Design Process
What is the buildability of a plot of land?
In today’s article, we will address a very specific concept associated with the urban planning regulations of any plot of land, which will influence our construction capacity on it: buildability. In addition to defining it, we will delve into the history of this concept and its function within the urban logic that structures our environment. We will try to exhaustively clarify what land buildability is.
Urban development potential and buildability
Urban planning analyzes the complex territorial reality of a given moment to generate a series of regulations and concepts that will shape the future of that urban situation. The term ‘urban development potential’ (aprovechamiento urbanístico) dates back to the Spanish Land Law of 1975, the first update after the dictatorship, which began to consider the land’s capacity to generate economic benefits through urban development.
It is also at this point in urban legislation that a distinction began to be made between different types of land: urban, developable, and undeveloped, which we explain in detail in an article on this blog.
Thus, a concept capable of measuring the economic specificities of a plot of land was coined: urban development potential, based on the regulation of buildability and the possible uses of each plot. Based on an exhaustive study of the current situation, regulations are established that will define the degree of development potential of a plot in the future, in order to control its value in the real estate market. This system is structured through a division by zones, which will delimit the different municipal plans, i.e., specific regulations for each municipality.
Based on the zone, we will determine its buildability percentage and its future use. However, if the land type is undeveloped, meaning it cannot be built upon, the degree of buildability will not be established, but a specific use will be, whether for housing, industrial, private equipment, etc. Based on this buildability and these uses, the amount of land to be allocated to ‘systems,’ i.e., public facilities, is calculated. Broadly speaking, this is how urban planning logic is structured in Spain.
What is the buildability of a plot of land?
But let’s return to the key question of the article: what is the buildability of a plot of land?
Land buildability is described as the simple equation of X square meters of floor area that can be built on X square meters of land.
That is, the total amount of square meters that can be built on a plot, whether on one or several floors.
Within this definition, two types of buildability are distinguished: gross or zonal buildability and net buildability, both established by municipal or regional regulations.
Gross buildability
Buildability is referred to as gross or zonal if it relates to an area subject to urban planning, meaning it corresponds to a land area that will undergo urban transformation in the future.
This type of buildability usually affects what is known as developable land, a transitional land regime. It typically consists of land with rural characteristics, which would normally fall under the undeveloped land regime, but which, through urban studies of territorial evolution, is foreseen as susceptible to being incorporated into the urban area of the city through an urbanization process.
For this reason, it remains developable land until it is transformed into urban land through a Partial Plan or Reparcelling Project, at which point its regime becomes that of urban land.
There are two subgroups within the developable land category: sectorized or unsectorized developable land. The difference depends on whether it is considered land that must or may be subject to urbanization. The former is called sectorized developable land, and the latter, unsectorized developable land.
Net buildability
On the other hand, net buildability refers to developable plots with detailed planning that establishes their building conditions.
Following the definitions we have provided so far regarding the different types of land, net buildability corresponds to plots under the urban regime, i.e., within the existing city.
The basic criterion for classifying land as urban is that it is located in an urbanized area, meaning it has the basic urban services typical of this type of land – road access, water, sanitation, and electricity.
Comparative example of the buildability of two plots of land
For this reason, when we are going to buy a plot of land, regardless of its total square footage, we are truly interested in knowing to what extent we will be able to build on it.
Let’s look at the difference with an example:
Suppose we have a 1,000 square meter plot with a buildability of 0.25 m2 of floor area/m2 of land and another of 600 m2 with a buildability of 0.40 m2 of floor area/m2 of land.
We perform the following calculations:
Plot 1: 1,000 m2 x 0.25 m2 of floor area/m2 of land = 250 square meters of buildable area.
Plot 2: 600 m2 x 0.40 m2 of floor area/m2 of land = 240 square meters of buildable floor area.
We conclude that in the case of the second plot, we can build almost the same area as on the first.
Beyond whether, from a design perspective, we are more interested in having a larger outdoor area for a garden or pool, the conclusion is that a larger initial surface area of a plot is not always synonymous with a greater number of buildable square meters. Therefore, we must be aware of how urban planning legislation will condition our building possibilities.
Factors influencing the buildability of a plot of land
In addition to this practical example we just saw, there are a number of other factors that also influence the calculations. We will list them below:
1. Uses permitted by planning
2. Location
3. Building conditions
3.1. Street and building alignments
3.2. Regulating height
3.3. Buildable depth
3.4. Setbacks
1. Uses permitted by planning
In urban development potential, the other essential variable considered, in addition to buildability regulations, is the uses permitted by planning, since the value of the building varies according to the uses to which it can be destined.
