Retaining walls
Retaining walls fail for one reason: water. Not soil weight — water. Saturated soil weighs roughly twice what dry soil does, and in Minnesota it also freezes and expands behind the wall. Every wall we build is a drainage project first.
How we build them
- Excavate and level a base trench below frost-affected fill
- 6 to 12 inches of compacted aggregate base, level and hard
- Bury the first course — one-tenth of wall height, minimum one full block
- Drainage aggregate at least 12 inches behind the full wall face
- Perforated drain tile at the base, daylighted or tied to a drainage point
- Geotextile fabric between the drainage stone and the backfill soil so it never clogs
- Compact backfill in lifts as the wall goes up
- Geogrid tied into the soil mass on anything over 4 feet
- Cap course adhered, and grade above the wall pitched to shed water away
The buried first course and the drain tile are the two things cheap walls skip, and they are exactly why those walls are leaning within five years.
Materials
| Type | Installed per face sq ft | Best for |
|---|---|---|
| Segmental concrete block | $35 – $60 | Most walls; huge style range |
| Natural stone / limestone outcropping | $55 – $95 | Highest-end look |
| Boulder wall | $40 – $70 | Large grade changes, rural look |
| Poured concrete with veneer | $60 – $110 | Tight spaces, engineered situations |
| Timber | $25 – $45 | Cheapest; expect 15 to 20 years |
Typical project cost
| Wall | Range |
|---|---|
| 20 ft x 3 ft garden wall | $3,000 – $6,500 |
| 40 ft x 4 ft wall | $8,000 – $16,000 |
| Terraced walls with steps | $15,000 – $35,000 |
| Wall with integrated seating and lighting | $12,000 – $30,000 |
Estimates for planning.
The 4-foot rule
In nearly every Twin Cities city, a retaining wall over 4 feet in exposed height requires a permit and an engineer's design. Terracing two 3-foot walls does not automatically get you out of it — if they are close together, the code treats them as one structure. We tell you up front which category you are in rather than finding out at inspection.
What's included
- Free, no-pressure estimate
- Licensed & fully insured crew
- Cleanup included — we leave it spotless
- Same-day or scheduled service
- Written quote, fair pricing
- 24/7 emergency response
FAQ
Do I need a permit for a retaining wall?
Generally yes above four feet of exposed height, and that usually requires engineered plans as well. Under four feet, most cities do not require one, but check for easements and setbacks.
Why do retaining walls lean or fail?
Almost always water. No drain tile, no drainage aggregate, or no fabric to keep the stone from silting up. Saturated soil doubles in weight and then freezes and pushes.
How long should a retaining wall last?
A properly drained segmental block or stone wall should last 50 years or more. Timber walls are typically 15 to 20 years before rot takes them.
Can I build on top of a retaining wall?
Not without engineering. Any surcharge load — a driveway, a patio, a structure, even a parked vehicle above the wall — changes the design requirements substantially.
Retaining Walls near you
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