This standard specifies the method for determining the thermal conductivity of timber using a guarded hot-plate apparatus. It covers the principle, apparatus, specimen preparation, test procedure, and calculation method. The resulting thermal conductivity value (k-value) is essential for the thermal design and energy performance analysis of buildings.
Method of determination of thermal conductivity of timber
Quick Reference Values
Specimen Thickness25 mm to 50 mm
Specimen Size (for 30cm apparatus)300 x 300 mm
Specimen Size (for 60cm apparatus)600 x 600 mm
Test Equilibrium ConditionSuccessive readings differ by < 1%
Standard Test ConditionOven-dry condition
Time Interval for successive observationsNot less than 30 minutes
Key Formulas
λ = (Q * d) / [A * (t1 - t2)] — Calculation of thermal conductivity, where Q is heat flow, d is specimen thickness, A is area, and (t1-t2) is the temperature difference.
Practical Notes
Moisture content is the most critical variable affecting timber's thermal conductivity. Ensure specimens are conditioned to the specified state (e.g., oven-dry) for accurate and repeatable results.
The direction of heat flow relative to the wood grain (parallel or perpendicular) significantly impacts the result and must be recorded and reported.
The test is highly sensitive and requires a stable laboratory environment and a properly calibrated guarded hot-plate apparatus as per IS 3346.