What durability class is required for timber decking?

Timber decking is classified as Use Class 3.2 (above ground, not covered, subject to frequent wetting) or Use Class 4 (in ground contact for posts/subframe). For the deck boards themselves, specify minimum Durability Class 3 for untreated timber (European Larch, Douglas Fir) or DC 1–2 for maximum longevity (Western Red Cedar, Teak, thermally modified timber).

Timber decking is classified as Use Class 3.2 (above ground, not covered, subject to frequent wetting) or Use Class 4 (in ground contact for posts/subframe). For the deck boards themselves, specify minimum Durability Class 3 for untreated timber (European Larch, Douglas Fir) or DC 1–2 for maximum longevity (Western Red Cedar, Teak, thermally modified timber). Subframe timbers in ground contact require DC 1–2 or preservative treatment to Use Class 4.

Why this matters

This question relates to Timber Decking Specification: Durability Classes & Species Selection, which covers the broader topic in detail. Understanding this specific aspect helps architects, builders, and timber dealers make informed specification decisions.

For full context and additional technical detail, see our comprehensive guide:

→ Timber Decking Specification: Durability Classes & Species Selection

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About this answer

This answer is part of the PuurModulair Knowledge Base — comprehensive timber specification guidance for architects, builders, and dealers across the UK, EU, and Scandinavia.