What is an above-ground storey?
How many storeys does the building have? For the OIB guidelines that is not a matter of counting but of definition. And the definition has two halves: a rule and an exception. Piloti counts by both halves, with the citation.
Definition from the OIB-Richtlinien, Begriffsbestimmungen, May 2023 edition, in our own translation.
In short
Under the OIB definitions, an above-ground storey is a storey whose external boundary surfaces lie, in total, more than half above the adjoining ground after completion; storeys without dwellings, business units or parts of them, such as unconverted roof spaces, do not count. Piloti counts the storeys for the building class under this definition, with the citation.
Above-ground storey (Geschoß, oberirdisches)
“Storey whose external boundary surfaces lie, in total, more than half above the adjoining ground after completion. Storeys in which there are no dwellings, business units or parts of them (e.g. unconverted roof spaces, machine rooms, rooms for building services) do not count as above-ground storeys.”
How Piloti helps
Piloti counts the above-ground storeys for the building class under this definition, with the citation, and asks when your documents do not show whether a roof space is converted. For an alteration it first classifies the project, and only then the requirement.
The rule: more than half above ground
What decides is the sum of a storey’s external boundary surfaces, not a single facade. On a level plot this is rarely a question. On a slope it is: a storey that stands free on the valley side and sits in the ground on the hill side can be above-ground, even if the drawing calls it “lower ground floor”.
The ground after completion is what counts. Backfill can push a storey below half; excavating for light wells or a terrace lifts it above. Both are shown in the submission drawings, and that is where to check.
The exception: storeys without units
A storey containing no dwellings, business units or parts of them does not count. The definition gives unconverted roof spaces, machine rooms and rooms for building services as examples.
“Or parts of them” is where close reading matters: if even part of a maisonette or an office lies in the roof storey, it is an above-ground storey. A dwelling’s gallery in the roof therefore counts.
Why counting has consequences
- The number of above-ground storeys is one of the values of the building class: no more than three for GK 1 to 3, no more than four for GK 4.
- The highest above-ground storey sets the escape level. An additional storey raises both values at once.
- In an existing building, a roof conversion therefore often changes more than the roof: it can shift the building class and with it the fire safety requirements.
- Building codes and development plans sometimes use their own storey terms for building height and plot development. The OIB definition applies to the OIB guidelines, not automatically to plot development law.
Good to know
Whether a slope storey lies more than half above ground, the design team measures on the elevations; Piloti says which surfaces to compare. If the documents do not show whether a roof space is converted, it asks.
Questions
Is a basement an above-ground storey?
A basement lying mostly in the ground is not an above-ground storey. If its external boundary surfaces lie, in total, more than half above the ground after completion, on a slope for example, and it contains dwellings or business units, it counts, whatever the drawing calls it.
Does a roof storey count as an above-ground storey?
By definition, an unconverted roof space does not count. As soon as the roof storey contains a dwelling, a business unit or even part of one, it is an above-ground storey.
Does a plant storey count?
No, as long as it contains no dwellings, business units or parts of them. The definition expressly names machine rooms and rooms for building services as examples.
Does the OIB definition also apply to the building code?
Not automatically. Building codes and development plans sometimes govern building height and plot development with their own terms and measuring rules. The OIB definition applies to the building class and the OIB requirements; state law applies to plot development.