Precautions to Consider When Building on a Sloped Plot

While building on a sloped plot is a topic we have previously addressed on this blog, many clients approach us with doubts about whether to purchase a sloped plot due to concerns about the potential additional costs involved in constructing a house.

For this reason, today we wanted to offer a more practical post than usual, summarizing the three recommendations to consider when building on a sloped plot. This will provide you with a basis for objectively evaluating different plots and understanding the pros and cons of your decision.

As always, first and foremost, we recommend contacting an architect before purchasing land. You can reach out to us, as our studio offers complimentary assistance in land search, or consult your trusted architect before making a decision. This is because, in addition to assessing the slope, it is crucial to evaluate the surroundings, regulations, and even legal risks associated with buying and selling a property, ideally with the guidance of an experienced professional.

1. Reduce earth movement and retention

Our clients’ key question regarding costs.

Buying a sloped plot is always cheaper than buying a flat plot, as a sloped plot must be leveled to build the house.

The question is, does the cost of leveling the plot offset the reduced cost of buying a sloped plot?

Generally, yes, in the sense that earth movement and retention are usually not as expensive as the increased value of flat plots, in our experience. However, there are nuances.

If we purchase a sloped plot, we cannot expect to flatten it entirely with retaining walls. We must adapt to the uneven terrain, either by building our house on different levels or by constructing a smaller house on a single level.

In any case, we must always remember that there will be stairs to access the house, whether we enter from an upper or lower level.

Nevertheless, adapting the construction to the slope allows us to optimize land use and reduce earth movement and retention, leading to a consequent reduction in construction costs.

Working with the natural contours of the land will be essential when building on a sloped plot. This will also foster a connection with the terrain and likely provide more access points to the exterior.

The more excavation and earth removal, the greater the variation from the original ground level. This means that we will not be able to ventilate or illuminate rooms in these situations. Even so, we can always locate occasional-use spaces such as storage rooms or garages where natural ventilation or light is not essential. Another solution is to illuminate these areas through patios that extend to the lowest level.

Finally, regarding earthworks on a sloped plot, it is necessary to consider that construction machinery is paid for based on the hours it is needed. For this reason, the fewer days required, the more we can save.

However, it is not advisable to focus solely on savings. It is preferable to consider the house’s conditions and individual needs. One must remember that a home is for life and weigh each decision, prioritizing every investment.

Earthworks

Earthworks refer to the volume of soil or subsoil that is moved from one place to another. This includes both the soil extracted from the plot and that which is incorporated.

Since people live on horizontal surfaces, earthworks for building on a sloped plot will be significant. The ideal approach is to use the extracted soil to fill other areas of the plot, ensuring that earth movement remains within the plot itself and minimizing waste.

Earthworks require specialized machinery, depending on the hardness of the subsoil, and the ability to access sloped and unstable areas. Therefore, the difficulty of vehicle access to the site for all necessary vehicles must be anticipated.

Earth Retention

When earth movements occur, we must ensure that the subsoil does not collapse or cause problems; for this, it will be necessary to construct retaining walls.

The height of retaining walls may be regulated by local municipal ordinances. Therefore, one of the recommendations to consider when building on a sloped plot is to review the municipal regulations regarding earth retaining walls before purchasing the land.

As we explained in a previous article, there are different types of retaining walls that must be evaluated in each case.

When a house is built, these will almost always be structural walls that, in addition to retaining the earth, will also serve as support for the dwelling.

While the type of wall will influence the final price, it will be more important to understand the subsoil to determine which wall to use. By working with split levels, the walls will be shorter, but there will likely be more of them.

Understanding the subsoil type is always important for a project, but it holds particular significance when building on a sloped plot.

Subsoil strata are usually arranged more or less horizontally. Therefore, it is important to know the depth of the different strata and, especially, the resistant stratum on which the dwelling will be supported.

At Slow Studio, we always accompany clients on site visits to get an idea of the existing subsoil type. If there are any doubts, we send our geologist to conduct a preliminary soil test.

A preliminary soil test involves taking a soil sample at a certain depth for analysis to quickly define the subsoil characteristics. It is very useful when only a preliminary idea of resistance is needed and a geotechnical study is not yet required. Moreover, it is a very economical procedure as it only involves a few hours of the geologist’s on-site work.

Geotechnical Study

Before starting a project, it is mandatory and essential to conduct a geotechnical study to determine the type of subsoil available and, consequently, the foundations that should be used.

A geotechnical study involves gathering information from various boreholes located at controlled points on the site. Subsoil boreholes are points where a rod is driven in, simultaneously measuring the resistance offered by the ground. This is performed at different depths to understand the various soil strata.

3. Assess the presence of water

Finally, and something not always checked when building on a sloped plot, is the presence of water or its runoff.

If we are on a sloped plot, it will be difficult for the dwelling to flood, but depending on the topography, the lower part of the plot could be covered. Although it is most likely that the dwelling will be built on the higher part of the plot, construction should anticipate flooding in each part of the land.

Furthermore, we must also assess the presence of groundwater. Subsurface currents could, in the worst-case scenario, damage the house’s foundations.

They can also weaken the ground and its characteristics.

The same geotechnical study performed to determine the subsoil composition will also identify the presence of water and the degree of soil moisture. In addition to the geological study, there is also the possibility of conducting a geobiological study, which helps detect natural influences such as underground currents.

Finally, it will also be necessary to ensure proper water runoff. When building on a sloped plot, water is less likely to stagnate. Nevertheless, it will be necessary to secure the interfaces between the ground and the house or any earthworks carried out, and to anticipate runoff from the plot itself or adjacent plots.