Construction Systems
What is the cost of earthworks and retaining on a plot of land?
*Update: Please contact our team for current pricing.
Along with foundation costs, knowing how much earthwork and soil retention cost on a plot is one of the key questions from our clients with sloped land.
Earth retaining is a project item that can not only vary the final construction price of our home but also condition the type of structure, the settlement, and the arrangement of our home in relation to the terrain.
To determine the cost of earthworks and retaining on a plot of land, each case must be assessed individually. Nevertheless, in this post, we provide some generic indicative values.
Before delving into the mere construction costs, it is important to understand what these initial tasks on site entail, such as earthworks and retaining, as well as the factors that will influence the final price.
Let’s start at the beginning: what exactly is a retaining wall?
What is a retaining wall and how does it work?
A retaining wall is defined as an element that supports the horizontal thrust of the soil it holds.
Retaining walls are used when we cannot allow the terrain to maintain its natural slopes because we need flat surfaces to support our new home.
Structurally speaking, a retaining wall can work in two ways: by gravity or as a cantilever.
Gravity walls resist horizontal thrust thanks to their own weight; they counteract the weight of the earth with their own mass and do not require any type of foundation.
Examples include traditional stone walls, although today these are also built with gabions or solid blocks of various materials.
On the other hand, there are cantilever walls, which do require foundations. They are called this because they support their own weight without any external help. These include most concrete walls or even sheet piles driven into the ground.
While selecting the appropriate wall type will influence the final price, it will be more important to understand the type of subsoil, as earthworks and retaining on rocky terrain are not the same as on soft terrain.
Thus, to determine the cost of earthworks and retaining on a plot of land, we must carry out a geotechnical study, which will be crucial for deciding the appropriate type of retaining wall and subsequently knowing the costs.
Let’s look at the options we have according to the subsoil of our plot:
Retaining Walls by Subsoil Type
Retaining Walls for Rocky Terrain
Among the types of subsoil we may find on our plot, the hardest type is rocky terrain.
Rock is an excellent ground for foundations, as it has high resistance. In this case, it would not be necessary to build retaining walls, since once the ground is excavated, it retains itself.
However, when it comes to earthworks, it will be much more expensive and require more hours of heavy machinery than softer ground. Let’s remember that one of the most expensive items in terms of cost/result in house construction is machinery rental and labor.
Even so, it is a very suitable terrain for building, as the foundation of our house will be smaller, provided we do not want to build a basement, whose excavation would incur excessive additional costs.
Retaining Walls for Soft Terrain
There are also non-cohesive soils, which are those that lack adhesion between loose grains.
Examples include gravel, sand, or loose coarse stones. Unlike rocky terrain, soft terrain allows for relatively easy earthmoving, but retaining walls will be needed to prevent collapse.
Retaining Walls for Cohesive Soils
Cohesive soils, such as clay or mud, have a high capacity for cohesion, as their name suggests. This means they are self-supporting once earthworks have been carried out, and although they are not as stable as rock, the pressure of cohesive soils on our retaining wall will be lower.
Thus, retaining walls in cohesive soils present a risk of landslides.
It should be noted that cohesive soils tend to be less permeable, which will require us to plan for some type of drainage to prevent water accumulation, which would generate greater weight.
Retaining Walls for Poor Soils
Finally, we have poor soils. These are types of soil unsuitable for foundations.
It is true that today it is possible to build with sophisticated structures on almost any terrain, but…
In our sustainable architecture studio, we recently evaluated construction on a poor, sloping plot where the first 15 meters of depth consisted of poor fill material and non-cohesive soils until a resistant rock stratum was found. Although, at the foundation level, our structural engineer had calculated that it was possible to support the house using micropiling — large pillars inserted into the ground — and without earth retention, the cost of this operation represented such a high percentage of the total construction cost of the house that it led us to rule out building the house on this plot.
In the case of building on low-resistance terrain, it will be necessary to combine deep foundations or slab foundations — which involve founding the entire base of the house — with high-resistance construction walls designed to withstand significant earth pressures.
What is the cost of earthworks and retaining on a plot of land?
