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Calculate materials needed for your retaining wall project. Get accurate estimates for blocks, gravel, drainage, and geogrid reinforcement based on your wall dimensions and block type.
Setback angle increases stability but requires more blocks
Finishing blocks for the top of the wall
Perforated pipe for water management (recommended)
Reinforcement layers every 2 ft (required for walls >4 ft)
0.0 per course × 0.0 courses
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A retaining wall is a structure designed to hold back soil and prevent erosion on sloped properties. These walls resist lateral soil pressure and create usable flat spaces in hilly terrain.
Retaining walls serve multiple purposes:
Calculate the number of blocks needed using these formulas:
Blocks per course = (Length × 12) / Block width
Number of courses = Height / (Block height / 12)
Total blocks = Blocks per course × Courses
Note: Add 5% per 6° of setback angle for angled walls. Always round up and add 5-10% extra for waste and cuts.
Wall: 20 ft long, 3 ft high
Block: Standard 12×8×4
Blocks per course = (20 × 12) / 12 = 20 blocks
Courses = 3 / (4 / 12) = 9 courses
Total = 20 × 9 = 180 blocks
With 6° setback: 180 × 1.05 = 189 blocks
| Block Type | Dimensions | Face Width | Face Height | Best For |
|---|---|---|---|---|
| Standard Block | 12×8×4 in | 12 inches | 4 inches | Low walls, garden beds |
| Large Block | 18×12×6 in | 18 inches | 6 inches | Faster installation, bigger projects |
| Versa-Lok | 16×12×6 in | 16 inches | 6 inches | Commercial grade, tall walls |
Block weights range from 25-75 lbs depending on size. Consider equipment rental for large projects.
Proper drainage is the most important factor in retaining wall longevity. Water buildup behind the wall creates hydrostatic pressure that can cause failure.
Never skip drainage to save money. It costs far more to rebuild a failed wall.
Geogrid is a mesh fabric that reinforces the soil behind retaining walls. It's essential for walls over 4 feet and recommended for walls 3-4 feet.
Geogrid layers are placed every 2 feet vertically, extending back into the soil at least as far as the wall is tall. The grid interlocks with soil particles, creating a reinforced mass.
Installation: Place geogrid on each course, extend back into fill, cover with 6 inches of gravel, then add next block course.
| Wall Height | Geogrid |
|---|---|
| Under 3 ft | Not required |
| 3-4 ft | Recommended |
| Over 4 ft | Required |
Geogrid costs $0.50-2.00 per square foot but can double the wall's load-bearing capacity.
Safe for DIY. No geogrid required. May not need permits in most areas.
Advanced DIY. Use geogrid. Check local permit requirements. Consider professional consultation.
Requires engineering. Permits mandatory. Geogrid essential. Strongly recommend professional installation.
For safety and code compliance, limit DIY retaining walls to 3-4 feet maximum. Walls over 4 feet typically require engineering stamps, permits, and professional installation. In some jurisdictions, the limit is even lower.
Water buildup behind a retaining wall creates hydrostatic pressure that can exceed the wall's design capacity. This pressure can cause walls to bulge, lean, crack, or completely fail. Proper drainage (gravel backfill + perforated pipe) eliminates this pressure.
Geogrid is a synthetic mesh fabric that reinforces soil behind the wall. Install layers every 2 feet for walls over 4 feet tall. It extends back into the soil, interlocking with fill material to create a reinforced mass that helps resist lateral soil pressure.
Setback angle is the backward lean of the wall (typically 6-12 degrees). This lean increases stability by directing weight into the slope and reducing forward pressure. It also creates a natural look but requires slightly more blocks since each course is offset.
Bury the base course below frost depth for your region (check local codes). Use well-draining gravel backfill and install proper drainage pipes. Frost heave occurs when water freezes and expands, so eliminating water prevents the problem.
Most municipalities require permits for walls over 3-4 feet. Some require permits for any wall. Walls near property lines often have additional restrictions. Always check with your local building department before starting construction.
Order 5-10% extra blocks to account for cuts, damage, and future repairs. For gravel, add 10-15% for settling and compaction. It's better to have extra than to delay the project for another delivery.
Yes, but the base must be level. Use step-downs (terracing the base course) to follow the slope while keeping each section level. This is more complex than a level installation and may require professional help for proper execution.
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