SPF SS (Select Structural)
Grade
Choose the highest visual structural class, with the fewest knots, for beams, joists and truss bottom chords where deflection limits and load capacity govern the design.
Values for the SS condition
Other SPF tempers and conditions
SPF is listed in 5 conditions; see the grade overview at SPF.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Surfaced green, MC > 19 % | Pick surfaced-green stock when cost rules and the frame can dry in place; strength and stiffness are about 20–40 % lower and shrinkage, checking and twist risk are high. | — | 15 | 1.3 | — | 0.18 W/m·K |
Stud grade | Use only for load-bearing wall studs: the grade guarantees parallel-to-grain compression performance and is not suited to long-span bending members. | — | 15 | 1 | — | 0.12 W/m·K |
KD-HTDefault KD-HT No.2 & Btr | Default for framing studs and joists: kiln dried to a moisture content of ≤19 %, dimensionally stable and ready to be closed in without further on-site drying. | — | 22 | 1 | — | 0.12 W/m·K |
MSR 1650Fb-1.5E | Pick machine stress rated stock, graded piece by piece for stiffness, when scatter must be low — light truss chords and engineered I-joist flanges. | — | 30 | 1 | — | 0.12 W/m·K |
SSThis page Select Structural | Choose the highest visual structural class, with the fewest knots, for beams, joists and truss bottom chords where deflection limits and load capacity govern the design. | — | 32 | 1 | — | 0.12 W/m·K |
What is SPF SS?
SPF SS is SPF in the SS grade — choose the highest visual structural class, with the fewest knots, for beams, joists and truss bottom chords where deflection limits and load capacity govern the design. SPF SS has a tensile strength of 32 MPa (4.64 ksi), stronger than 62% of natural material grades. Elongation at break is 1% and the elastic modulus is 10.3 GPa (1.49 Msi). SPF SS has a density of 0.42 g/cm³ (0.0152 lb/in³), lighter than 84% of natural material grades. KD-HT is the default condition FabDigit quotes; SS is available on request or by drawing note.
Advantages
- Easy to machine — 95/100, better than 100% of natural material grades
- Lightweight — 0.42 g/cm³ (0.0152 lb/in³), better than 84% of natural material grades
Limitations
- Limited service temperature — 65°C (149 °F), worse than 88% of natural material grades
- Needs corrosion protection — 30/100, worse than 77% of natural material grades
SPF SS properties
Typical room-temperature values for SPF SS; 12 are specific to this condition. Other listed values are SPF reference data and may not represent this condition. Bars are the position among natural material grades.
Physical2
SPF SS has a density of 0.42 g/cm³ (0.0152 lb/in³), lighter than 84% of natural material grades.
Mechanical9
SPF SS has a tensile strength of 32 MPa (4.64 ksi), stronger than 62% of natural material grades. Elongation at break is 1% and the elastic modulus is 10.3 GPa (1.49 Msi).
Thermal5
SPF SS is rated for continuous service to 65°C (149 °F). It conducts heat at 0.12 W/m·K (0.0693 BTU/hr·ft·°F), worse than 70% of natural material grades. Thermal expansion is 4.5 µm/m·K (2.5 µin/in·°F).
Electrical1
SPF SS has an electrical resistivity of 5×10⁹ Ω·m.
Chemical & Environmental1
Corrosion resistance is poor (30/100), worse than 77% of natural material grades.
Sustainability4
Producing a kilogram of SPF SS takes about 9 MJ of energy and emits 0.4 kg of CO₂ — less than 71% of natural material grades. Typical recycled content is 0%.
Manufacturability2
SPF SS's machinability is excellent (95/100, better than 100% of natural material grades).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SPF SS
Is SPF easy to machine?
Sawing, planing, drilling and mortising are very easy with either high-carbon steel or carbide tooling. The soft fibres raise fuzz, so keep edges sharp and feed rates on the high side, and expect chip-out at knots.
Can SPF be welded?
Not applicable; join with nails, screws, toothed plate connectors or structural adhesives (PUR, EPI, resorcinol).
Can SPF be formed, bent or molded?
Cannot be bent cold. Curved members and long spans are produced by steam softening or by laminating and gluing (glulam, finger-jointed stock).
What surface finishes work on SPF?
Sand, then seal the earlywood/latewood difference with a primer or waterborne sealer before topcoating. Exterior parts need ACQ or CA pressure treatment, or a water-repellent oil-wax finish.
SPF chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| cellulosecrystalline and amorphous cellulose | 40 – 45 | 43 |
| hemicellulosemainly galactoglucomannan | 25 – 30 | 27 |
| ligninguaiacyl lignin typical of softwoods | 26 – 31 | 28 |
| extractivesresins, fatty acids, terpenes | 1 – 5 | 2 |
| ashinorganic ash | 0.2 – 0.5 | 0.3 |
SPF SS — frequently asked
What is SPF SS used for?
SPF SS is typically used for light-frame construction studs, roof trusses, packaging crates, furniture framing and general dimensional lumber. In short: standard North American framing lumber; easiest-working structural softwood; needs treatment for exterior use.
What is the tensile strength of SPF SS?
SPF SS has a typical tensile strength of 32 MPa (4.64 ksi) — stronger than 62% of natural material grades. Strength varies by condition: see the 5 listed tempers.
Is SPF SS easy to machine?
Yes — machinability is rated excellent (95/100, better than 100% of natural material grades). Sawing, planing, drilling and mortising are very easy with either high-carbon steel or carbide tooling. The soft fibres raise fuzz, so keep edges sharp and feed rates on the high side, and expect chip-out at knots.
Can SPF SS be welded?
Not applicable; join with nails, screws, toothed plate connectors or structural adhesives (PUR, EPI, resorcinol).
What surface finishes work on SPF SS?
Sand, then seal the earlywood/latewood difference with a primer or waterborne sealer before topcoating. Exterior parts need ACQ or CA pressure treatment, or a water-repellent oil-wax finish.
Can SPF SS be formed, bent or molded?
Cannot be bent cold. Curved members and long spans are produced by steam softening or by laminating and gluing (glulam, finger-jointed stock).
What is the maximum service temperature of SPF SS?
SPF SS is rated for continuous use to about 65°C (149 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- ASTM D1990 — Establishing Allowable Properties for Visually Graded Dimension Lumber — ASTM International (2019)
- ASTM D2555 — Establishing Clear Wood Strength Values — ASTM International (2017)
- Wood Handbook — Wood as an Engineering Material, GTR-190 — USDA Forest Products Laboratory (2021)
- NDS Supplement — Design Values for Wood Construction (SPF tables) — American Wood Council (2018)
- Standard Grading Rules for Canadian Lumber — NLGA (2022)
- Inventory of Carbon & Energy (ICE) v3 — sawn softwood — University of Bath / Circular Ecology (2019)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.