Timber Retaining Wall Engineering

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What Is a Timber Retaining Wall?

Timber retaining walls use treated pine logs, hardwood sleepers, or engineered timber posts and rails to retain earth. They're a popular choice for residential gardens and landscapes where a natural aesthetic is desired. Suitable for retained heights up to approximately 1.2–1.5 metres.

Timber walls work on the same principle as concrete sleeper walls — horizontal members span between vertical posts. The key difference is the material properties: timber has lower strength and stiffness than concrete or steel, and it degrades over time in contact with soil.

Engineering Design Considerations

Timber treatment — Any timber in ground contact must be H4 treated (or H5 for marine environments). Untreated or under-treated timber will rot within 5–10 years. Our designs specify minimum treatment levels for each component.

Post sizing — Timber posts are typically 125×125mm or 150×150mm hardwood, or 150mm diameter treated pine rounds. Post spacing is tighter than concrete sleeper walls — typically 1.2–1.8m — because timber is less rigid.

Design life — Timber walls have a shorter design life than concrete or masonry (typically 15–25 years vs 50+ years). We design for the appropriate durability class and advise on maintenance requirements.

Drainage — Drainage is even more critical for timber walls than concrete. Prolonged moisture contact accelerates timber degradation. We specify drainage systems that keep the timber as dry as possible while managing hydrostatic pressure.

Height limitations — We generally recommend timber only for walls up to 1.2m retained height. Above that, concrete sleeper or masonry systems are more cost-effective and durable. For taller walls, consider a concrete sleeper system.

What You Receive

Structural calculations to AS 4678, construction drawings specifying timber sizes, treatment levels, post spacing, footing details, drainage design, and engineer's certification for council.

Pricing

Timber retaining wall engineering from $600+GST. Most timber wall projects are on the lower end of our fee scale as they're typically shorter walls with simpler loading conditions.