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How to Build a Retaining Wall

A retaining wall turns a slope into flat, usable yard, and the most popular DIY type is stacked segmental block. Under about 4 ft it’s a strong weekend project; taller than that (or with a slope or driveway above it) needs an engineered design. The whole wall depends on a level base and real drainage. Tap “Add to my materials list” as you go.

DifficultyIntermediate
TimeA weekend or two
Cost$$ (block + gravel)
PermitsOften above ~3–4 ft
Permits & safety: Call 811 before digging. Many areas require a permit for walls over about 3–4 ft, and an engineered design is required above ~4 ft or whenever there’s a slope, driveway, or other load above the wall. Stay under 4 ft for a DIY gravity wall.
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1Call 811 and excavate the base trench

Mark utilities, then dig a trench wide enough for the block plus ~12” of gravel backfill behind it, and deep enough for a 6” base plus the buried bottom course. The calculator gives the dirt to dig and haul.

Dirt to remove
22.2 cu yd
Dig area
600 sq ft12" deep
In-ground volume
22.2 cu yd
Loose (haul) volume
27.8 cu yd+25% soil swell once dug
Truckloads
3~12 CY per dump truck
Haul + disposal (est.)
$556~$20/CY (varies by area)

2Build a compacted gravel leveling pad

Fill the trench with about 6” of crushed gravel/road base (not sand) and compact it in 2–3” layers, finishing dead flat to within ~1⁄8” over 4 ft. The calculator gives base gravel by the ton or yard.

Retaining wall drainage and batter Step blocks back — batter ≈ 1″ per ft Retained soil Filter fabric Free-draininggravel backfill Perforated drain pipeweeps water to daylight Bury bottom course on a compacted gravel leveling pad
Retaining-wall drainage — gravel backfill, filter fabric, and a perforated drain pipe at the base carry water out before it can push the wall over. Step each course back (batter) and bury the first course.
Gravel needed
10.0 tons
Area
600 sq ftat 4" deep
Gravel needed
10.0 tons7.41 cubic yards
Delivered cost (est.)
$450~$45/ton crushed gravel

3Set and level the buried first course

Lay the bottom course on the pad and level every block front-to-back and side-to-side. Bury it the greater of 10% of the wall height or 6” (about 5” on a 4-ft wall). Time spent perfecting this course pays off in every course above.

4Add drainage and backfill

Set a 4” perforated drain pipe behind the base, sloped to daylight, and backfill with at least 12” of clean free-draining gravel, separated from the native soil with filter fabric. Without drainage, water pressure is the #1 cause of wall failure.

5Stack with batter, compact, and cap

Sweep each course clean and stack so the blocks step back (batter) per the block’s lip or pins, compacting backfill in lifts no thicker than 8”. Add geogrid every 2–3 courses if your wall or design calls for it, then glue on the cap course. The calculator gives block and cap counts.

You'll need
90 blocks
Wall area
60 sq ft20' long × 3' high
Wall blocks
9016" long × 6" high × 10" deep
Cap blocks
15~16" units
Gravel base / backfill
1.0 tons6"-deep leveling base + drainage backfill
Block cost (est.)
$450~$5/block material
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Frequently asked questions

How tall a retaining wall can I build myself?
Up to about 3–4 ft as a gravity wall. Above ~4 ft, or with a slope or driveway above it, you need an engineered design.
How deep should the base be?
A 6” compacted gravel leveling pad in a trench, with the first course buried the greater of 10% of wall height or 6” below grade.
Why does a retaining wall need gravel and a drain pipe?
Water building up behind the wall creates pressure that pushes it over. A column of free-draining gravel and a perforated pipe to daylight carry that water away.
Do I need geogrid?
Most block makers require geogrid (a soil reinforcement grid) above about 3 ft, placed every 2–3 courses. Below that, a gravity wall usually suffices.

Calculators in this project

Excavation
Cubic yards of dirt to dig and haul, plus truckloads.
Gravel
How much gravel you need for a driveway, path, or base — in tons and cubic yards.
Retaining Wall
Blocks (real sizes or custom), poured concrete, timber, or stone — with caps and base.
Paver
Pavers (any size), gravel base and sand for a patio or walkway.
Brick
Brick count and mortar bags for a wall.

Sources & references