Cost guide

What a Retaining Wall Really Costs in Middle Tennessee

Two walls the same length on the same street can be double each other. Almost all of the difference is buried behind the face, in the base, the backfill and the drainage.

Why nobody can price a wall over the phone

Retaining walls swing wider than anything else we bid. Two walls of the same length, on the same street, can come in at double each other. The homeowner with the cheaper number is not always the one who got the better deal.

The reason is that most of a retaining wall is buried. You are paying for the base trench, the compacted backfill, the drainage stone and whatever reinforcement holds the hillside back. The face you look at is the last part built and the smallest part of the cost.

So treat the ranges below as budget setting, not as a quote. Only somebody standing on your slope with a shovel, a level and a tape can turn them into a real number.

Height decides how much engineering the wall needs

Height matters more than length. A wall holding two feet of soil is landscaping. A wall holding six feet is a structure, and the load it carries climbs faster than the height does.

Somewhere around four feet, most jurisdictions want a design stamped by a licensed engineer, and the height is usually measured from the bottom of the footing rather than from the grass you are standing on. A wall that looks three feet tall can already be over the line. Confirm the trigger and how it gets measured with the Rutherford County building department before you plan around it. That call is theirs, not ours.

Once a wall crosses into engineered territory, the cost moves in three places at once. The design fee. Geogrid, a reinforcing fabric laid back into the hill in layers, which means excavating well behind the wall face. And a deeper base with a heavier unit.

What the wall is built from

Materials sort into a few families around here. Segmental concrete block is the workhorse: a dry stacked unit with a lip or pin that sets the batter, quick to build, and what most subdivision walls in Smyrna and La Vergne are made of. The National Concrete Masonry Association publishes the design and installation guidance that whole system is built around, and a contractor working with the product should be able to talk about it.

Mortared natural stone sits at the other end. Tennessee fieldstone on a poured footing belongs on the site, but it is slow work and the labor is where the money goes.

Rough figures per square foot from Middle Tennessee wall builders, before site work and drainage:

• Segmental concrete block, the subdivision workhorse: $15 to $25 per square foot in this area
• Engineered block above four feet: over the plain block range, since a design fee, geogrid and a deeper base all land on the same wall
• Mortared natural stone: $25 to $45 per square foot, and the gap from block is nearly all labor
• Poured stem wall with a stone or brick facing: normally the highest of the three
• Engineer's design, where required: $1,000 to $3,000 as its own line item

Drainage is the part that decides whether it lasts

Nearly every failed wall we get called to look at failed the same way. Water got behind it and nothing let the water out.

Our clay makes that worse than it sounds. Middle Tennessee clay shrinks hard through an August drought and swells again when the spring rain returns. Saturated clay pushes on a wall with far more force than dry soil does, and a wall designed for one and asked to hold the other is on a countdown.

Real drainage means a zone of clean stone behind the full height, filter fabric so silt does not clog it, and a perforated pipe at the base that actually goes somewhere. It costs money and none of it shows. It is also the single line item separating a wall you forget about from one that leans in six years.

• Clean angular drainage stone behind the full height of the wall
• Filter fabric between that stone and the native clay
• A perforated pipe at the base with a real outlet, not a dead end
• Backfill compacted in lifts instead of dumped and walked on
• Grading above the wall that carries surface water away from it

Rutherford County ground: rock in places, clay in the rest

Excavation is where a quote here goes sideways. We sit on limestone, and the depth to that rock can change across one back yard.

Hitting rock in the base trench is not bad news structurally. Rock is an excellent thing to found a wall on. It is bad news for the schedule, because a bucket stops working and a hammer starts, and hammering limestone is slow and gets billed by the hour. That is worth settling before the machine arrives rather than after. A contractor who builds on this ground will tell you how rock gets billed and will write it into the quote instead of mentioning it later.

Karst country supplies the other surprises. Seams, voids and wet weather springs reveal themselves only after the ground is open, and a spring behind a wall changes the drainage design completely. A contractor who bids your slope without asking what the neighbors hit is guessing at your expense.

Access, spoil and the things that quietly add days

After height and drainage, the biggest swing is how easily a machine and a pallet of block reach the work.

A wall along an open driveway is straightforward. The same wall in a fenced back yard on a steep lot, where every unit goes down by hand or by buggy, can carry twice the labor. Older streets near the Murfreesboro square and the tight lots around MTSU rentals are where this bites hardest. Then there is what comes out of the hole. Spread on site, excavated clay is nearly free. Hauled off, it is another line on the invoice.

• Gate width, and whether a machine can reach the work at all
• Turf and slope a tracked machine will tear up and have to restore
• Hauling spoil off site versus spreading it on the lot
• Utility locates, plus irrigation and pet fence lines nobody marked
• Steps, caps, curves and corners, all cut work and all slower than straight run

Turning a range into a number

A site visit exists to answer questions a phone call cannot. How tall is the wall at its worst point, not its average. What is the soil doing after rain. Where does the water go once it leaves the pipe. Is there rock, and at what depth. Can a machine get in.

A quote worth comparing names the unit and the wall type, the exposed height and length, the base depth, the drainage detail, whether an engineer is involved, and what happens to the excavated soil. Two quotes that do not both describe those things are not comparable, however close the totals look. And until somebody has walked your slope, every figure on this page is a budget, not a bid.

Related services: Brick Masonry · Stone Masonry