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Retaining walls: basics

Retaining walls are commonly used to level or retain slopes and give them a more vertical character. Generally, the more restricted or congested the site, the greater the need for retaining walls to provide usable space for landscape purposes.

Functional retaining walls are constructed for purely structural needs. For example, they can be used to level, retain, or terrace a sloping area; to maintain an existing grade around a tree or some other landscape feature you're trying to save; to allow a more abrupt change in grade than you can achieve with graded slopes; and to support a level area such as a patio or driveway.

Outdoor steps are modified human-scale retaining walls. Like outdoor steps, some retaining walls serve a purely functional purpose, and you may not be able to incorporate aesthetic considerations such as form, texture, color, shape, scale, and proportion.

Other retaining walls are used for visual effect in the landscape, and generally have several common characteristics. For example, they feature an informal shape and irregular placement of wall materials. They're less significant in size but more pronounced in visual character than functional retaining walls. They complement other landscape elements such as plants, paving and mulches. They're more compatible with human activity and can be adapted to many uses. They can be used as a bench wall, as a base for a fence, or an accent element in the landscape. And the materials used to build decorative retaining walls -- native stone, timbers and colored concrete bricks and blocks -- are chosen to provide the desired visual effect in the landscape.

The higher the retained slope, the more structural stability is required. Many times, critical structural requirements necessitate engineering a design that considers the length of slope, site-soil characteristics, the wall material used, construction space available and height of the wall. Complex structural walls require the design expertise of an experienced engineer. Many municipalities require that walls greater than four feet in height be designed by engineers. You'll need to verify this requirement with your municipality prior to planning construction of any major wall.