What do retaining walls cost?
The cost of a retaining wall is very dependent on the materials used to retain the soil, as well as the site address, and the site access.
Wooden retaining walls are slightly cheaper than Allan Block, but not so much cheaper that it’s usually worth doing, when compared to how much longer Allan Block will last.
For an Allan Block retaining wall a small wall 25’ x 3’ is around $10,000,
an Average size wall 70’ long and 3.5’ high is just under $25,000,
and a large 2-tiered wall 85’ long 3.5’ high is about $50,000.
Now while those prices are usually pretty accurate there are some factors that could make the cost go down, there also some factors that could significantly make the price go higher.
Let’s talk about the biggest factors that influence the price.
Excavation and soil disposal.
Most older retaining walls are in a state of failure. On the minor side of failure, you have uneven gaps, or spaces between the blocks, or they are unlevel, and no longer straight and true.
In the most extreme cases you have bowed walls, walls that were once angled back are now straight up and down, or even quite frequently, you have walls that have shifted and have separated creating gaps over an inch wide.
This is all a result of not excavating enough soil beneath and behind the wall.
A common way to lower the cost of a retaining wall project is to limit the amount of soil excavated, hauled, and disposed of. This will 100% cause problems down the road.
The 2nd biggest influencer in project price is the amount of gravel used under and behind the wall.
Gravel should be 6” thick PLUS 1 additional inch for every 1 foot of wall height. This means a 4’ high wall should have 10” minimum of gravel underneath it. Behind the wall you need a minimum of 16” to a common maximum of 24”.
This is all to commonly cheated due to the cost, and lack of knowledge with how important this is.
Excavating and disposal of the soil, and using enough gravel to provide a suitable foundation are the biggest factors that affect the price, but a few other factors that can affect your project are:
Using plywood for temporary roads to protect surfaces or lawns.
Replacing nearby landscaping after construction.
Site width access for excavator, skid steer, or tracked dumpers.
Site working area for stockpiling materials, and tools.
There are lots of factors that have gone into providing a ballpark price for how much a retaining wall costs. Remember that each space is different, and these costs are a baseline for how much a retaining wall project costs.