Terracing transforms a challenging sloped yard into usable space by creating level platforms, or terraces, using retaining walls. This technique breaks a steep incline into gentle, manageable sections, mitigating erosion and improving drainage. This guide covers the entire process, from initial planning and material selection to construction and final planting.
Essential Planning and Permits
The first step involves accurately assessing the slope’s grade to determine the number and height of retaining walls needed. Use a line level or digital level app to calculate the vertical drop (rise) over a horizontal distance (run). This calculation ensures that no single wall exceeds a safe or permitted height.
Design must focus on the setback, which is the horizontal distance between the face of one wall and the base of the wall above it. Adequate setback provides usable space and prevents the upper wall’s weight from compromising the stability of the lower wall. Laying out the design with stakes and string helps visualize the final dimensions and confirm optimal placement.
Before breaking ground, check local zoning ordinances, as retaining walls are subject to specific building codes. Most municipalities require a building permit and often professional engineering consultation for walls exceeding 3 to 4 feet. Ignoring these regulations can lead to costly reconstruction or legal penalties.
Contact the national call-before-you-dig number, 811, several days before any excavation begins. This free service ensures that all underground utility lines, such as gas, water, and electrical conduits, are located and clearly marked. Digging without this step poses a significant safety hazard and risks severe damage to public infrastructure.
Choosing Terracing Materials
Engineered concrete masonry units (CMUs), or segmental retaining wall blocks, are popular for DIY terracing due to their interlocking design and uniform size. These blocks offer high durability and predictable installation, often relying on pins or lips for stability without requiring mortar. Pre-cast concrete options are typically the most straightforward and fastest method for homeowners.
Natural stone provides a classic aesthetic, but its complexity varies depending on whether it is dry-stacked or mortared. Dry-stacking requires careful stone selection for proper fit, while mortared walls require masonry skill and a secure foundation. Pressure-treated lumber, such as landscape timbers, can be used for a rustic or budget-conscious approach, but wood has a shorter lifespan and requires specialized anchoring.
Poured concrete offers the greatest strength and longevity, making it suitable for very tall or heavily loaded walls. However, it is the most labor-intensive and least DIY-friendly option, requiring formwork, precise mixing, and often professional installation. Selecting the right material balances aesthetic preference with structural performance and construction comfort level.
Building the Retaining Walls
Construction starts by excavating a trench for the wall’s foundation, or footing. This trench must be deep enough for the leveling pad and, in cold climates, should extend below the local frost line to prevent structural heaving. The base of this trench must be perfectly level along its entire length, as any deviation compromises the wall’s stability.
The foundation begins with a compacted layer of crushed stone, typically 6 to 8 inches deep, serving as the leveling pad. This granular base distributes the wall’s weight evenly and prevents settling, ensuring the first course of blocks remains stable. The first layer of blocks or timbers must be carefully placed onto this base, ensuring it is level both front-to-back (batter) and side-to-side.
Subsequent courses of material are laid following specifications, with joints staggered to lock the structure together. For segmental blocks, this involves placing connecting pins or utilizing the integrated lip mechanism to secure each layer. Treated lumber walls require long rebar or specialized spikes driven through the timbers into the underlying soil for anchorage.
The most important construction detail is managing hydrostatic pressure, the force exerted by water trapped behind the wall. Without proper drainage, this pressure will build up, causing the wall to bulge or fail. This necessitates installing a perforated drainpipe, often called a French drain, directly behind the base of the wall, positioned slightly above the leveling pad.
The drainpipe must be wrapped in a geotechnical filter fabric to prevent fine soil particles from clogging the perforations. The space immediately behind the wall, surrounding the pipe, should be backfilled with clean, coarse gravel to facilitate water movement. The filter fabric must extend up the back of the wall, separating the gravel drainage layer from the main soil mass.
Finally, the remaining space is filled with excavated soil, added in thin layers, or lifts, typically 6 to 8 inches deep at a time. Each lift must be carefully compacted using a plate compactor or hand tamper before the next layer is added. Proper compaction prevents future soil settlement and ensures the backfill material provides the necessary counterweight to the retaining wall.
Finishing the Terraces and Planting
Once the walls are complete and the backfill is settled, the new terraces are ready for soil amendment. Since excavated soil may be dense or nutrient-poor, blending in high-quality topsoil and organic compost is necessary to create a fertile planting medium. This preparation ensures the landscape beds will support robust plant growth and maximize water retention.
Planting choices should prioritize species with dense, fibrous root systems that help bind the soil and prevent surface erosion. Groundcovers and perennial shrubs are excellent choices for stabilizing the soil mass. Avoid planting large trees or woody ornamentals too close to the retaining wall, as their extensive root growth can exert pressure on the structure and compromise its integrity.
Long-term maintenance involves routinely inspecting the wall for signs of movement, such as bowing, leaning, or settling of the terrace surface. It is important to periodically check that the drainage system’s outlets remain clear of debris. Ensuring water can freely exit the system prevents the build-up of hydrostatic pressure, which is the primary cause of retaining wall failure.