On a sloped Duluth yard, two or three short walls often beat one tall one. Each holds back less soil, a wall up to 4 feet carrying no driveway or building needs no Duluth building permit, and every tier gives a level bench. The catch is spacing: tiers too close together load each other and act like one tall wall.
One tall wall or several short ones
Both approaches hold back the same hill. The difference is how the load is split up and what you get to use afterward. A single tall wall gives you one big flat area on top with the least horizontal room, which is useful when the space is tight, such as a driveway cut or a narrow side yard. It also concentrates all the soil pressure on one face, which is why tall walls need reinforcement and, past a certain height, an engineer.
Terraces split the grade into steps. Each wall is short enough to build as a simpler gravity or lightly reinforced wall, and each bench between walls becomes a garden bed, a path or a spot for chairs. The cost is space: you need more depth front to back to fit the tiers and the gap between them.
| Factor | One tall wall | Several short walls |
|---|---|---|
| Permit in Duluth | Needed once it's over 4 ft from the bottom of the footing, with engineer-stamped plans | None for a single wall up to 4 ft holding up no driveway or building; the city publishes no rule for tiers, so ask about close spacing |
| Engineering | Required over 4 ft; geogrid reinforcement likely | Under Allan Block's rule, not needed when tiers sit at least twice the lower wall's height apart; needed if closer |
| Usable ground | One level area at the top | A flat bench at every tier, for beds, paths or seating |
| Space needed | Least horizontal room | More room front to back, because of the spacing rule |
| Drainage | One drainage system, but water pressure on one face | A gravel zone behind every wall, and outlets planned so upper tiers don't drain onto lower ones |
| If it fails | The whole slope can come down at once | Usually one tier, though a failed lower wall can undermine the one above |
| Look | A single tall face | Softer, stepped look that plantings can cover |
Permits are often the deciding factor. In Duluth, a retaining wall needs a building permit and plans stamped by a Minnesota-licensed structural engineer when it's over 4 feet tall, measured from the bottom of the footing to the top of the wall, or at any height when it holds up a driveway or building (City of Duluth). The city's page says nothing about tiered walls, so don't assume close tiers count as separate short walls: ask Construction Services how it will treat your layout before you settle it. In Superior, retaining walls aren't on the no-permit list, so call building inspection at (715) 395-7288. The Duluth and Superior permit guide has the other outdoor rules.
How far apart the tiers need to be
An upper wall set close behind a lower one sits on the soil the lower wall is holding back, so its weight, plus the soil it retains, becomes extra load on the lower wall. Allan Block's terracing guide sets the rule for its block: the distance between walls must be at least twice the height of the lower wall, and the upper wall should be no taller than the lower one. Closer than that, Allan Block says the layout needs engineering, because the lower wall carries the added load. The same guide lists slopes above or below the walls, groundwater, surcharges and bad soils as conditions that call for engineering too.
In practice, a 3-foot lower wall needs at least 6 feet to the next wall. On a steep, short lot that math sometimes doesn't fit, and then the honest answer is fewer tiers, a gentler finished slope, or one engineered wall. Other block makers publish their own spacing rules, so the rule for your wall comes from the system you build with.
Drainage for each tier
Every tier is its own wall and needs its own drainage. Allan Block's installation manual calls for 12 inches of clean gravel behind the block on each course, and a perforated drain pipe for reinforced walls, walls over 4 feet and sites with poor drainage, set at the back of the base trench and vented to daylight at least every 50 feet. On a Duluth hillside, snowmelt soaks every tier at once, so plan for pipes.
The part that gets missed is where each pipe comes out. An upper tier that empties onto the bench below just sends its water into the next wall's backfill. Run outlets to the side of the terraces or down to a spot where water can leave the yard, and grade each bench to shed water forward, away from the wall above it. Keep downspouts off the terraces entirely. The retaining walls page covers how we build the base and backfill.
Materials and planting the terraces
Materials. Segmental concrete block is the usual choice for terraces because every tier can match, the units set their own backward lean, and caps give a finished edge. Boulders suit wooded lots and look natural in steps, but setting them takes equipment and room to work. Timber is the lowest upfront cost and the shortest-lived, since wood in wet ground rots from the base. For budgeting, national cost guides put a typical new 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; for terraces, count the face area of every tier.
Planting. Allan Block's manual tops the backfill behind the last course with organic soil so plants can grow, and its terracing guide notes that planters often get irrigation and says the plan needs provisions for water management. Water the beds with soaker hoses or drip rather than flooding them, since a soaked bench pushes on the wall below. Perennials, groundcovers and low shrubs hold soil without heaving the wall; keep trees and large shrubs back from the walls, where their roots can push on the block. Mulch the benches so rain soaks in slowly instead of washing soil over the caps.
How far apart should terraced retaining walls be?
At least twice the height of the lower wall, under Allan Block's rule for its block, so a 3-foot lower wall needs at least 6 feet to the next tier. Closer than that, Allan Block says the upper wall adds load to the lower one and the layout needs engineering. Other block systems publish their own rules, so follow the one for the block you're using.
Is it cheaper to build two short walls than one tall one?
Often, but not always. Two short walls can avoid the permit and engineered design a Duluth wall over 4 feet needs, though the city publishes no rule for closely spaced tiers, so confirm that with Construction Services. Short walls are simpler to build. But terraces can add up to more total wall face and excavation, and they need more room. Where the slope is short and steep, one engineered wall can come out closer in price than you'd expect.
Can the upper terrace wall be taller than the lower one?
Not as a rule. Allan Block's terracing guide says the upper wall should be no taller than the lower wall, because a taller upper wall adds more load to the tier beneath it. Keep the lowest wall the tallest, or make the tiers equal. If the grade forces a taller wall higher up the slope, that layout needs an engineered design.
What should I plant on retaining wall terraces?
Perennials, ornamental grasses, groundcovers and low shrubs work best, because their roots bind soil without pushing on the block. Keep trees and large shrubs well back from the walls. Water with drip or soaker hoses so the benches never get saturated, and mulch to slow runoff. Pick plants hardy for your yard's zone and light, and group thirsty ones on the lowest bench.
Send photos of the slope from the bottom and the side, and a rough measurement of the rise. Request a quote or call or text (715) 919-7956. We'll lay out the tiers, confirm the permit picture, and send a flat written quote; our on-site service fee is waived when you approve the work.