Boulder Retaining Wall — Fieldstone Boulders Set by Machine
A slope that needs holding and a look that fits a wooded or lakeshore lot — boulders set tight, leaned back, on a base and drainage that get them through the freeze-thaw.
JMB Builders builds boulder retaining walls across the Twin Cities metro and north to St. Cloud: Minnesota fieldstone or quarried granite boulders set one at a time with a skid loader or mini excavator, leaned back into the slope, on a compacted base with clean drainage stone behind them so frost does not push them out. Priced per project after a site measure. Walls above the height where the city requires an engineer get one, and a permit.
- Priced per project after a site measure
- Boulders set by machine, leaned into the slope
- Compacted base, drainage stone and pipe behind
- Tall or loaded walls: engineer and permit
- Licensed MN contractor BC809005
When a Minnesota homeowner says rock wall, this is usually what they mean: rounded fieldstone boulders or blocky granite stacked into a wall that holds a slope. A boulder wall is heavier than a block wall of the same size and it does not need a manufactured setback lip or glue. It holds because each boulder is big, sits on the ones below it at three points, and the whole face leans back into the hill. That lean is called batter, and a boulder wall without it is a pile of rocks waiting for spring.
The build goes like this. We dig a trench along the wall line and compact class 5 in it. The largest boulders go in the bottom course, partly buried, with their flattest face out and their weight leaning back. Each course above steps back a little and every boulder bridges the joint between the two below it. Small stone is chinked into the gaps from behind so soil cannot wash through the face. Behind the wall goes clean drainage stone with a perforated pipe at the bottom that runs to daylight, filter fabric between the stone and the native soil, and backfill compacted in lifts. The top is graded so surface water goes over the wall or away from it.
Boulders need a machine. A skid loader with a grapple or a mini excavator sets each stone; the crew rolls and pries it into its seat. That means a path to the wall wide enough for the machine and a place to dump a truckload of boulders and a pile of drainage stone. Where a machine cannot reach, we build in block or smaller stone instead and say so at the site measure. Walls above the height where your city requires an engineer, and any wall holding up a driveway, a slope with a building on it or a patio, get a structural engineer's design and a permit before we dig.
What you supply
- The stone: fieldstone, granite or limestone boulders, chosen at a supply yard or from photos; we order and have them delivered
- Where the wall goes, roughly how high, and what is above it: lawn, a bed, a patio, a driveway
- A path for a skid loader or mini excavator to the wall, and a spot to dump boulders and drainage stone
- What you want at the top: a bed, lawn to the edge, a fence, or steps through the wall
What JMB supplies
- Site measure, grade check and the utility locate before any digging
- Excavation of the base trench and the cut behind the wall; spoils hauled or used to regrade
- Compacted class 5 base under the bottom course
- Boulders sourced by size and color, delivered, and set by machine with the batter the wall needs
- Chinking stone in the face joints so soil stays behind the wall
- Clean drainage stone, perforated drain pipe to daylight, and filter fabric behind the wall
- Backfill compacted in lifts and the top graded to drain over or away from the wall
- An engineer's design and the city permit when the wall's height or what it holds calls for it
- Photos of the finished wall in your job folder
How it is priced: per project
Quoted in writing from your photos within one business day. What moves the number:
- Length and height of the wall face; taller walls need bigger boulders, more base and more stone behind
- Boulder type: local fieldstone is usually the least to buy and haul, quarried granite or limestone more
- Boulder size: a wall of a few very large stones sets fast but the stones cost more each and need a bigger machine
- What is above the wall: lawn is simple, a driveway, patio or structure means an engineer's design
- Soil and water: clay that holds water needs more drainage stone and a longer pipe run to daylight
- Machine access: a clear path for the skid loader vs. a tight side yard or a fence to remove and reset
- Curves, corners and steps built into the wall
- Removing a failed block, timber or rock wall before the new one goes in
Send a photo along the length of the slope and one from below it, and tell us what sits above the wall and how a machine gets to it. We schedule the site measure from that.
How long it takes
Our estimate: a low bed or shoreline wall takes two to three days once the boulders are on site; a yard-height wall along a slope about a week. Engineered walls add the design and permit time before we start.
How your project works
- 1
Send photos, get a written quote
Send three photos of the space and a sentence about what you want. You get a clear, itemized quote within one business day. We only come out to measure first when the job needs a tape measure — no pressure, no games.
- 2
Pick materials, or bring your own
We help you choose profiles and materials that fit the house and the budget, or match your existing millwork exactly — or you buy the door or trim yourself and we install it. Everything is confirmed before the crew is scheduled.
