Retaining wall cost

A retaining wall costs $20 to $55 per square foot of exposed wall face, typically around $35. A 40 foot long wall standing 4 feet high is 160 square feet of face, so $3,200 to $8,800.

The measurement catches everyone. A retaining wall is priced by length times height, not by length alone, because doubling the height more than doubles the work: the wall gets thicker, the base gets deeper, and above a certain point it needs an engineer.

Cost by material

Material	Per square foot of face	Notes
Treated timber	$15 to $30	Cheapest, 15 to 20 year life
Segmental concrete block	$20 to $55	The default, no mortar, self-draining
Poured concrete	$25 to $55	Strongest, needs forms and cure time
Stacked boulders	$25 to $50	Needs machine access
Natural stone, dry laid	$35 to $80	Slowest to build, best looking
Brick	$20 to $40	Usually veneer over block

Segmental block is what most residential walls are, and for good reason: the units lock together, they tolerate ground movement, and they need no mortar and no cure time.

Cost by wall size

Segmental block at $35 per square foot:

Wall	Face area	Typical
20 ft long, 3 ft high	60 sq ft	$1,200 to $3,300
40 ft long, 3 ft high	120 sq ft	$2,400 to $6,600
40 ft long, 4 ft high	160 sq ft	$3,200 to $8,800
60 ft long, 5 ft high	300 sq ft	$6,000 to $16,500
60 ft long, 8 ft high	480 sq ft	$14,000 to $35,000

The last row is not simply proportional. Past about 4 feet, walls need geogrid reinforcement extending back into the slope, engineering, and usually a permit. The price per square foot rises with height rather than staying flat.

Four feet is the line

Almost every jurisdiction requires a permit and an engineer's design for walls above 3 or 4 feet, measured from the bottom of the footing rather than from the ground you see.

This is not bureaucracy. A 4 foot wall retaining saturated clay is holding back several tons per linear foot, and the failure mode is the whole wall going over at once. Walls fail after heavy rain, which is when the soil behind them is heaviest and when someone is least likely to be watching.

Two ways people get caught: building a wall at 3 feet 11 inches to avoid the permit, then finding the footing depth put it over the line. And building two 3 foot walls in a terrace, which counts as one taller wall unless they are separated by a horizontal distance the code specifies.

A stone retaining wall holding back planted ground — The load on a wall is soil plus water. Remove the water and the load drops sharply, which is why the drain pipe behind it is not the place to save money.

Drainage is what keeps it standing

The load on a retaining wall is soil plus water. Remove the water and the load drops by a large fraction.

A correct wall has:

A compacted gravel base below frost depth
The first course buried, typically one course or a tenth of the wall height
Clean drainage stone directly behind the wall, 12 inches deep
A perforated drain pipe at the base, sloped, with somewhere to daylight
Geotextile fabric separating the drainage stone from the backfill soil
Backfill compacted in lifts, not dumped
Geogrid reinforcement into the slope on anything above about 4 feet

The drain pipe is where cheap quotes save money, and it is the reason walls fail. Ask where the water exits. If nobody can answer, the pipe either does not exist or goes nowhere.

Terracing as an alternative

Two 3 foot walls with a planted bench between them frequently cost less than one 6 foot wall, and they usually avoid the engineering requirement. They also look better on most slopes and give you somewhere to plant.

The catch is the horizontal separation: codes specify a minimum distance between terraced walls, often twice the height of the lower wall, before they stop being treated as a single tall wall. Below that distance you are back to engineering.

What adds to the bill

Excavation and soil disposal: $50 to $150 per cubic yard removed
Difficult access, where everything is barrowed by hand: add 25% to 50%
Steps built into the wall: $150 to $400 per step
A cap course: $10 to $25 per linear foot
Engineering and drawings: $500 to $2,500
Permit: $150 to $800
Removing an existing failed wall: $10 to $30 per square foot of face

Frequently asked questions

How long does a retaining wall last?

Segmental block and poured concrete, 50 years or more with proper drainage. Treated timber, 15 to 20 years, because it is in permanent contact with wet soil. Dry-laid stone, effectively indefinitely.

Can I build one myself?

Under 3 feet, on flat access, yes: it is heavy work and the technique is straightforward. Above that, no. The consequence of a wall failing is not cosmetic, and homeowner-built tall walls are a recognised category of failure.

My wall is leaning. Can it be fixed?

Sometimes. Slight leaning on a low wall can be corrected by rebuilding the top courses and fixing the drainage. A wall bulging in the middle or leaning more than a few degrees is failing structurally and needs to come down and be rebuilt. Adding to the top of a leaning wall makes it worse.

Does it need a footing?

A segmental block wall sits on a compacted gravel base rather than a concrete footing, and the base must go below the frost line. Poured concrete and mortared walls need a proper concrete footing.

Will it stop my basement flooding?

Only if water flowing down a slope is the cause. A retaining wall redirects surface water and holds soil; it does nothing about groundwater or a failed foundation drain. Diagnose the cause before spending on the wrong fix.