Retaining wall installation: what to know

What the job involves, what changes the price, and what to ask a pro.

What retaining wall installation is

A retaining wall holds back soil on a slope or a grade change, and it is built from block, stone or timber over a compacted base with drainage behind it. People call for one when a yard is eroding, a slope is slumping toward the house, or a flat area needs to be terraced for use.

Signs you need it

  • Soil is sliding, washing out or slumping down a slope toward a walk, a driveway or the house
  • A flat area is needed in a sloped yard, and a wall would let you terrace it for a patio, garden or lawn
  • Water runs off a hillside and pools against the foundation, and a wall plus drainage would redirect it
  • An existing wall is leaning, bulging or cracked, and the soil behind it is pushing outward
  • Roots or erosion have undermined a slope near a pool, a patio or a garage, and the ground needs holding
  • A raised garden bed or planter needs a stable, engineered edge that will hold back the weight of the soil

What the pro does

  • Check the site for slope, soil type, water flow and any buried lines before any digging starts
  • Excavate the trench for the footing and the base, then set and compact a crushed stone base in layers
  • Lay the first course level and check it along its full length, since every course above depends on it
  • Stack block, stone or timber courses with the setback each design calls for, and add a geogrid or anchors if the design uses them
  • Place drainage stone, perforated pipe and filter fabric behind the wall so water does not build up pressure
  • Backfill and compact the soil in lifts, then finish the top course, cap and grading above the wall

What changes the price

Every job is different, so we do not publish prices. These are the things that move the quote up or down.

  • Height and length of the wall, since taller walls need more base, more reinforcement and more engineering
  • Material type, such as segmental block, natural stone or timber, each with different installation work
  • Whether the wall needs geogrid, anchors or deadmen to resist soil pressure behind it
  • Excavation depth and access to the slope, including whether machines can reach the wall line
  • Drainage elements such as perforated pipe, drainage stone and an outlet to daylight or a drain
  • Whether a stamped engineering design, a permit or an inspection is required for the wall

What a written quote should spell out

  • Wall height, length and the setback named, with the material type and block or stone size
  • Base depth, stone type and compaction method for the footing and the base
  • Reinforcement used, such as geogrid, anchors or deadmen, and their spacing as the design calls for
  • Drainage details, including the stone, pipe and filter fabric, and where the water exits
  • Engineering or design documents, and whether the permit and inspection are included
  • Backfill, grading and any landscaping above the wall, listed as separate lines

Questions to ask before you hire

  • Does this wall need an engineered design, and who will stamp it?
  • How deep is the footing, and how do you compact the base under it?
  • What drainage will you put behind the wall, and where will the water go?
  • Will you use geogrid or anchors, and how far into the slope do they extend?
  • What do you do with the soil behind the wall during backfill?
  • Who pulls the permit and schedules the inspection for this wall?
  • What happens to the wall if the soil moves or the drainage fails later?

Red flags

  • Builds a tall wall without an engineered design or a plan for the soil pressure behind it
  • Skips the drainage stone and pipe behind the wall
  • Sets the footing on loose fill or topsoil without digging to firm ground
  • Says geogrid is never needed on a wall that is holding a real slope
  • Does not check for buried utilities before excavating the trench

What you can do yourself

A homeowner can build a short, low, decorative border wall of stacked block on a level base, with a clear drainage plan. Call a pro for any wall that holds back a real slope, is tall, is near a house or a road, or is reinforced with geogrid or anchors, since failure can be sudden and dangerous. Block is heavy and trenches can collapse, so keep out of excavations deeper than your knees and wear gloves and steel-toed boots.

Licenses and permits

Retaining walls are commonly done by licensed contractors, and taller walls often require an engineered design and a permit in many areas. Check with your state or local licensing agency and your local building department before work starts, and ask who will provide the design.

Retaining wall installation questions

Why does my retaining wall lean or bulge?

Leaning and bulging usually come from water pressure building up behind the wall, from a weak base or from a wall that was taller than its design allowed. A pro should check the drainage, the base and the soil before a repair is planned.

Do I always need an engineer for a retaining wall?

Not every wall does, but taller walls, walls that hold a slope close to a house or road, and walls with surcharge loads usually need an engineer. Ask the pro how the design was determined and who signs it.

How long does a retaining wall last?

Its life depends on the materials, the base, the drainage and the soil, so a well-drained wall on a firm base can last many years. Ask the pro what maintenance they recommend for the drainage and the top course.

About this guide

This national guide is written and checked by infinibell. Rules and conditions differ by place, so local pros are credited on guides for the cities they serve, not on national ones.

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