Compliance & Fire

Fire performance ·6

Combustibility class: Combustible — Group 3 (AS 5637.1), BAL-29 compliant (AS 3959) Combustible material — Group 3 per AS 5637.1. BAL-29 compliant per AS 3959:2018 Appendix F (density >750 kg/m3 at 12% MC). Structural sections (>35mm thick) develop protective char layer in fire, maintaining residual structural capacity. AS 1720.4 provides design methods for fire resistance of structural timber members. Sources: AS 3959:2018, AS 1720.4, AS 5637.1.
Fire resistance level: 60-120 minutes Fire resistance depends on section size and char rate. Australian hardwood char rate approximately 0.5-0.6 mm/min. Structural sections: 90x90mm post: ~75 min to lose 50% section. 140x140mm post: ~115 min. Heavy timber construction can achieve significant fire resistance periods. Design per AS 1720.4. Source: AS 1720.4, timber fire engineering literature.
Ignition temp: 300-350 degC Piloted ignition temperature for dense eucalyptus hardwood. High density provides higher thermal inertia.
Flame spread index: 100-150 FSI Flame Spread Index for dense Australian hardwood. Group 3 material per AS 5637.1.
Smoke dev. index: 150-250 SDI Moderate smoke production. Dense hardwood — slower, more complete combustion produces proportionally less smoke per unit mass than lighter species.
Heat release rate: 150-250 kW/m2 Peak heat release rate for dense hardwood. High density provides slower, more sustained combustion. Larger structural sections perform significantly better in fire than thin cladding boards due to char layer formation protecting the structural core.

Cost & Lifecycle

Capex & lead time ·6

Material cost (range): 8-65 per lineal metre (size dependent) AUD/lm Supply only, ex-GST, per lineal metre. Pricing varies significantly by section size. 70x35mm F27: ~$8-12/lm. 90x45mm F27: ~$14-20/lm. 140x35mm F27: ~$16-22/lm. 240x45mm F27: ~$35-50/lm. 290x45mm F27: ~$45-65/lm. Post sections (90x90, 115x115, 140x140): quote-dependent. Sources: Canterbury Timber, Bendigo Building Timber, Geelong Timber Supplies, Nationwide Timber, JBM Timber.
Material cost (per unit): 3500-6000 AUD/m3 Volume pricing for structural grade Spotted Gum. F27 structural: approximately $3,500-6,000/m3 depending on section size and grade. Premium over treated pine structural framing (MGP10/MGP12) is significant but justified by durability, aesthetics, and no treatment requirement.
Lead time: 5-35 days Standard stock sizes (70x35, 90x35, 90x45 F27): 5-10 days ex-warehouse from major suppliers. Large beam sizes (190x45, 240x45, 290x45): 10-21 days, may require mill scheduling. Post sections (90x90, 115x115, 140x140+): often mill-order, 14-35 days. Sources: Canterbury Timber, Nationwide Timber, Geelong Timber Supplies.
Lifecycle cost: 200-450 AUD/m2 50-year lifecycle cost for structural applications. Excellent value due to 60-100+ year service life with minimal maintenance. Structural timber requires less maintenance than cladding (no coating required for structural integrity). Annualised cost is very competitive with steel and concrete for exposed structural applications.
Annual maintenance: 0.20-2.00 AUD/lm/year Very low annual maintenance. Structural members: visual inspection every 5-10 years (minimal cost). Coated exposed members: recoat oil every 2-3 years. Unfinished structural (most common): near-zero maintenance cost — structural integrity maintained by natural durability.
Market availability: Good (standard sizes); Moderate (large sections) Good availability for standard F27 sections (70x35 to 140x45) through major structural timber suppliers nationally. Larger beam sections (190x45+) and posts (90x90+) may require advance ordering or mill scheduling. F34 grade less commonly stocked — typically mill-order. Supply from sustainably managed native forests in NSW and Queensland.

Service life & durability ·3

Expected lifespan: 60-100+ years Durability Class 1 above ground per AS 5604 — minimum 40 years expected. Structural Spotted Gum in well-detailed above-ground applications routinely achieves 60-100+ years. Heritage bridges and wharves demonstrate 100+ year performance. In-ground applications: Class 2 (15-25 years) without treatment; H4 or H5 treatment extends in-ground life significantly. Source: AS 5604, WoodSolutions.
Maintenance interval: 5-10 years Structural inspection interval per AS 1720.1 and NCC requirements. Visual inspection for structural integrity: every 5-10 years. Coating maintenance (if finished): 1-5 years depending on finish type. Unfinished exposed structural members: inspect for connection integrity and timber defects every 5-10 years.
Warranty period: 25 years Structural timber warranty varies by supplier and application. Typically 25 years for above-ground structural applications with compliant installation and maintenance. Some suppliers offer longer structural warranties. Source: Industry practice.

Layer D

Where it's used

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

Where it's used

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