DIN 277:2021-08 “Grundflächen und Rauminhalte im Hochbau” (the German floor-area standard) lays down how a building’s floor areas are determined and structured. Six quantities form a calculation scheme: the gross floor area (BGF) splits into construction area (KGF) and net room area (NRF); the NRF in turn into usable area (NUF), technical area (TF) and circulation area (VF).
In short
- BGF = KGF + NRF. The gross floor area covers all the area a floor level has – rooms and construction.
- NRF = NUF + TF + VF. The net room area is the area of the rooms, structured by what they serve.
- Category R or S. Each area is also classified by whether it is enclosed on all sides (R) or – like balconies and loggias – not (S).
Definition under DIN 277:2021-08
The standard treats each floor level separately and sums them to the building value. The gross floor area is measured at the outer boundaries of the construction. It splits into the construction area – the floor area of rising components such as walls, columns and piers – and the net room area, the floor area of all rooms in clear dimensions between the component surfaces, measured at the top of the floor finish.
The NRF is structured by use: usable area for rooms serving the building’s intended purpose (seven use categories NUF 1 to NUF 7), technical area for building services and circulation area for access, circulation and escape.
Since the 2016 edition the standard knows only two categories of enclosure: R (standard case) for rooms enclosed on all boundary surfaces – floor, ceiling, wall – and S (special case) for areas structurally connected to the building but not enclosed on all sides. The former threefold division into categories a, b and c has been dropped.
Distinction
| Abbreviation | Name | Contains | Until 2016 |
|---|---|---|---|
| BGF | Gross floor area | KGF + NRF, all floor levels | BGF |
| KGF | Construction area | Walls, columns, piers | KGF |
| NRF | Net room area | NUF + TF + VF | NGF (Netto-Grundfläche, net floor area) |
| NUF | Usable area | Rooms serving the intended purpose, NUF 1–7 | NF (Nutzfläche) |
| TF | Technical area | Rooms for building services installations | FF (Funktionsfläche) |
| VF | Circulation area | Corridors, stairwells, lifts, ramps | VF |
| Category | Meaning | Examples |
|---|---|---|
| R | enclosed on all sides | living rooms, offices, garages with roller door |
| S | structurally connected, not enclosed on all sides | balcony, loggia, roof terrace, covered courtyard, external staircase |
In practice
The question decides which quantity is needed. Cost indicators under DIN 276 refer to the BGF and the gross volume derived from it. Space management, room book and service charges work with the NRF and its parts – above all the NUF, because it shows how much area serves the actual purpose. Rental areas under WoFlV or gif MF-GIF are separate rule sets with their own counting rules.
A floor plan supplies the building blocks of the NRF directly: every room polygon is a net room area once the scale is fixed. The KGF – and with it the BGF – only emerges from the wall geometry. Whether a balcony is covered, and hence how to classify it, often only the section shows.
Normraum relevance
Normraum delivers the net room area per room from the as-built plan: room number, use and area under DIN 277 in clear dimensions, with confidence and source reference in the check log. The allocation to NUF, TF and VF follows the use per room and remains a professional sign-off. The KGF, and with it the BGF, the planner derives from the detected walls – the room book does not report it as a floor value.