For example, the value of floor area that can be used for housing is usually different from that for industrial uses. In principle, buildability with a wide range of possible uses, such as housing, tends to achieve higher value compared to that with more restricted use alternatives, such as industrial or private equipment use.
Thus, depending on the permitted use and building typology, the most common buildability values are as follows:
In single-family housing areas, buildability can reach up to 0.75 m2 of floor area/m2 of land in older, small-plot zones; while in others, i.e., larger plots, the normal range is 0.3 – 0.5 m2 of floor area/m2 of land. On the other hand, multi-family housing areas are assimilated with office buildings and allow values ranging from 0.5 to 1.5 m2 of floor area/m2 of land. Finally, economic activity areas, with dominant ground floor typologies, usually range from 0.8 to 1.2 m2 of floor area/m2 of land.
However, such value differences are not stable but vary according to the location of the plots based on real estate market conditions in each territory, as we will see in the next point.
2. Location
The location of a plot is another factor influencing its regulating buildability values, as similar buildings with similar use possibilities can vary greatly in value depending on their location within the same city.
Again, generally, a more urban environment tends to be regulated with higher buildability, with this value potentially exceeding 1 m2/m2 of land, always in the case of urban land. In developable land zones, buildability usually ranges from 0.2 to 1 m2 of floor area/m2 of land, while in rural areas it tends to be even lower due to more available space for construction.
3. Building conditions
Building conditions generally tend to be less important than the previous variables and, at times, can be considered implicit within them. However, it is clear that two plots with the same buildability, the same uses, and a similar location in the city can have different values. This depends on the difference in quality that can be obtained due to the various building conditions set in each case, for example, in a closed block or in detached buildings with a garden.
In urban planning, there are three basic systems for building arrangement: by street alignments, by detached building on a plot, and by volumetric definition. In this section, we will discuss the urban parameters derived from the street alignment system, whose volume is established based on a regulating height and a maximum depth. The usual pattern for these buildings is to occupy the full width of the plot along the street front.
This refers to the typical urban block between party walls that forms a continuous street front, an architectural style with significant compositional limitations but especially present in the characterization of urban space.
This alignment system is the most prevalent in the older urban fabrics of our cities. It is a system that originated in the Middle Ages, in the most elemental way cities were built: by aggregation of buildings. Subsequently, the system was rationalized through the definition of new street layouts and the organization of existing fabrics formed according to its logic.
3.1. Street and building alignments
Basically, it involves defining the position of the line that defines the facade plane of buildings and marks the boundary between public and private space. Alignments are determined in the planning maps that usually configure the blocks, which are typically designed to be enclosed by a strip of building around their entire perimeter.
3.2. Regulating height
Just as we ask what land buildability is, let’s examine to what extent regulating height can influence this concept and the configuration of any construction.
We define regulating height as the maximum height in meters that a building can have, which is usually established based on the street width and corresponds to a specific number of permitted floors.
Its relationship with land buildability stems from the fact that, depending on the permitted height, the total buildable square meters on the plot will be distributed in one way or another. In some cases, especially in historic urban fabrics, the height may not be maximum but mandatory, to achieve continuity in the cornice lines of street sections.
For all these reasons, it is important, before buying a plot of land, to consult with the municipal technician about the point from which the maximum height is measured, if this information is not in the regulations. This is especially important for sloping plots, as measuring height from the street is not the same as measuring it from the midpoint of the total slope of the land. There are cases where the owner, along with their architect, is allowed to measure the height from where construction begins.
3.3. Buildable depth
Buildable depth is the width of the plot strip, measured from the street alignment, that can be built upon at the regulating height. As we can see, this is a planning condition that refers to the blocks typical of an urban fabric, so it is not usually established for detached buildings on plots, which we will discuss later.
In the city, buildable depth forms a crown around the perimeter of the block, defining an interior space, which is the inner courtyard of the block, whose area may or may not be buildable at ground level. The intention of this regulation is to ensure dwellings that allow for two facades capable of cross-ventilation, since one facade faces the street and the other the block courtyard. Typical depths range between 12 and 20 meters, as beyond 14 meters, it is difficult to design properly functioning dwellings between party walls.
However, a detached house on a plot usually enjoys 4 facades with different orientations, so it does not pose a problem regarding depth.
