Important parameter in the land-use plan
In order to calculate the maximum constructible area for your property the land-use plan of the municipality is required. The form and the size of the constructible area, the gross floor area, the usable space and the number of floors can be established via the parameters included in the land-use plan.
Essentially, the land-use plan includes the following values:
- land-use type (e.g. Commercial construction, residential construction)
- Type of area (residential area, mixed use area, commercial area…)
- Land area
- Floor space ratio
- Coverage ratio
- Building lines for the property
- Building alignments
- Number of possible story propers (is regulated by the state building regulations)
- Roof shape
- Roof pitch
- Ridge line and eave
- Information about adjoining buildings, garages and parking spaces
Establishing the gross floor area, the constructible base area and the story propers:
The following parameters provide a basis for the following calculations. (You can actually find these building lines for the property – building alignment values in the land-use plan.)
- Land area: 500 m²
- Floor space ratio: 0.5
- Coverage ratio: 0.25
- Number of possible story propers: 2
Calculating the gross floor area:
The gross floor area is the total amount of all possible story propers plus partial stories (such as basement and attic floor)
- In case of the story propers, the area surrounded by the external walls including the wall thickness of the external walls is relevant.
- In case of the attic floor, the specific part of the room slopes has to be deducted from the gross floor space which falls below a ceiling height of 1.50m. The thickness of the external walls has to be added to the calculation.
- The basement is included only if it is completely or partially approved as a habitable or working room. In this case the thickness of the external walls has to be added to the calculation as well.
In case of a gross floor area of 500m2 and a floor space ratio of 0.5, the gross floor area is 500m2 x0.5=250m2.
Calculation of the constructible land area:
In case of a gross floor area of 500m2 and a floor space ratio of 0.25, the value for the constructible land area is 500m² x 0.25 (coverage ratio) = 125 m². Remark: The constructible land area can also be limited to a smaller size by building lines, setbacks or a building window in the land-use plan. .
Calculation of the number of floors:
The number of possible story propers is calculated based on the gross floor area and the value for the constructible land area. In our example, this is 250 m² (gross floor area) /125 m² (constructed land) = 2 story propers. This value must not exceed the number of possible story propers in the land-use plan. Remark: Basement and attic floors are usually not considered as story propers. The state building regulations regulate in which case a floor is actually a story proper.
You can find additional articles helping you plan your house in our guidelines for house builders.
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