For heights greater than 6 meters (20 feet), Counterfort Walls and Anchored Walls are the most suitable. Traditional gravity or cantilever walls become impractical at extreme heights due to excessive thickness and material costs.
Poured concrete retaining walls are the strongest and most durable option available. They offer versatility in design, as the concrete can be stamped, stained, veneered, or carved to mimic other materials like mortared stone.
The 1/3 rule is a general guideline for stability: About 1/3 of the wall's total height should be buried below ground. This helps the wall resist the pressure from soil and moisture behind it.
Counterfort retaining walls are used for heights beyond 6 m because they have counterforts (triangular-shaped supports) at intervals, which reduce bending moments and material usage.
Wood retaining walls come in all shapes and sizes, but the most common type is made from 4x4 or 6x6 posts stacked and fastened together. Another popular design is a post-and-panel style, where 4x or 6x posts support horizontally attached 2x boards, creating a strong and visually appealing structure.
A reinforced wall is constructed using either geogrid reinforcement or concrete backfill, both of which reinforce the structure. This reinforcement allows retaining walls to be built much higher than a gravity wall and support extra weight in addition to that of the retained soil.
Retaining Wall Height and Drainage Risk
Generally: Under 600mm: May get by with basic drainage if the soil is free-draining and the site is dry. 600mm–1.5m: Subsoil drainage is essential, even on small residential walls. 1.5m and over: Requires engineered plans, formal drainage designs, and consent.
Seven common mistakes when installing retaining wall blocks include poor base preparation, inadequate drainage, not using proper backfill, failing to compact soil, improper alignment of blocks, ignoring wall height limits, and neglecting to use geogrid reinforcement when needed.
If between 1.5-2 metres from boundary, maximum wall height 2 metres. If greater than 2 metres from boundary, maximum wall height 3 metres. If more than 600mm above or below ground level, are contained by a structural support.
Concrete retaining walls are usually considered the strongest due to their durability and ability to withstand heavy loads. They are highly popular for both residential and commercial properties, offering long-lasting support with minimal maintenance.
For DIYers and beginners, the easiest retaining wall is a stackable, interlocking concrete block wall. These modern blocks (such as Pavestone or Adbri Versawall) feature built-in rear lips or tongue-and-groove systems that automatically set the proper angle and stack flush without needing mortar, rebar, or heavy machinery.
What Are The Three Types Of Retaining Walls?
Engineers are required for retaining walls higher than 4 feet. If you need a retaining wall higher than 4 feet, you'll need to employ the expertise of an engineer. After all, it needs to be built with a solid foundation and support to ensure it can do its job without the risk of compromising its structural integrity.
Common causes include: Excessive Rainfall & Flooding: Saturated soils create hydrostatic pressure behind the wall, often leading to blowouts or bulging. Seismic Activity: Earthquakes can shift wall foundations and loosen soil behind the wall, causing total collapse.
Hydrostatic pressure and freeze‑thaw cycles act on any wall that holds back soil, no matter how low. Building codes also step in around 4 feet, where engineering and clear retaining wall drainage requirements are usually mandatory.
If you want to manage soil and slopes without building a traditional retaining wall, you can use landscaping techniques like terraced grading, riprap rock placement, or geogrid-reinforced vegetated slopes. These alternatives often blend naturally into your yard and are typically much easier and cheaper to install.
Foundation bearing (gravity case)
For the following simplified procedure, the “middle third rule” is applied, whereby the wall foundation is dimensioned so that the resultant vertical force acts through the “middle third” of the footing.
Retaining walls and slopes can collapse
Storms, floods, and earthquakes can produce landslides, causing sloped land and retaining walls to collapse and cause damage. Like any part of your house or property, retaining walls and some slopes need to be maintained.
Yes, a drain pipe is highly recommended for almost all retaining walls. Trapped water is the number one cause of wall failure. Without a pipe, water saturates the soil and creates "hydrostatic pressure" (heavy, expanding wet dirt), which can crack, bulge, or completely topple your wall.
The International Building Code (IBC) requires engineering design for any retaining wall 4 ft (1.21 m) or taller retaining soil and any retaining wall 2 ft (0.60 m) or greater retaining lateral loads (like buildings, streets, parking, etc.) in addition to soil.
For a French drain, the holes in your perforated pipe should face down (between the 5 and 7 o'clock position). This allows water that pools at the bottom of the gravel trench to easily rise up and enter the pipe through hydrostatic pressure, rather than waiting for the water level to submerge the entire pipe.
The most affordable and beginner-friendly retaining wall options are interlocking concrete blocks, treated timber, or stacked cinder blocks. These materials typically cost between $2 and $6 per block, making them ideal for DIY projects. Always ensure proper soil drainage and check local building codes for walls over 3 feet tall.
Diaphragm walls, crafted from reinforced concrete, find prominence in deep excavation projects and foundation support. On the other hand, retaining walls serve as barriers against lateral soil pressure when confronted with changes in ground elevation.
Disadvantages of Retaining Walls
Retaining walls require careful planning and engineering to ensure they are strong enough to hold back the soil. Another disadvantage of retaining walls is that they can be difficult to maintain. Retaining walls can be susceptible to erosion, cracking, and other types of damage.