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Modular Block Retaining Wall Systems

Segmental retaining walls employ interlocking concrete units that tie back into the earth to efficiently resist loads.

Photo of a modular block retaining wall system used in a residential landscape.

Modular block, or segmental, retaining walls employ interlocking concrete units that tie-back into the earth to efficiently resist loads. These pre-engineered modular systems are an attractive, economical, and durable alternative to stone or poured concrete retaining walls. The inherent design flexibility can accommodate a wide variety of site constraints, project sizes, and aesthetic preferences.

Individual, usually identical, precast concrete units either interlock, offset stack, or are placed structurally independent of each other and anchored into the backfill. These independent tier systems are advantageous for seismic areas. The components of a complete system can include foundation soil; leveling pad; precast concrete units of high-strength concrete; shear pins if units don't interlock; multiple-depth walls or additional soil reinforcement such as geotextile, welded wire fabric, or dead-man anchors if the wall is over a certain height; retained soil; and drainage fill. Some systems have relatively shallow units while others have units with a tail for deep embedment for taller or more vertical walls (walls are never perfectly vertical). The soil reinforcement consists of horizontal layers that extend into the backfill.

Being gravity structures, these systems rely on their own weight and coherent mass to resist overturn and sliding forces. The segmental nature affords the wall a permeability to relieve hydrostatic pressure, so less material is required for resistance. Because they are considered flexible structures, the footings usually need not reach the frost line. Some systems allow for landscaping of the wall between tiers (depending on site conditions), while others are designed as structural frames to be covered with landscaping.

These systems have been installed all over the U.S.; distributor locations vary per manufacturer.


Modular Block systems off a cheaper alternative to having a concrete retaining wall poured, while still performing the same function.


Installation can be done by the homeowner in many situations. Some onsite setup is probably necessary. Additional soil reinforcement will be required for very steep walls or those over 5' to 6' in height. If a wall has additional loads such as sloping backfills or live loads, has a poor foundation, or exceeds the manufacturer's recommended height, a professional engineer should be consulted.

Modular retaining walls are generally between $5 and $10 per square foot, for a one foot deep wall. Price will vary depending on the type of block and color used.

Not Applicable

Some local building codes require a professional engineer to design the wall if over a certain height.

Not Applicable

These systems usually require less excavation than poured-in-place walls, and on-site soils can often be used. They require no heavy equipment, mortar or formwork, and usually can be constructed by hand. This affords flexibility in construction scheduling. Proper backfilling and grading for base tier is fairly critical. These systems can also be overlaid onto existing older retaining walls.

Not Applicable

These systems allow for some design flexibility, such as curved walls, and construction is generally faster than poured-in-place concrete or stone walls. Site conditions have a major impact on costs. Installed costs are usually less than poured-in-place and especially stone walls. Controlled manufacturing conditions ensure a durable, damage-resistant product. Maintenance is negligible as there is no mortar to repoint, and the flexible systems generally eliminate cracking.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the NAHB Research Center. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.