- 3
Clean, precise installation
The crew shows up on time, protects floors and furniture, and installs with tight joints and consistent reveals. Photos of the finished work go in your job folder.
- 4
Walkthrough and invoice
We walk the finished work with you. If anything is not right, we fix it before we call the job done. Then one invoice, paid by check or direct deposit — no card fees, no payment links.
Situations and options
Fieldstone boulder wall
Rounded glacial fieldstone, the rock that comes out of Minnesota fields and gravel pits. Mixed color, natural look, the most common boulder wall on lake and wooded lots. Rounded stones need careful seating and more chinking than cut rock.
Quarried granite or limestone boulders
Blocky, flat-faced stone from a quarry. Sits tighter, stacks with fewer gaps and holds a straighter face. Costs more per ton than fieldstone but goes up faster and looks more like a built wall than a pile.
Boulder wall with steps
Flat-topped boulders or cut stone slabs set as treads through a break in the wall, each on its own compacted base. The way up a terraced slope or down to a shoreline or fire pit.
Boulder wall replacing a failed wall
A leaning block wall or rotted timber wall comes out, the slope is cut back, and boulders go in on a new base with drainage the old wall never had. Sound block from the old wall can be reused elsewhere on the site.
Tall or loaded boulder wall
Walls above your city's engineering threshold, or holding a driveway, patio or building, get a structural engineer's design and a permit. Boulder walls above that height sometimes make more sense as two tiers; we lay out both options.
Boulder Retaining Wall — Fieldstone Boulders Set by Machine: questions, answered
How is a boulder retaining wall built so it does not fall over?
Three things hold it: mass, batter and drainage. The biggest boulders go in the bottom course on a compacted class 5 base, partly buried, and every course above steps back so the whole face leans into the slope. Each boulder bridges the joint between the two below it, and small stone is chinked into the gaps. Behind the wall, clean drainage stone and a perforated pipe carry water away so the soil never freezes solid against the back of the wall and pushes it out.
Boulder wall or block retaining wall, which is better in Minnesota?
Both work when they are built on a base with drainage. Boulders tolerate a little ground movement better because there is no glue and no lip to break, they follow curves and slopes naturally, and they suit lake lots and wooded yards. Segmental block holds a straighter, tighter face, takes up less depth for the same height, is easier to build steps and corners into, and is the usual choice near a house or a patio. Boulders need machine access; block can be carried in by hand.
How big do the boulders need to be for a retaining wall?
Big enough that the bottom course is wider than it is tall and the wall gets its strength from weight, not from stacking. The bottom course carries the largest stones and they get smaller going up. We size the boulders to the wall height and what is above it at the site measure, and we order by the ton from the supply yard so the mix arrives in the sizes the wall needs. Small boulders stacked high are a garden border, not a retaining wall.
Does a boulder wall need drainage behind it?
Yes. A boulder wall drains some water through its face, but the soil behind it still holds water and freezes. Clean drainage stone against the back of the wall, a perforated pipe at the bottom running to daylight, and filter fabric between the stone and the native soil keep the backfill from turning into a block of ice that shoves the boulders forward each spring. Chinking stone in the face joints keeps soil from washing out through the wall.
Does a boulder retaining wall need an engineer or a permit in Minnesota?
Low garden and yard walls usually do not. Walls above the height where your city requires an engineer, walls holding up a driveway, patio or building, and walls close to a property line or a shoreline often do, and shoreland lots have their own rules. We check with your city at the site measure. When a design and permit are required we bring the engineer in and pull the permit as part of the job.
Can you build a boulder wall without room for a machine?
Not a real one. Boulders sized for a retaining wall are set with a skid loader or a mini excavator, and the crew needs a path to the wall and a place to dump the stone. If a fence panel or a gate is in the way we take it down and put it back. If nothing wider than a wheelbarrow can get there, we build the wall in segmental block or smaller stacked stone instead and tell you that before we quote.
Can you build boulder steps into a hillside?
Yes. Boulder steps are large flat-topped stones set into the slope one above the other, each on a compacted base and dug in so it cannot slide. The slope is cut to fit, the side of each step is held with smaller boulders or the wall itself, and every tread is set level with an even rise so the steps walk right. They can run beside a boulder wall or through the middle of it.
Recent JMB work, from our job log
59 installs recorded across 30 Twin Cities communities since Dec 2025. Window and door installs for homeowners and for the builders and dealers we sub for. Counts come straight from our job log; no customer names.
Get a written quote for this job
Three photos and a sentence is enough. You hear back within one business day. Or text the photos to 763-204-2099.
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Read morePage reviewed September 27, 2026 · JMB Builders LLC, MN license BC809005 · All pavers pages
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