Under DIN 277:2021-08 the gross floor area (BGF) is the sum of the floor areas of all floor levels of a building – including the construction. It is the standard’s largest area quantity and consists of construction area and net room area: BGF = KGF + NRF. Measured at the outer boundaries of the components, storey by storey.
In short
- The BGF counts rooms and construction; the net room area counts only rooms.
- Determined per floor level, separately for categories R and S, and summed to the building value.
- The WoFlV has no BGF: it assesses a dwelling’s floor areas under its own rules.
Definition under DIN 277:2021-08
Decisive are the outer boundaries of the construction at the top of the floor finish – the outer edge of the external walls including cladding. Within this boundary lies all that makes up the floor level: the construction area of walls, columns and piers and the net room area of the rooms. Areas serving only maintenance, inspection or repair are left out.
The standard requires the BGF to be reported separately for category R (enclosed on all sides) and category S (structurally connected, not enclosed on all sides). A loggia thus raises the BGF, but in its own column.
Distinction
| Quantity | Includes construction? | Measuring rule | Rule set |
|---|---|---|---|
| BGF | yes | outer boundary of the construction, per floor level | DIN 277:2021-08 |
| KGF | construction only | floor area of the rising building components | DIN 277:2021-08 |
| NRF | no | clear dimensions between the component surfaces | DIN 277:2021-08 |
| Living area | no | floor areas of the dwelling, counted under § 4 | WoFlV (2004) |
In practice
The BGF is the reference quantity of cost planning: cost indicators under DIN 276 are kept in euros per square metre BGF, and the gross volume builds on it. Anyone comparing cost estimates must therefore know whether a BGF with or without category S is meant. The “Geschossfläche” of planning law (the floor space ratio area under § 20 BauNVO) is a different quantity with its own measuring rule and must not be confused with the BGF.
The WoFlV does not ask how large the building is, but which floor areas belong to a dwelling and how they are counted (§§ 2–4 WoFlV). There is no “gross floor area under WoFlV”; whoever uses the term means DIN 277. From a floor plan, the BGF can only be formed with the complete wall geometry – room areas alone are not enough.
Normraum relevance
Normraum calculates the net room area per room under DIN 277 from the as-built plan and delivers the detected walls with source reference in the plan. The room book does not report the BGF as a floor quantity including the construction area; the planner derives it from room areas and wall geometry. The check log documents per room the geometry and confidence behind it.