Building Regulations: Plot Occupation, Usage, and Height

Posted on Nov 11, 2024 in Geology

BUILDING IN THE PLOT

TERMS OF POSITION AND OCCUPATION

Almost always, the freedom of building positioning on a plot is limited by planning regulations. These regulations are based on parameters such as planimetric and altimetric references, the building’s elevation, and its relationship to other buildings.

Planimetric References

  • Boundaries: These define the plot’s limits.
  • Alignment (Public): A line established by urban planning to separate land for highways or public spaces from private plots. It often coincides with the plot’s boundaries.
  • Alignment (Private/Inner): A line separating the buildable area from the free space within the plot. The building must be placed between this alignment and the external alignment. This is also known as the buildable area.

Altimetric References

The most important altimetric reference is the concept of ground level, which is the longitudinal profile of the public highway. It’s crucial for understanding concepts like building below or above ground and referencing the depth of urban services. Benchmarks set by the ground level are used to determine the maximum allowed building height.

Building-Specific References

  • Facade Plane: Vertical planes separating the built area from the unbuilt area. They include all elevation elements except authorized projections like balconies, terraces, eaves, and cornices.
  • Mediatrix: A parameter shared with adjacent buildings, whether attached or detached, that separates plots. When facades cannot fully accommodate protruding elements, aesthetics should be considered.
  • Building Line: The intersection of the ground floor facade with the plot.
  • Setback: The distance between the building line and the external alignment, measured perpendicularly. This concept can also apply to any plot boundary, often called boundary separation, which usually has a minimum required value.

Applying these concepts determines the building’s movement area, which is the portion of the plot where construction can occur.

  • Footprint: The area within the projection of the facade planes onto a horizontal plane.
  • Occupied Area: The area of the plot that can be occupied by the building. The maximum occupancy ratio is the ratio between the maximum occupied area and the total plot area, usually expressed as a percentage.

If the movement area is larger than the occupied area, there’s flexibility in building placement. The occupied area must always be equal to or greater than the building’s footprint, even if regulations allow otherwise. The footprint can be placed anywhere within the movement area, while the occupied area can be placed anywhere within the plot (though it usually occupies the entire area). These parameters ensure a minimum free space on the plot, with exceptions for specific constructions like underground buildings.

BUILDING AND USE AS BASIC PARAMETERS

Building size on a plot is limited by parameters like buildable area and usage.

  • Total Floor Area/Built-up Area: The total built surface of all floors.
  • Buildable Land: The value set by municipal ordinances to limit the total built surface on a plot. This can be determined through a floor area ratio or by considering factors like position, shape, height, and building volume.
  • Floor Area Ratio: The relationship between the total buildable area and the plot area. It can be net or gross, depending on whether it considers the net or gross buildable area.

TYPES OF SURFACES IN A BUILDING

  1. Usable Area: The area suitable for living or, in non-residential buildings, for the intended use. Walls must be at least 1.5m high for an area to be considered usable. Examples include living rooms, terraces, and penthouses, excluding walls and pillars.
  2. Built Area: Defined by the building’s outer perimeter, including walls and partitions. Open terraces are usable but not included in the built area. Holes larger than 0.25 square meters are excluded (e.g., elevator shafts). Open porches/terraces are considered 50% built if covered, and 100% if open on two sides or less. Cutouts must be considered for built area calculations. It’s calculated per floor and includes general elements like housing and commercial premises.
  3. Computable Area: The area considered for building regulations. It may differ from the built area, depending on local regulations. For example, utility rooms are usually built but not computable.

BUILDING HEIGHT

The building’s vertical dimension above ground, expressed in metric units or the number of floors. Regulations specify the origin or reference point for height measurement and the part of the building to be measured. Different parameters are used when height is expressed in metric units:

  1. Cornice Height: Measured to the intersection of the underside of the top floor’s roof slab with the facade plane.
  2. Coronation Height: Measured to the highest point of the roof’s protective elements.
  3. Overall Height: The building’s maximum height, usually up to the ridge.
  4. Height by Floors: Determined by planning regulations for each locality.

Projections over the street are considered in height calculations. The minimum height above the street is usually around 3.5m. Constructions like stairwells, elevator booths, and storage rooms are often allowed above the maximum height (usually coronation). Only chimneys, ventilation systems, and solar panels are typically permitted above the maximum allowed height.

  • Floor Height: The vertical distance between the upper surfaces of consecutive floors.
  • Story Height: The vertical distance between the upper surface of a floor and the underside of its roof slab.

BUILDING FLOORS

  1. Basement: Over 50% of its surface has its roof below ground level.
  2. Semi-basement: Over 50% of its surface has its floor below ground level and its roof above ground level.
  3. Ground Floor: Over 50% of its surface is at or slightly above ground level.
  4. Mezzanine: Its entire surface is between the ground floor and the ceiling of the floor below.
  5. Upper Floor: Any floor above the roof structure of the ground floor.
  6. Penthouse: The top floor with a smaller built area than other floors and setbacks from the main facade.
  7. Attic: Located between the top floor’s ceiling and the underside of the roof’s structural elements.

USES

  • Residential: Intended for housing.
  • Tertiary: Includes buildings providing services to the locality, such as:
    • Offices: Can be in low-rise buildings or combined with housing.
    • Businesses: Require wide streets and proximity to transportation. Plot suitability depends on access (especially for large businesses).
    • Government Buildings: Schools, hospitals, etc., planned according to community needs. Municipalities often allocate land for these purposes, guided by land laws. A percentage of the net plot area is usually designated for public use, often through a loan to the developer.
    • Industrial: Planned in areas where industrial activity minimizes disruption to the city.
    • Green Areas: Usually included within tertiary or community use zoning. They are typically local in character and provided to the council for free.

PATIO

Any unwalled space within a building or any unbuilt space within the outer alignments surrounded by the building. Unbuilt spaces are often called free space. Patio dimensions are generally determined by the height or the number of openings (windows, doors) facing it. More openings usually require a larger patio. Different types of patios include plot patios, English courtyards, and garden patios.