Retaining Wall Timber

First gate: consent exemption is conditional

MBIE's Schedule 1 guidance describes an exemption for some retaining walls retaining no more than 1.5 m depth of ground where the wall does not support surcharge. A nearby driveway, building, steep slope or load can be surcharge. Exempt work must still comply with the Building Code and other legal requirements.

1. Measure retained depth, not only the exposed face.
2. Identify loads above and behind the wall.
3. Locate boundaries, services and neighbouring structures.
4. Ask the council/designer whether consent or resource rules apply.
5. Obtain geotechnical or engineering input appropriate to the site.

Water is a structural load

A wall without a reliable drainage path can retain water as well as soil. Design commonly considers free-draining backfill, filter fabric, subsoil drainage and a lawful outlet. Details must prevent fines clogging drainage while avoiding uncontrolled discharge onto neighbours or unstable ground.

• Confirm the outlet before excavation.
• Keep drainage zones clear during backfill.
• Do not substitute excavated clay for specified free-draining material.
• Provide surface-water control above the wall.
• Plan inspection before drainage and pole embedment are concealed.

Translate the engineered schedule without simplifying it

H5 is commonly associated with severe ground-contact retaining products, but the hazard class does not set pole diameter or spacing. A smaller H5 pole is not equivalent to the designed member. Treat supplier substitutions as design changes.

Excavation and delivery need one plan

WorkSafe's excavation guidance should inform hazard planning, especially around collapse, services, plant and access. Long wet poles are heavy; the delivery vehicle and lifting/unloading method need stable access outside unsafe excavation edges.

1. Mark services and exclusion zones.
2. Confirm truck route, turning and ground bearing.
3. Set an engineered storage/unload area away from the cut.
4. Sequence drainage aggregate and timber delivery to avoid rehandling.
5. Keep producer and treatment identification with the material.

A pre-design information pack

Useful engineering input includes a site plan, levels at the top and toe, photographs, boundary position, nearby buildings and driveways, drainage outlets, soil observations and known services. Record whether future fences, sheds or vehicle areas may add load. This reduces the risk of pricing a wall that later changes form.

• Retained height at several points, not one average.
• Length, corners, steps and end returns.
• Existing slips, seepage or cracking.
• Access for drilling/excavation equipment.
• Where excavated soil and imported drainage aggregate can be staged.

A neighbour's wall, shared boundary or diverted water may bring legal and coordination issues beyond building consent. Resolve them before excavation or placing an order that cannot be returned.

Estimate materials only after member spacing is supplied

Once a designer sets wall length and maximum pole centres, spaces = wall length / permitted centres and pole lines are generally spaces rounded up plus one, adjusted for corners and ends. This arithmetic does not choose the centres. Wall boards are then measured by actual course height and overlap/joint detail, with drainage and hardware on separate lines.