Retaining Wall Calculator
SRW block, poured concrete, or timber-tie retaining-wall material + labor with IRC engineering-threshold warning, base stone, drain pipe, geogrid layers, and cap.
1.0 for 8-in block; 1.2 for 6-in
4-in perf pipe behind wall
0 for walls < 3 ft; 1–4 for taller
$50–80 typical
15–30 sf face / hr
Result
- Face area
- 120 sq ft
- Block count
- 120
- Base stone yd³
- 1.67
- Geogrid sq ft
- 240
- Block / wall cost
- $660
- Base stone
- $75
- Drain pipe
- $105
- Geogrid
- $288
- Cap
- $360
- Excavation
- $520
- Material total
- $2,008
- Labor
- 6.0 hr · $390
- Total installed
- $2,398
- Effective $ / sq ft face
- $20
This estimate is based on national average costs and may vary by region, project specifics, and market conditions. Use as a starting point for your bids.
Retaining wall pricing benchmarks
| Type | Installed $/sq ft face | Lifespan |
|---|---|---|
| SRW segmental block | $25–55 | 50+ years |
| Poured concrete | $40–75 | 50+ years |
| Timber tie (PT 6×6) | $20–35 | 15–25 years |
| Natural stone / boulder | $40–100+ | 50+ years |
The four cost drivers
- Face area: length × height drives the bulk of the material cost
- Excavation: trench for footing + backslope cut. $50–80/yd³ in most markets.
- Base + drainage: 6 in #57 stone + 4-in perf pipe + filter fabric. ~$15/LF installed.
- Reinforcement: geogrid layers for SRW > 3 ft, rebar for poured concrete. Code thresholds apply.
IRC + engineering thresholds
4 ft from footing-bottom to wall-top triggers engineered design in most jurisdictions. Add a surcharge (driveway, structure within H+1.5×H setback) and the threshold drops to 3 ft or even 2 ft. SRW manufacturer specs typically require geogrid reinforcement starting at 3 ft regardless of code — check the Allan Block / Versa-Lok engineered cross-section for the block you're using.
Frequently asked questions
When does a retaining wall need engineering?
IRC threshold: 4 ft from the bottom of the footing to the top of the wall typically triggers engineered design. Many jurisdictions are stricter (3 ft on slopes, 2 ft if surcharged by driveways or structures). For SRW blocks taller than 3 ft, manufacturer specs usually require geogrid reinforcement layers every 2 courses regardless of code.
SRW block vs poured concrete vs timber — installed cost?
SRW block (Allan Block, Versa-Lok): $25–55 per sq ft of face installed. Poured concrete: $40–75 per sq ft (formwork + rebar + concrete + finish). Timber tie (6×6 PT): $20–35 per sq ft but 15–25 year lifespan vs 50+ for SRW. Stone/boulder walls: highly variable, $40–100+ depending on stone source.
How thick a base do I need?
6 inches of compacted #57 stone over undisturbed subsoil is the standard for SRW walls under 4 ft. Trench width should be ~36 inches (12 in beyond face on each side) to allow proper compaction. Walls over 4 ft typically need a wider, deeper base — get the engineered drawing.
Do I always need a drain pipe behind the wall?
Yes for any wall holding water-retaining soil (clay, loam). 4-inch perforated drain pipe at the base, wrapped in filter fabric, daylighted to a low spot or storm drain. Without drainage, hydrostatic pressure builds behind the wall and pushes it over within 3-5 winters in freeze zones. Free-draining sandy soil sites can skip the pipe but always include filter fabric behind the wall.
How fast does an SRW crew build?
Experienced 3-person crew: 60-100 sq ft of face per day on a straight wall with good access. Curves, steps, and tight access drop this by half. Excavation + base prep is typically 1 day before the first course goes in. A 30 ft × 4 ft = 120 sq ft wall is a 2-3 day job including base.
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