Overview
EN ISO 8970:2020 / ISO 8970:2020 - "Timber structures - Testing of joints made with mechanical fasteners - Requirements for timber density" specifies how to select and report pieces of structural timber used to determine the strength and stiffness of mechanical fastener joints. It is intended to be used together with a test standard that defines the mechanical test method. The standard ensures test results are representative of the timber to which they will be applied by controlling wood density sampling, conditioning and reporting.
Key topics and requirements
- Scope: Applies only to specimens of structural timber used in joint tests with mechanical fasteners.
- Conditioning: Wood must be at equilibrium at (65 ± 5) % RH and (20 ± 2) °C at testing; indicate whether equilibrium was reached by drying or moistening.
- Density measurement: Density for the actual moisture content is determined in accordance with ISO 13061-2.
- Statistical assumptions: The standard assumes wood density is normally distributed; any deviations must be reported.
- Mean density requirement: The mean density of selected pieces (ρm,sel) must meet the target timber mean (ρm,tar) within ±5% (i.e., 0.95·ρm,tar ≤ ρm,sel ≤ 1.05·ρm,tar).
- Variation requirement: The coefficient of variation (COV) of selected pieces (CV,ρ,sel) must be at least the target COV of the timber (CV,ρ,tar). A target density range covering [(1 − k)ρm,tar ; (1 + k)ρm,tar] is suggested, where k = 1.65·CV or 0.25 if CV is unknown.
- Corrections: If sampling requirements are not met, Annex A provides a method to correct observed resistances using a density-based correction (involving an exponent c); Annex B gives background and guidance.
- Test report content: Must include reference to ISO 8970:2020, wood species/group, conditioning method, densities of selected pieces, mean and COV, moisture content if measured, evidence of compliance or deviations, and any other relevant information.
Practical applications and users
Who uses EN ISO 8970:2020:
- Materials and structural testing laboratories performing mechanical fastener joint tests.
- Timber manufacturers and producers preparing test specimens to support product performance claims.
- Structural engineers and researchers interpreting joint test data for design and safety assessments.
- Certification bodies and regulatory authorities verifying test procedures and reporting quality.
Why it matters:
- Ensures test results are representative of intended timber applications by controlling density and statistical variation.
- Provides a transparent basis for correcting test outcomes when exact target density conditions cannot be achieved.
- Improves comparability and reliability of joint strength and stiffness data used in design and certification.
Related standards
- ISO 13061-2 - Determination of density for small clear wood specimens (referenced for density measurement).
- Use in conjunction with the specific product or test standard that defines the mechanical joint testing procedure.
