How much does an Allan Block concrete retaining wall cost?

Offering reliable landscaping services to homeowners in British Columbia since 2013

One of the first three questions we all think when looking at buying something is how much does it cost. Retaining walls are designed to restrain soil  to a slope that it would not naturally keep to (typically a steep, almost vertical, or vertical slope). Areas that retaining walls are used in areas where the outdoor space and  landscape needs to be shaped severely, and engineered for a more specific purpose, like hillside farming, or roadway overpasses. A professional engineer should always be brought in when necessary to ensure the integrity of wall. 

There are many factors that affect the cost of a concrete retaining wall. These include but are not limited to, how high the wall is, whether a permit is needed, access to the site, ect. 

 

A typical retaining wall will cost between $10,000 and $50,000

I’m going to give you two scenarios to help paint the picture behind the pricing I just gave you. In all likelihood your project will either match one of the two examples or fall between.

Now the reason I gave such a wide range, is it really does depend.

Our first example will be for a Structural Retaining Wall 25’L x 3’H high built to Allan Block specifications found HERE in the commercial installation manual.

For a 25’ x 3’ Allan Block retaining wall expect to pay between $12,000 - $15,000

For this price you can expect your driveway, flower beds, walkways  and lawn protected or remediated afterwards from heavy equipment, a structural retaining wall built to last a lifetime, and of course a fully insured, licensed and reliable construction company handling your project.

What is typically included when building a retaining wall?

  • Creating an excavation ticket with BC1CALL
  • Protecting concrete areas and lawns
  • Excavation of the site
  • Hauling/disposal dump truck & trailer of soil
  • Hauling and importing gravel to build site
  • Building the gravel wall foundation
  • Construction of the retaining  wall
  • Proper Drainage system tied into existing source
  • Backfilling and compaction behind wall
  • Site clean-up, lawn repair if damaged

What could drive the price of a retaining wall higher?

  • Limited space that doesn’t allow heavy equipment or material stockpiling
  • Any demolition of an old wall ( wood retaining wall or concrete retaining wall), fencing, or landscape
  • Structural support design for fencing installed near any part of the wall
  • Working around detailed landscaping that needs to be fixed afterwards
  • Protecting surfaces in excess of 100’ (laying down plywood to drive on)
  • If preventing damage is not practical then thorough remediation after project is complete
  • Buried and unexpected finds underground (although rare its worthy of a mention)
  • Soil conditions: Geogrid may be required for walls higher than 13” in clay soils
  • Length or complication of tying proper drainage system into appropriate source (storm drain, sump basin etc.)

What could drive the cost of a retaining wall down?

  • Wide open site allowing bigger or more efficient equipment
  • No existing retaining wall requiring demolition
  • No fencing in or around retaining wall
  • No detailed landscape in front or behind wall ( flower beds, walkways) 
  • Not needing surface protection
  • Wall being built prior to finished outdoor space landscape, and not have to tidy up from wall construction
  • No excavation surprises
  • Soil conditions: Water permeable soil that reduces the need for Geogrid, or as much gravel as normal
  • A nearby proper drainage system that can accept the water from behind the wall

For a 75’ x 6’ high Allan Block retaining wall expect to pay between $45,000 - $49,000 including permits and engineering

Allan block retaining wall with flower beds

While this retaining wall is subject to much of the same factors as the smaller wall, we need to point out some pretty substantial differences.

Somewhat confusing is the maximum height of the wall before  needing a permit, professional engineering, or Geogrid. It is most common to think that over 4’ you must meet these 3 requirements. The truth is, this is not entirely accurate.

A gravity wall is defined as a wall without reinforcement such as Geogrid or No Fines Concrete. A wall as low as 13” could require reinforcement, while in another scenario a maximum wall height of 9’ 8” could be built without any reinforcement.

Separately most cities require a permit and structural engineering on any wall over 3.9’.

The requirement for reinforcement or permits and professional engineering is independent of each other. Its variables like these that make taller walls a little more complex.

The exact cost of these engineered wall systems will vary, as engineers take into account the exact site conditions which will include slopes above or below the wall (a land slope analysis may be required), soil structure, location of wall on property, and other factors.

For the permit, and typical Engineering expect to pay between $3600-$5000

The last substantial difference in a small retaining wall vs a larger one is the drainage system.

A wall that requires reinforcement such as Geogrid automatically requires a 2nd system called the heel drain. This drain captures water further away from the wall, and lowers the surcharge on the wall.

There are a lot of variables when designing and building a concrete retaining wall. In every case their job is to hold back a lot of weight for a lifetime. 

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