How to Build a Block Retaining Wall: Base, First Course, Drainage

Building a 25 ft × 3 ft block wall yourself: $1,945–$2,245 in block, stone, pipe and a compactor, 25–40 hours.

Before you start

Read the cost comparison first. A 25-foot, 3-foot block wall is about $2,095 in materials and rentals against $3,600 from a contractor — a $1,505 saving for 25–40 hours — and the timber version saves less because the timbers are most of the cost. What decides DIY here isn’t the money; it’s height and what’s above the wall.

The hard line: under 4 feet, lawn above it, no driveway, no slope rising behind it, no structure within a wall-height of it. That wall, in segmental block, is this guide. Anything else needs a permit and a stamped design and isn’t a homeowner project, whatever a video says.

What you need

Segmental block and caps for the square footage plus a buried course, crushed gravel for the base, clean 3/4-inch drainage stone, 4-inch perforated pipe with a sock, landscape fabric, construction adhesive, and marking paint. Tools: a plate compactor rental, a hand tamper, a 4-foot level and a torpedo level, mason’s line, a rubber mallet, a brick chisel and 3-lb hammer or an angle grinder with a diamond blade, and the shovel, mattock, wheelbarrow and rake you likely own. The priced list is on the cost page.

The three things that decide whether it lasts

The base. Six inches of compacted, level, crushed gravel and a buried first course. It’s a third of the labor and the whole foundation of the wall.

The first course. Every block level both ways, tight to the line. A quarter inch here is an inch at the top and a wave in the wall forever.

The drainage. Pipe at the bottom that goes somewhere, a foot of clean stone behind every course, fabric to keep the soil out. It’s the part nobody sees, the part cheap quotes skip, and the reason a wall built this way is still straight when a wall built without it has fallen over. The batter — the backward lean the blocks set — helps, but it doesn’t replace drainage.

Step by step

1. Check the rules, call 811, and lay it out

   Confirm the wall is under your city's permit height and has no driveway, slope or structure above it. Call 811 and wait for the marks. Stake the wall line and pull a string; measure the grade change at both ends so the wall's height is known before you order. Order block, caps, base gravel, drainage stone, pipe and fabric by the ton and the pallet, delivered as close to the wall as the truck can get.

2. Dig the trench

   Trench along the line, twice the block's depth wide and 6 inches plus one block height deep, level along its length — on a slope, step the trench in block-height increments. Pile the soil where it can go back as backfill; the excess goes to a low spot or gets hauled.

3. Build and compact the base

   Lay fabric in the trench if the soil is clay. Spread 3 inches of crushed gravel, run the plate compactor over it in two passes, add the next 3 inches, compact again. Screed the surface flat and level with a straight board; check with a 4-foot level along and across. This surface is the wall.

4. Set the first course

   Starting at the lowest or most visible end, set each block on the base, tap it down with the mallet, and level it front-to-back and side-to-side — add or scrape gravel under it as needed. Keep it tight to the line and to the block before it. Go slowly; this course takes as long as the next three.

5. Lay the drain pipe

   Set the perforated pipe on the base behind the first course, holes down, in a sock, sloped toward its outlet. Run it out to daylight at the end of the wall or to a drain. Cover it with clean stone.

6. Stack the courses, stone behind each

   Sweep each course before the next. Stagger the joints by half a block; the lip or pins set the batter. After each course, add clean stone behind it to the height of that course and lightly compact it, then backfill the soil behind the stone in a 6-inch lift and compact that too. Fabric between the stone and the soil keeps fines out. Split blocks with the chisel or grinder at ends and corners.

7. Cap it

   Stop the block a cap's height below the finished grade above. Pull fabric over the top of the stone. Glue the caps with a bead of construction adhesive on each block, overhanging the face by an inch, tight to each other; cut caps at corners and curves.

8. Finish the grade

   Bring the backfill up to 6 inches below the cap, then topsoil, sloped slightly away from the wall so surface water doesn't run behind it. Seed or sod. Check the drain outlet after the first heavy rain.

What would this cost you? The retaining wall calculator prices the DIY version with the tools you already own and a value on your time, next to a pro quote.