3.4. Setbacks
Setbacks are the minimum or maximum distances that must be left from the plot boundaries, thus representing a space that we must consider when planning the size and position of our home relative to the plot.
Generally, a setback from a neighbor is not the same as from a front or even a rear part of the plot, so they are differentiated in the regulations. Especially in dispersed urbanizations, the distance from the street facade front is greater than the separation from neighbors.
In contrast, in urban plots, we may find that regulations require us not to leave any distance from either the street or the neighbor.
Furthermore, because the line marking the buildable depth is not normally considered an alignment, but rather a limit that the building cannot cross, an interior setback will always be possible, although it may be of little interest, as it entails a quite significant loss of floor area in the urban fabric.
In any case, voluntary setbacks will make sense if the project has the possibility of arranging the buildability it loses by reducing the width or depth of the building in another way.
A specific case: detached building on a plot
The second of the three basic systems for building arrangement is the case of detached building on a plot, which is normally associated with single-family housing projects. In fact, the three building arrangement systems – aligned with the street, detached on a plot, and by volumetric definition – correspond to three distinct and clear logics, each with specific parameters that result in urban fabrics with well-defined characteristics.
For all these reasons, in this section, we will discuss urban parameters that may be minority, but are specific to this type of system, such as plot division, occupancy, distances to boundaries, fences, maximum building area, and auxiliary buildings. Like everything, it is not an exact science, as hybrid systems exist that encompass conditions from different systems. Thus, municipal regulations will always prevail, establishing the variables for each plot.
In this planning system, the building relates more to the plot than to the street, from which it maintains a separation. These types of urban fabrics are usually less dense than those with street alignment, where the perception of buildings is accompanied by that of the plot’s open areas, with trees and landscaping.
It is for this reason that, in the case of detached building, understanding what land buildability is becomes more important when designing our future home and, of course, the prior step of purchasing the land, since both buildability and plot division (shape and dimensions of the plot) are determining factors.
Plot division
As we have said, the dimensions and shape of the plots are determining factors of the character of the urban fabric. Hence, building regulations establish the conditions for plots to be considered buildable: minimum area and minimum frontage are the most frequent.
The definition of maximum plots also makes sense to avoid excessively large buildings, although the size of buildings that can be constructed can also be directly limited, which forces the fragmentation of buildings on large plots into several buildings or units.
In single-family housing areas, the different planning zones are usually defined by the minimum plot size established in each, with 250, 400, 800, and 1,000 m2 being common. On the other hand, in multi-family housing and economic activity zones, minimum plots are usually not less than 800 or 1,000 m2.
Occupancy
Occupancy is defined as the percentage of the plot that can be occupied by the building, and its objective is to ensure a certain proportion of free plot area. Additionally, it also serves to establish an occupancy limit for elements without above-ground volume, such as basements, swimming pools, or paved areas.
This is a concept susceptible to being confused with buildability, so in addition to explaining what land buildability is, we will develop a specific article on the blog about the definition of occupancy and its difference from the concept of buildability.
Other parameters to consider
The following parameters are less important, as, as we have said, the plot and buildability are the basic determinants of the characteristics of the detached fabric. However, they are necessary to ensure a certain homogeneity in the relationship between architecture and the plot.
Distances to boundaries: these are strips marked around the entire perimeter of the plot that cannot be encroached upon by any building element – except for exceptions such as parking areas or auxiliary volumes, which are defined in each municipal regulation – in order to guarantee its detached nature.
In detached plots on the periphery, it is common to establish a minimum strip of 3 meters, which is usually increased to 5 meters on the street-facing facade and at the rear of the plot. However, in the case of plots in urban centers, this regulation loses meaning, as it falls under the ‘street alignment’ system where alignment with the street and neighbors is mandatory. Therefore, only a minimum distance from rear courtyards can be established.
Fences: in this planning system, the most prominent element on the street is the plot fence. Therefore, urban planning regulations may establish rules to achieve a certain coherence in the adopted solutions. The rules may refer to the opaque or transparent nature of the fence, its heights, and the materials used.
Maximum building area: to prevent excessively large buildings from being constructed on very extensive plots, which would break the homogeneous grain of the urban fabric, limits can be established on the total floor area of a building. This measure may, in such cases, necessitate the distribution of the floor area into several separate bodies.
Auxiliary volumes: in cases of plots of a certain size, for example from 1,000 m2 upwards, it may make sense to regulate the possibility of auxiliary volumes independent of the dwelling and not for residential use, such as a tool shed. These are volumes that are not considered included in the general buildability of the plot.