Introduction
This case study is hypothetical and illustrative — a realistic but fictional project assembled to show how the estimating, budgeting, and build sequence fit together on a typical residential wall. The numbers use the standard planning figures applied across this guide series; no real client, contractor, or site is described.
The project: a homeowner (“the builder” below) replaces a failing timber landscape wall with a segmental block wall along a garden bed — 20 ft (6.1 m) long, 3 ft (0.91 m) exposed height, straight run, level grade, good access. Quantities throughout come from the Retaining Wall Calculator using the formulas derived in the formula guide.
The Situation (Hypothetical)
The existing timber wall is leaning after a decade; the bed behind it has settled. The builder wants a permanent segmental wall at the same 3 ft exposed height — safely under the 4 ft (1.2 m) engineering trigger, confirmed with a quick call to the local building authority (no permit required at this height locally, but requirements vary — see the code compliance guide). Utility locates are called in and clear. The plan: DIY over two weekends with one helper.
Why segmental block instead of rebuilding in timber? The original timber wall lasted about ten years before rot and lean set in — a concrete segmental system, properly drained, is a multi-decade wall. The builder also chose to keep the exact 3 ft exposed height rather than gaining a few inches of bed depth, deliberately staying well clear of the 4 ft threshold where engineering and permits would erase the DIY cost advantage. That height discipline is itself one of the project’s key decisions.
The Estimate
Measurements: L = 20 ft (6.096 m), H = 3 ft (0.914 m), straight run, level grade. Planning figures: 1.0 ft² (0.0929 m²) per block, 8% block waste, 12 in (30 cm) caps with 5%, 18 in × 6 in base trench, 12 in drainage column, 10% aggregate allowance.
| Item | Calculation | Result |
|---|---|---|
| Buried depth | max(36/8, 6 in) | 6 in (0.15 m) |
| Total wall height | 3 ft + 0.5 ft | 3.5 ft (1.07 m) |
| Face blocks | 20 × 3.5 ÷ 1.0 × 1.08 → up | 76 blocks |
| Cap stones | 20 ÷ 1 × 1.05 → up | 21 caps |
| Base gravel | 20 × 1.5 × 0.5 = 15 ft³ ÷ 27 × 1.10 | 0.61 yd³ (0.47 m³) |
| Drainage aggregate | 20 × 3 × 1 = 60 ft³ ÷ 27 × 1.10 | 2.44 yd³ (1.87 m³) |
| Drain pipe | wall length + outlet | 20 ft (6.1 m) + outlet |
Metric verification: 6.096 × 1.067 = 6.50 m² ÷ 0.0929 = 70.0 × 1.08 → 76 blocks ✓; base 6.096 × 0.457 × 0.152 = 0.425 m³ × 1.10 → 0.47 m³ ✓; drainage 6.096 × 0.914 × 0.305 = 1.70 m³ × 1.10 → 1.87 m³ ✓.
The Budget (Hypothetical Planning Prices)
Using mid-range planning prices (regional variation is wide — the cost guide has the full ranges):
- 76 blocks × $4.50 ≈ $342
- 21 caps × $6 ≈ $126
- Aggregate ≈ 4.5 tons × $45/ton ≈ $203
- Pipe, fabric, adhesive, fittings ≈ $75
- Delivery (one combined load) ≈ $75
- Plate compactor rental, 2 days ≈ $150
Illustrative DIY total: ≈ $970. A pro-installed equivalent at $35–$55 per sq ft of face (60 sq ft) would run $2,100–$3,300 — the DIY saving of roughly $1,100–$2,300 represents two weekends of labor for two people. The builder’s decision framework is the DIY vs pro guide.
The Build Sequence (Illustrative)
Weekend 1 — demolition and base. Remove the old timber wall and excavate the trench: 18 in wide, ~12 in deep (6 in base + 6 in burial). Compact the subgrade, place 6 in of crusher run in 2–3 in lifts with the plate compactor, screed level. Lay the perforated pipe at what will be the base of the drainage column, routed to a daylight outlet downhill. Set and level the first (buried) course — the slowest, most careful work of the project.
Weekend 2 — courses, drainage, caps. Stack courses with half-block stagger, filling the 12 in drainage column with clean stone behind each course before setting the next, wrapping the soil side with filter fabric. Compact backfill in 6–8 in lifts as the wall rises. Dry-fit caps along the top, trim as needed, then glue with concrete adhesive. Finish-grade topsoil to drain away from the wall face.
The techniques at each stage are detailed in the pro tips guide; the error watch-list is covered in the common mistakes guide.
What Could Go Differently (Lessons, Still Hypothetical)
- If the grade had sloped: the wall would be estimated in sections, and the tall end would need its own drainage height — the sectioning technique is covered in the estimating guide.
- If the height had been 4+ ft: the project would stop being DIY — engineered drawings, geogrid schedule, permits, and likely a contractor.
- If access had been tight: the ~4.5 tons of aggregate moving by wheelbarrow over a long carry would have tipped the decision toward hiring the labor out.
- If the soil had been soft clay: the base would go deeper (toward the 6 in end or beyond per engineering judgment) and the budget would carry contingency.
Related Guides
- Complete Guide — the estimating overview this project follows.
- Cost Guide — the price ranges behind the illustrative budget.
- Pro Tips — the build techniques used in the sequence above.
- Pre-Build Checklist — the punch list this project would start from.
- DIY vs Pro — the decision framework applied here.
Get Your Number
This hypothetical project shows the full arc: measure, estimate, budget, build — with the calculator handling the arithmetic at the center. Your wall’s numbers will differ, but the sequence doesn’t. Run your dimensions through the Retaining Wall Calculator, price the quantities locally, confirm permits with your building authority, and build the invisible parts (base, drainage, compaction) as carefully as the visible ones.
Disclaimer: This case study is hypothetical and illustrative — not a real project. All costs are illustrative planning figures with wide regional variation. Calculator results are planning estimates. Verify quantities with your supplier and consult a licensed engineer or your local building authority for structural design and permits — walls over 4 ft (1.2 m) typically require engineering and permits.
