Retaining Wall Footings: Depth, Width, and Design Requirements

Retaining Wall Footings Explained

The footing is the foundation of every retaining wall. It transfers the forces acting on the wall into the ground, preventing movement, tilting, and failure. Understanding footing requirements is essential whether you are building a small garden wall or a large structural wall. This guide covers footing depth, width, reinforcement, and design requirements for retaining walls in Melbourne and across Victoria.

Why Footings Matter

A retaining wall resists lateral earth pressure, which tries to push the wall over or slide it forward. The footing provides the resistance by anchoring the wall into the ground. An undersized or poorly constructed footing is the most common cause of retaining wall failure. Symptoms of footing failure include wall leaning, cracking, separation at joints, and ground heaving in front of the wall.

Footing Types for Retaining Walls

Strip Footings

Strip footings are continuous concrete footings running the length of the wall. They are commonly used for concrete block walls, masonry walls, and some stone walls. The footing width and depth are determined by the wall height, soil bearing capacity, and loads. A typical strip footing for a one-metre-high block wall is 400mm to 600mm wide and 300mm to 450mm deep, reinforced with steel bars.

Pier Footings

Pier footings are individual concrete pads or bored piers at each post location. They are the standard footing type for concrete sleeper walls and timber sleeper walls. Each steel or timber post is embedded in a concrete pier, typically 300mm to 450mm in diameter and 600mm to 1200mm deep, depending on wall height and engineering requirements.

Gravity Footings

Gravity walls such as boulder and gabion walls use their own mass as the footing. The base course is typically wider than the upper courses, with the base sitting on a compacted gravel pad. No reinforced concrete footing is needed for many low gravity walls, though a structural engineer should confirm this for walls over one metre.

Footing Depth Guidelines

Footing depth depends on several factors. Below are general guidelines, but always follow your engineer’s specifications:

• Walls up to 600mm high: Footing depth of 300mm to 400mm is typical for lightweight walls on stable soil
• Walls 600mm to 1m high: Footing depth of 400mm to 600mm, with concrete pier footings typically 600mm to 800mm deep for post-and-sleeper walls
• Walls 1m to 1.5m high: Footing depth of 600mm to 900mm, with pier footings often 900mm to 1200mm deep. Engineering is mandatory at this height in Victoria
• Walls over 1.5m high: Footing depth of 900mm or more as specified by your engineer, based on soil conditions and loads

Footing Width Guidelines

For strip footings, the width is typically 1.5 to 2 times the wall thickness. For example, a 200mm wide block wall requires a footing at least 400mm to 500mm wide. Engineers may specify wider footings in weaker soils or for taller walls. For pier footings, a diameter of 300mm to 450mm is standard for most residential retaining walls.

Reinforcement Requirements

Most retaining wall footings require steel reinforcement to resist bending and cracking. Common reinforcement includes:

• Strip footings: Two or three N12 bars running longitudinally, with N12 ligatures at 300mm to 600mm centres
• Pier footings: N12 or N16 starter bars extending up from the pier into the wall, with ligatures as specified
• Slab footings (for heavy walls): Steel mesh (SL72 or SL82) or bar reinforcement in both directions

Soil Conditions and Footing Design

Melbourne’s diverse soil conditions significantly affect footing requirements. Reactive clay soils, common across Melbourne’s eastern and northern suburbs, expand and contract with moisture changes, placing additional stress on footings. Sandy soils in bayside areas offer good drainage but may have lower bearing capacity. Fill soils require special consideration as they may not provide adequate support without compaction or piling.

If you are unsure about your soil conditions, a geotechnical report provides the information your engineer needs to design appropriate footings. Visit our council approval guide for more on permit requirements related to footing inspections.

Get Expert Footing Design

Footing design is not an area to cut corners. We connect you with licensed retaining wall builders who work with experienced structural engineers to ensure your wall’s footings are correctly designed and constructed for Melbourne’s conditions. Find a licensed builder to get your retaining wall project started on the right foundation.