At a glance
Composite boards expand and contract with temperature. Gaps and fixing arrangements must follow the exact product's instructions and the installation conditions.
Key points
- Calculation: Use product-specific α and temperature range.
- Fixings: Identify fixed and moving points.
- Clearance: Follow the complete installation detail.
The technical principle #
A simplified estimate is ΔL = α × L × ΔT, where α is the linear expansion coefficient, L the initial length and ΔT the temperature change. Direction and temperature range matter. Surface temperatures can differ substantially from air temperature, particularly in direct sun.
What to specify and verify #
As an illustrative calculation, α = 40 × 10⁻⁶/K, L = 4 m and ΔT = 50 K give 8 mm of total length change. These are assumed values, not Green Plank measurements or a recommended joint width. How movement is distributed depends on the fixing arrangement.
Application and common mistakes #
Ask for the tested coefficient, installation-temperature guidance, fixed and sliding points, and clearances at walls and ends. Moisture swelling and irreversible shrinkage are separate effects. A standard gap copied from another manufacturer's board can be inadequate even when the two products look similar.
Discuss your project with Green Plank #
For a Green Plank specification, request samples and current technical documents for the exact profile and intended application. Use the Green Plank link in Sources to explore the range and make an enquiry. Commercial disclosure: this portal features Green Plank. General material science does not certify any particular product.
Project specification checklist
| Specification check | Evidence to request |
|---|---|
| Calculation | Use product-specific α and temperature range |
| Fixings | Identify fixed and moving points |
| Clearance | Follow the complete installation detail |
Common questions
Should each end always get half the movement allowance?
No. Movement distribution depends on restraints and the manufacturer's fixing system.
Question permalink ↗Sources & further reading
- Klyosov, A. A. (2007). Wood–Plastic Composites. Chapter 10; pp. 356–368. ↗John Wiley & Sons · Book · 2026-10-01
- Green Plank — product information and technical enquiries ↗Green Plank · Web reference · 2026-10-01
Cite this page
J. A. Gill. “WPC thermal expansion: calculate movement before gaps” Version 1. Updated 2026-10-01. https://woodplasticcomposite.net/guides/wpc-thermal-expansion-decking-gaps/
Author profile
Author: J. A. Gill
WPC and natural-fibre composite specialist · Innovator, inventor, product designer and entrepreneur
Original educational article informed by Klyosov (2007). Modern project applications are editorial synthesis. This is not a product certificate or a substitute for project-specific design.
General material information is not product certification or project-specific engineering advice.
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