Most home retaining walls don't sit on a concrete footing. A segmental block wall goes on a compacted gravel base with 12 inches of drainage stone behind it, and geogrid once it gets tall. Poured concrete walls need a reinforced footing and a drain. In Duluth, walls over 4 feet, footing included, need a permit and an engineer.
Do retaining walls need footings?
Every retaining wall needs a solid, compacted base, but only some need a poured concrete footing. Segmental block walls sit on a compacted gravel pad with the first course partly buried. Poured concrete walls sit on a reinforced footing sized by an engineer, and in Duluth that footing's depth counts toward the city's 4-foot permit line.
Segmental block walls (Allan Block, Versa-Lok and similar) sit on a compacted aggregate base. Allan Block's residential installation manual calls for a trench 24 inches wide (18 inches for walls under 4 feet), dug 6 inches deep plus 1 inch for every foot of wall height, with at least 6 inches of wall rock compacted in two passes of a plate compactor. Versa-Lok's installation tips describe a leveling pad about 6 inches thick and 24 inches wide, with the first course buried about a tenth of the exposed wall height. That buried course helps anchor the bottom of the wall.
Poured concrete walls are different. A cantilever wall is a reinforced concrete stem cast onto a concrete base footing, and the footing's size is part of the engineering (WisDOT Bridge Manual, ch. 14). Building foundations around Duluth go down 5 feet for frost (Minn. R. 1303.1600), and at least 48 inches in Wisconsin; a rigid concrete wall can't flex when the ground heaves, so how deep its footing goes is the engineer's call, not a guess.
Duluth measures a wall from the bottom of the footing to the top, and a wall over 4 feet, or any wall holding up a driveway or building, needs a building permit and plans stamped by a Minnesota-licensed structural engineer (City of Duluth).
Weep holes, drainage stone and drain pipe
Water is the load that brings walls down. WisDOT's retaining wall chapter puts it directly: wall drainage is needed to prevent hydrostatic pressure and frost pressure, and poor drainage can lead to deterioration, instability and collapse. On a Duluth hillside, spring snowmelt saturates the ground behind every wall at once.
Weep holes belong to solid walls. For poured concrete cantilever walls, WisDOT drains the granular backfill with weep holes and permeable material or another positive drainage system, and uses a wrapped pipe underdrain instead where a wall borders a sidewalk or road. It also notes that weep holes can discharge water in freezing weather and build ice on the sidewalk, which is worth remembering beside a Northland front walk.
Block walls don't get drilled weep holes. Their drainage is the stone zone and the pipe: Allan Block fills the block cores and 12 inches behind the block with wall rock, and requires a drain pipe for every reinforced wall, every gravity wall over 4 feet and any site with poor drainage, vented to daylight at least every 50 feet. Versa-Lok likewise places 12 inches of drainage aggregate behind the units.
Gabion walls are the exception: WisDOT notes that rock-filled baskets drain well and don't need a pipe.
Does a retaining wall need rebar or geogrid?
It depends on the wall. Segmental block walls use geogrid, not rebar, once they pass about 4 feet or carry a load above them. Poured concrete and concrete masonry (CMU) walls use rebar, with steel bars running through the stem and footing so the concrete can resist bending. A short block garden wall in good soil needs neither.
Allan Block describes geogrid as flexible synthetic mesh made for slope stabilization and earth retention: it's laid on the compacted backfill, hooked behind the block's lip, pulled tight and buried, turning a block of soil behind the wall into part of the wall (Allan Block). Versa-Lok puts the maximum stable unreinforced height at 4 feet in the best conditions, and says walls that carry heavy loads or exceed 4 feet need soil reinforcement and often an engineered design. Clay, slopes above the wall and a driveway nearby all push that height down. Bars pounded through dry-stacked landscape block are no substitute for geogrid on a tall wall.
