# WPC substructures and fixings: design the complete deck

Canonical: https://woodplasticcomposite.net/guides/wpc-substructure-fixings-drainage-design/
Language: en
Updated: 2026-10-01
Version: 1
Review: Technical and language review not yet recorded

## Summary

A deck is a system. Board performance cannot compensate for inadequate supports, incompatible fixings or details that trap water and prevent movement.

## The technical principle

Loads must pass through the boards, their connections and the supporting structure. Thermal and moisture movement also need an intentional path. A fixing arrangement that restrains every movement can introduce stresses, while insufficient restraint can allow displacement. Joist material, anchorage and stability need their own assessment.

https://woodplasticcomposite.net/guides/wpc-substructure-fixings-drainage-design/#technical-principle

## What to specify and verify

Use the selected product's instructions for support spacing, end support, fastening and permitted overhang. Coordinate clearances at walls, drainage beneath the deck and access for inspection. Do not assume a composite landscaping bearer is a structural joist or that a decking board can serve as one.

https://woodplasticcomposite.net/guides/wpc-substructure-fixings-drainage-design/#specification

## Application and common mistakes

At a butt joint, confirm how both ends are supported and fixed without blocking drainage or required movement. Avoid substituting clips because they look similar. For Green Plank projects, request the complete system detail for the proposed profile and substructure before preparing quantities or construction drawings.

https://woodplasticcomposite.net/guides/wpc-substructure-fixings-drainage-design/#application

## 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.

https://woodplasticcomposite.net/guides/wpc-substructure-fixings-drainage-design/#green-plank-project

## Key points

Support: Verify load path and end support.
Movement: Coordinate restraints and clearances.
Water: Maintain drainage and inspection access.

## Comparison

Specification check | Evidence to request
Support | Verify load path and end support
Movement | Coordinate restraints and clearances
Water | Maintain drainage and inspection access

## Can I mix clips from different decking systems?

Only with documented compatibility and approval for the intended detail; appearance is insufficient.

## Sources

1. Klyosov, A. A. (2007). Wood–Plastic Composites. Chapters 7, 10 and 12; pp. 225–234, 356–368, 383–396. — https://doi.org/10.1002/9780470165935
2. Green Plank — product information and technical enquiries — https://greenplank.eu/