Hillside and terraced retaining wall planning

Treat each terrace as a wall—and the group as one system

A stepped wall and a terraced wall are not the same takeoff. A stepped wall is one wall whose exposed height or base elevation changes along its run. A terraced system has two or more walls at different elevations. Make a separate material schedule for every tier, even when the tiers use the same block.

Do not assume the walls act independently because they are drawn as separate rows. Manufacturer guidance explains that tiered walls can interact and that the whole site—including soils, slopes above and below, water and nearby loads—can control performance. A material calculator cannot establish slope stability or safe terrace spacing.

Record a measured section for every tier

Start from a surveyed or otherwise project-approved layout. Give each tier a stable name such as lower, middle or upper. Record the baseline or reference arc used for its length, the bottom and top elevations, exposed height, cap line, returns, corners and every change in height. Keep the horizontal distance between tiers as a measured layout fact—not as a spacing recommendation.

Also record slopes above and below the system, driveways or other loads, drainage paths, outlets, utilities, access limits and the product selected. Those observations belong in the project handoff because they may affect design; they are not inputs from which this guide calculates structural requirements.

Calculate each tier and each height change separately

For a straight, uniform section, round units per course and exposed courses upward, then add only the buried courses shown for that section. Apply the chosen cutting or breakage allowance after calculating the net units. If height or embedment changes, split the tier into sections instead of multiplying one average height across the whole run.

The worked example uses 16-inch-long × 6-inch-high units, one buried course and a 10% allowance. The lower tier is 30 feet long and 3 feet exposed: 23 units per course × 7 total courses = 161 net, or 178 after allowance. The upper tier is 24 feet long and 2 feet exposed: 18 units per course × 5 total courses = 90 net, or 99 after allowance.

The face-unit purchasing subtotal is 277, but keep the 178- and 99-unit schedules separate. The sum does not select tier spacing, buried depth, reinforcement, drainage or a suitable wall system.

For each tier section:
Units per course = ceil(section length ÷ installed unit length)
Total courses = ceil(exposed height ÷ installed unit height) + plan-specified buried courses
Order units = ceil(units per course × total courses × (1 + allowance ÷ 100))

Measure curved tiers on one consistent reference line

Measure a curved run along the same reference line used for the unit’s installed coverage. Record the radius and central angle only when the layout actually follows a constant arc. Do not substitute the shorter straight chord or combine arcs with different radii into one entry.

The curved calculator converts one radius and angle to arc length. It does not check minimum product radius, course-by-course setback, tapered-unit gaps, cap cuts or reinforcement details at curves. Split compound curves into documented arcs and obtain the selected system’s layout details.

Tiered retaining wall spacing: what the manufacturer publishes

Allan Block’s Technical Sheet 1297, published in 1997 and reread October 26, 2026, describes separation of at least twice the lower wall’s height as its conservative guideline for two walls acting independently. The note is expressly for Allan Block products. It also discusses closer tiers, slopes and more complex systems that need further stability analysis.

That published ratio is context for a design discussion, not a national code, a safe-spacing output from this calculator or a substitute for site assessment. Soil, water, slopes, loading, wall geometry and the selected system still need project-specific review. Allan Block’s terraced-wall case study illustrates why the whole hillside can require global stability analysis.

Have the project professional establish tier interaction, separation, foundation, reinforcement and drainage details before the quantity takeoff. Check local permit requirements separately; an approval-height exemption does not establish safe tier spacing.

Coordinate drainage, excavation and overlapping quantities

Keep base aggregate, drainage stone, core fill, pipe, fabric and plan-specified reinforcement separate by tier. Water from an upper slope or wall must not be assumed to disappear between tiers. Record the actual collection, conveyance and lawful outlet details supplied for the project.

Rectangular calculator volumes can overlap where excavations, stone zones or reinforcement areas cross. Do not simply add overlapping prisms or double-count shared pipe. Mark overlaps on the section drawing and have the supplier or project professional reconcile them before the purchase order.

Review the tier schedules before requesting quotes

Issue the section drawing and all tier schedules together, but show subtotals for each tier and height section. That makes revisions traceable and helps the supplier keep standard units, corners, caps, aggregate and reinforcement attached to the correct wall.

Before ordering, reconcile each schedule against the current product data, approved details and real package sizes. Record who is responsible for survey control, excavation steps, drainage outlets, engineering or other design review, permits, inspections and field changes.

• Every tier has a name, elevations and a measured reference line.
• Changing heights, straight runs and arcs have separate takeoff sections.
• Buried courses and reinforcement come from the project details, not a generic threshold.
• Tier offsets remain measured facts; no calculator result is labeled as safe spacing.
• Drainage routes and overlapping excavation or material zones are reconciled.
• Special units, package rounding, exclusions and responsible parties are written on the quote.