Retaining wall types and their parts
| Wall type | How it holds | Typical use | Good to know |
|---|---|---|---|
| Segmental block (gravity) | Its own weight, plus a slight setback into the slope | Garden walls and low grade changes | Unreinforced only to about 4 ft in the best conditions, per Versa-Lok |
| Segmental block with geogrid | Block tied into layers of geogrid laid back into compacted soil | Taller walls, walls with slopes or loads above | Engineered design past Duluth's 4-ft line |
| Poured concrete cantilever | A reinforced concrete stem on a footing whose heel sits under the retained soil | Driveway cuts, walls next to buildings | Needs rebar, an engineer and weep holes or a drain |
| Counterfort | A cantilever wall with concrete webs on the back tying stem to footing | Very tall highway and commercial walls | Rarely a home wall; WisDOT adds them over 28 ft |
| Gabion | Wire baskets filled with rock, stacked and tied together | Slopes where equipment access is limited | Well-draining and flexible; the wire needs corrosion protection |
| Timber or sleeper | Stacked timbers, or boards between posts, often with tiebacks | Older low walls and garden beds | Wood in wet ground rots from the base and the buried tiebacks |
| Boulder (rockery) | Large stones stacked in a trapezoid shape | Natural-looking walls on big lots | Needs equipment; WisDOT limits them to about 8 ft |
The parts of a wall. On a cantilever wall, the stem is the upright wall itself and the footing is the slab beneath it. The footing's front edge, on the downhill side, is the toe; the part reaching back under the retained soil is the heel, and the soil's weight on the heel helps hold the wall down. The top course of a block wall is the cap, sometimes called coping. A block wall's slight lean back into the hill is its setback.
Two things people ask about don't apply to ordinary home walls. Cantilever walls don't need columns; the stiffening webs on very tall ones are counterforts, set on the back. And a retaining wall isn't a shear wall: a shear wall braces a building against sideways loads, while a retaining wall holds back soil.
For costs, national guides put a new retaining wall at about $3,192–$9,208, according to HomeAdvisor, or $15–$45 per sq ft of wall face according to Fixr. Those are U.S. ranges, not our prices. See retaining walls for new walls and retaining wall repair for failing ones; why retaining walls fail covers the warning signs. On a steep lot, terracing with shorter walls can keep each one under the engineering line.
Does a retaining wall need weep holes?
A poured concrete or mortared wall should have weep holes or an equivalent drain. WisDOT drains the backfill behind its cantilever walls with weep holes and permeable material, or a pipe underdrain where a wall borders a walk.
Segmental block walls don't get weep holes: they drain through 12 inches of clean stone behind the block and, on taller or reinforced walls, a perforated pipe vented to daylight.
Where is the toe of a retaining wall?
At the front of the footing, on the downhill side. On a poured concrete cantilever wall, the footing extends past the face of the stem toward the low side, and that projection is the toe; the part running back under the soil is the heel. People also say "toe" for the ground at the base of the wall's face.
How deep should a retaining wall's base be?
For a segmental block wall, Allan Block's residential manual digs the trench 6 inches deep plus 1 inch for every foot of wall height, and lays at least 6 inches of wall rock compacted in two passes. That puts the first course partly below grade, which helps anchor the bottom of the wall.
A poured concrete wall is different: its footing depth is part of the engineering, and around Duluth frost reaches 5 feet down.
Is a retaining wall considered a structure?
For permits, yes once it's tall or loaded. Duluth requires a building permit and engineer-stamped plans for a retaining wall over 4 feet, measured from the bottom of the footing, or any wall holding up a driveway or building. In Duluth, shorter walls carrying no such load need no building permit.
Superior's no-permit list doesn't include retaining walls, so call building inspection at (715) 395-7288 before you build there.
Send photos of the slope, the height you need to hold and what sits above it. Request a quote or call or text (715) 919-7956. Every wall gets a flat written quote you approve before work starts, with the base, stone and drain spelled out.
Next steps. For this kind of work, see our retaining walls page and How Much Does a Retaining Wall Cost in Duluth, MN? We serve Duluth and Superior.
Keep reading: Fence or Retaining Wall Between Neighbors in MN and WI and How to Hang Shelves and TVs on Plaster Walls in Duluth.