As we have already mentioned, to determine the cost of earthworks and retaining on a plot of land, many variables must be considered.
To begin, we need to define what type of earthworks we will undertake, whether we need to excavate, level, or backfill our plot, as each type of work requires different machinery that can significantly alter the final price.
We will also need to consider the volume of earth we are going to move, as this will directly affect the number of machinery hours required to extract it from the ground.
Construction machinery is usually rented by the day. Therefore, it will be important to organize the work so that the machines are not idle when on site.
A larger volume of earth to move or level will, logically, entail more hours or days of machinery operation.
The slope and access to the plot will also influence the final budget. This also refers to the machines that need to reach the site.
The hours spent reaching the access point, by both excavators and trucks, will be hours they cannot work. Furthermore, in extreme cases, it may involve requesting very specific machinery to be able to work according to the terrain.
The same companies sometimes also handle other services such as clearing the plot, felling trees, or waste management. This refers to what is done with the earth after it is removed. Depending on the company, different solutions can be found for the surplus volume.
A primary solution to avoid wasting the earth we excavate is to use it on our own plot.
Alternatively, the construction company can take charge of this earth and reuse it for another project or dispose of it at a landfill. In both these cases, a fee must be paid, either for the company to store it or to transport it to the landfill.
Following this, let’s look in detail at the cost of earthworks and retaining on a plot of land.
Example of Earthworks and Retaining Costs on a Plot of Land
Let’s look at the costs through an example of a 100 m2 house.
First, we will assess the cost of earthworks.
As an example, imagine we have a gently sloping plot where we are going to build a square-plan house.
Since our example house is 100 m2, it will have a floor plan of 10 meters wide by 10 meters long. If one side is embedded in the ground, we will need to move the earth from the slope.
Let’s assume that out of these 10 meters in length, we need to excavate 3 meters high by 3 meters wide, which amounts to a total of 90 m3 of earth. Based on our experience in real construction cases, we should start with a generic rate of approximately 12 euros/m3 of earth.
It should be noted that this is a very generic rate for average terrain that does not present excessive excavation problems, but this rate can vary depending on the type of terrain.
Thus, we have 90 cubic meters of earth at 12 euros per m3 displaced, totaling 1,080 euros, including transport and earth management.
Furthermore, it is also necessary to remember that the price of earthworks will vary greatly depending on the volume of the project and all that it entails.
We continue the construction process to assess the cost of a retaining wall.
Once earthworks have been completed, it is necessary to construct the retaining wall.
How much does a retaining wall cost?
Now let’s get to what interests us: how much do earthworks and retaining walls cost on a plot of land?
Following the previous example, imagine that after moving 90 m3 of earth, we are left with 10 meters of non-cohesive soil that we must retain with a wall before building the house.
As it is a sloping terrain, we will assume that these 10 meters in length require a retaining height, based on calculations of soil resistance, of 2 meters high.
Well, if we solve these 10 linear meters by 2 meters high with a solid block wall, the total cost would be between 1,500 and 2,000 euros.
If we opt for a gabion wall, considering a concrete base layer and the gabion itself, it would cost us around 1,400-1,800 euros.
Finally, the “low cost” option for retaining walls, if we consider a conventional concrete wall, the final amount ranges from 600 to 1,000 euros.
However, as we have mentioned, it is necessary to evaluate each case individually and decide the type of retaining wall based on the needs of the terrain and the project.
Applicable Regulations for Earthworks and Retaining
It should not be forgotten that walls, like all construction items, are also regulated by building codes.
In our studio, whenever we receive a new client who wants to build their own home and know the cost of earthworks and retaining on a plot of land, the first thing we do is review the regulations regarding earth retention, as in many cases, earthworks and wall dimensions are limited at the municipal level.
Municipalities regulate the maximum earth retention on a plot, meaning the maximum height of retaining walls. This prevents excessively tall walls from being built.
Thus, upon reaching the established height limit, we must create a new natural terrace and support it with another retaining wall. This is regulated with the aim of integrating houses into the terrain to some extent, in addition to achieving uniformity in the built environment of a territory.