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Expansion Gap Calculator

Calculate wood expansion gaps for flooring, decking and cladding. Uses species shrinkage coefficients and climate zones. IS 1328, NWFA, EN 13226.

IS 1328 IndiaNWFA USAEN 13226 EU50 SpeciesPDF Report
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Expansion Gap β€” Calculator

Calculate wood expansion gaps for flooring, decking and cladding. Uses species shrinkage coefficients and climate zones. IS 1328, NWFA, EN 13226.

Units & Application
Unit System
Application
Grain Orientation
Species & Shrinkage Coefficient
Wood Species
Shrinkage Coefficient (S)
/ %MC
Per 1% MC change, tangential. Radial = S Γ— 0.55 (auto-applied).
Board Width
mm
Moisture Content & Climate
Installation MC (%)
%
Expected Min MC (%)
%
Expected Max MC (%)
%
Total Run Width
mm
Climate Zone
βœ“
Expansion Gap Results
β€”
mm
Gap Per Board
β€”
mm
Total End Gap
β€”
mm
Max Shrinkage
β€”
mm
Max Swelling
Formula Trace
🌿 Expansion Gap Calculator
Wood is hygroscopic β€” it absorbs and releases moisture, expanding across the grain in humid conditions and contracting in dry ones. This tool calculates exact gap allowances based on species shrinkage coefficients, moisture content range, and climate zone.
Where Used?
Solid Wood FlooringOutdoor DeckingWall CladdingDoor FramesTable TopsAcoustic Panels
Formulas
Movement = W Γ— S Γ— Ξ”MC (W=width, S=coeff/MC%, Ξ”MC=change %)Radial coeff β‰ˆ Tangential Γ— 0.55Gap per board = max(shrink, swell) Γ— 1.15 (15% safety factor)
FAQ
Why does India need bigger gaps?
Indian tropical/monsoon climate creates RH swings from ~40% dry to ~95% wet β€” a MC change of 8–14%. Northern Europe sees only 4–8% swing. Indian gaps need nearly double the allowance.
Does thermowood need expansion gaps?
Yes, but ~40–60% smaller. Thermal modification dramatically reduces the shrinkage coefficient β€” making thermowood ideal for Indian climate exterior decking.
ResourcesView the formulasFormula Library
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