Build Strong Walls with Precision

Retaining Walls: Structural Engineering and Drainage

Retaining walls are a completely different beast compared to standard brick or block walls. Their primary job is to hold back soil, which means they must resist immense lateral earth pressure and hydrostatic pressure from water.

1. The Critical Role of Drainage

The number one cause of retaining wall failure is poor drainage. When soil becomes saturated, its weight and pressure increase dramatically. Every retaining wall must have a drainage system behind it. This typically consists of a layer of clean gravel (washed stone) and a perforated drainage pipe (French drain) at the base.

Additionally, the wall itself must be permeable or have weep holes to allow water to escape. Using a geotextile fabric between the soil and gravel prevents the drain from clogging with fine soil particles. Our Retaining Wall Calculator helps you estimate the gravel and block quantities required.

2. Battered Walls (The Lean-Back)

In traditional masonry retaining walls, the wall is built with a slight "batter" (a lean back toward the soil). This shifts the center of gravity of the wall, making it more stable against overturning. The wall also needs a substantial concrete footing that extends below the frost line.

3. Geogrid Reinforcement

For walls higher than 3 to 4 feet, a simple gravity wall may not be enough. Modern segmental retaining walls use geogrid—a strong plastic mesh laid horizontally between the block courses and extending back into the soil. This reinforces the soil mass, essentially turning the soil into a larger, stable block that holds the wall in place.

Foundations for Masonry Walls

Brick and block walls are incredibly heavy. A standard 100mm concrete block wall weighs roughly 150 kg per square meter (or 30 lbs per square foot). This load must be transferred to stable ground.

The foundation (footing) for a masonry wall must be wider than the wall itself, typically extending 100mm to 200mm (4 to 8 inches) beyond each side. It must be poured using concrete (typically 2500 to 3000 PSI) and must extend below the local frost line to prevent frost heave from cracking the wall. For calculating the concrete volume for your foundation, use our Concrete Calculator.

Weathering and Efflorescence

If you have ever seen a white, powdery stain on a brick wall, you have seen efflorescence. This is caused by water-soluble salts migrating to the surface of the masonry and crystallizing as the water evaporates.

While usually not structurally damaging, it is unsightly. The best way to prevent it is to ensure good detailing (proper flashing, weepholes, and copings) to prevent water from entering the masonry in the first place. Applying a breathable water repellent after the wall has cured can also help.