How to know whether a plot of land is suitable for building?

When looking for a plot to build a house, there are many factors to consider when choosing. One of the first questions we receive when it comes to the purchase decision is how to know whether a plot of land is suitable for building.

The characteristics of the subsoil will of course be key, but it is also important to look at other aspects such as orientation or the presence of water, among others.

In today’s post we have defined the 7 most important aspects of how to know whether a plot of land is suitable for building, so that when you face the process of searching for and comparing plots you have all the information available to make a decision.

1 Orientation

The first step is to check the orientation. It may seem very basic, but it is perhaps the most important factor to consider and will be key to building a home that can benefit from natural daylight and solar heat, thereby reducing energy consumption.

South-facing orientation

Especially if it is a sloping plot, a south-facing orientation will be crucial for the home to perform properly. To naturally light and heat a home, a main south-facing façade with a substantial window area is essential.

For this reason, you should look at the plot’s proportions. In other words, if the south-facing width is narrow, the south façade will probably be small. This should not be a problem because, in that case, we can design a home with an intermediate courtyard that allows two south-facing façades—one at the front and one at the rear—but this will increase construction costs. Therefore, it is better to find plots with a considerable width on the south side.

North-facing orientation

Orienting a house to the north is thermally unfeasible, as a great deal of heat is lost. There is also hardly any solar radiation, so light is limited. On the north side, it is preferable to place service areas such as bathrooms, laundry room, pantry, garage or, failing that, rooms that are used infrequently.

East and west-facing orientation

East and west orientations are not bad, but they have their particularities. The sun rises in the east, so an east-facing room will receive the first warmth and sunlight in the morning.

A west-facing orientation is also very suitable, as it allows you to take advantage of the last rays of sun. In many cases, the west orientation is used for the living room (which can have openings to the south and west), so that in winter it receives warmth until late afternoon.

On the other hand, a west-facing orientation in summer is somewhat complex, as it requires good solar protection to shield you from the heat of long summer afternoons when the sun sets slowly.

2 Sun exposure

Continuing with sun and light, it will not only be important to check the plot’s orientation, but also its potential for sun exposure.

There is little point in having a south-facing plot if there is a building in front of it that prevents direct sunlight. In these cases, it will be necessary to consider the sun’s angle of incidence and assess to what extent the obstacle blocks sun exposure.

Obstacles can also be a mountain or vegetation such as trees, both on neighbouring land and on the plot itself. Sometimes we find ourselves in a protected area, and regulations do not allow felling even if the trees are within our land.

If there are obstacles that block sunlight, you will need to work with the home’s positioning to make the most of solar radiation.

3 Slope

The slope, together with the subsoil, are two of the key factors in determining how to know whether a plot of land is suitable for building.

Sloping plots are usually cheaper because the difficulty of construction will later entail additional costs for earthmoving and retaining works.

However, a sloping plot can also be very favourable if the slope faces south. This would allow the house to be well oriented while also protecting us from the climate on the north side.

Finally, sloping plots always allow you to enjoy good views, as obstacles such as vegetation or neighbouring houses are usually at a lower level.

4 Subsoil

When it comes to how to know whether a plot of land is suitable for building, one of the most important characteristics is the composition of the subsoil.

To know the characteristics of the subsoil, it is necessary to commission a geotechnical study before starting the project. However, if the goal is to understand the land before buying it, we can request a trial pit from a geologist—an option that is more affordable than a full study—and obtain key information about the soil type and its bearing capacity, helping us avoid problems later on.

At our sustainable architecture studio in Barcelona, we always accompany you to visit the plot to carry out an on-site assessment of the subsoil type and, in cases where we suspect we may find poor ground conditions, we call the geologist to request a quick trial pit.

To carry out a trial pit, you only need to pay for travel and a couple of hours of the geologist’s work, and the information we obtain is essential for making the purchase decision. Sometimes, the geologist can even tell us what the ground is like from photos we take during the visit with the client.

In this way, the soil type will be essential to confirm whether it is possible to build on it and what type of foundations will be required. We must know what the ground is like—its composition, excavation method, bearing capacity to support the house, and the safety factors that will need to be adopted.

There is a basic classification that will initially indicate the conditions of the ground we are dealing with:

5 Presence of water on the plot

As we have mentioned, the degree of moisture and the presence of water will affect the quality of the ground. If there is a significant presence of water, the foundations will be designed for these conditions and will likely need to be oversized and made more robust.

It will be important to check the soil’s filtration capacity. Cohesive soils tend to filter water more slowly. Therefore, if there is high moisture, we will need to work with water collection and drainage systems.

On sloping plots, we will have the advantage of the incline to help drain water away.

Another characteristic to ensure is that the plot is not in a flood-prone area and that there is no nearby river. Otherwise, if water can accumulate on our land during certain periods, it will be necessary to plan for an elevated home or one capable of withstanding contact with water. This would complicate and increase the cost of construction.

To know whether there is water in the subsoil of our plot, there is no alternative but to commission a full geotechnical study, which can be carried out without issue after purchasing the land, as the presence of water will not be decisive in the purchase decision.

On the other hand, in addition to the geotechnical study, there is the possibility of carrying out a geobiological study. A geobiological study detects, through various means, naturally occurring influences such as ground fissures or underground water currents that may cause geopathy. Geopathies are geomagnetic currents that can affect the wellbeing of the home’s occupants.

6 Possible impacts from electrical or magnetic radiation

To know whether a plot of land is suitable for building, you must look not only at the physical characteristics of the land, but also at any external impacts that may exist.

Spanish legislation is very permissive when it comes to levels of electrical and magnetic pollution. Even so, as many studies and government bodies show, it is advisable to avoid overexposure to these waves, as they are harmful to health.

For this reason, it is advisable to keep away from high-voltage towers and power lines, which produce electrical radiation, as well as mobile phone antennas. In general, a minimum distance of 100 to 200 metres is recommended, depending on the power of the line.

7 Urban planning and building regulations

The regulations affecting a plot are equally important for understanding the feasibility and building possibilities on a piece of land. First, we must check the buildability and the permitted site coverage.

When we talk about buildability, we mean the total floor area that can be built, distributed over one or more storeys. On the other hand, site coverage indicates the area that can be occupied at ground level relative to the total plot. If the site coverage on a 600 m² plot is 25%, we can occupy a maximum of 150 m² at ground level. With regard to a home, we should also check how many storeys can be built and the permitted number of parking spaces.

On sloping plots, it will be important to consult the regulations regarding earth retention. Depending on the municipality, the volume of earth that can be moved or the height of retaining walls may be limited. These regulations usually exist to avoid major visual impacts.

Regulations may also determine the construction materials, especially for sensitive elements such as the façade.

Recently, we encountered a case where regulations require the house to be clad in stone, as we are in a town whose historic architectural fabric has traditionally been built in stone.

This is the project for Casa Colomers, where the structure is built in timber and clad in stone—a solution that performs very well climatically.

Likewise, the boundaries with neighbours and the street may be defined in terms of material or height. Generally, a minimum distance of around 3 to 6 metres from the street boundary or neighbouring plots must always be respected. In addition, it will be necessary to confirm with the town hall that utilities are available: water, gas, sewerage, electricity, or even fibre optic. There are areas where they may not be available. In that case, alternatives would need to be sought or the home would need to operate self-sufficiently.

Finally, if the plot is located within a residential development, we should check with the town hall that it has been adopted. Otherwise, it is the residents who have to take care of repairs and maintenance of the outdoor and public areas. This would be the case for private developments. In the worst case, a non-adopted development may be the responsibility of no one, and therefore the town hall may not grant building permits.