Understanding property surfaces in Luxembourg: GBA, NFA, usable, habitable
In Luxembourg, the multiplicity of surface definitions is a frequent source of confusion for buyers, investors and even professionals. Unlike France where the Carrez law imposes a single definition, the Grand Duchy uses several coexisting frameworks:
- Gross Built Area (SCB): total area measured to the outside of walls, including walls, technical shafts and common areas. Used for floor area ratio calculations in PAG/PAP plans.
- Net Construction Area (SCP): area measured inside load-bearing walls, excluding technical shafts but including internal partitions. The reference for construction costs (OAI FC.04).
- Usable Area (SU): actually usable area, excluding walls, partitions, shafts and internal stairs. The most relevant area for comparing dwellings.
- Habitable Area: subset of usable area, limited to rooms used for habitation. Excludes cellars, unconverted attics and garages.
Reference standards: OAI FC.04 and ILNAS 101
Two main standards govern surface measurement in Luxembourg:
- OAI FC.04 (Calculation Sheet No. 4): published by the Order of Architects and Consulting Engineers, it defines measurement methods for construction projects. It distinguishes SCB, SCP, usable area and ancillary areas. This is the reference used by architects for plans and fee calculations.
- ILNAS-EN 15221-6: European standard transposed in Luxembourg by ILNAS. It harmonises surface definitions for facility management, distinguishing Gross Floor Area (GFA), Net Floor Area (NFA) and Net Room Area (NRA).
The correspondence between the two frameworks is not always direct, requiring conversion tables. Our tool integrates the official conversion ratios published by the OAI.
Weighting of ancillary surfaces: cellars, balconies, terraces, garages
In Luxembourg property practice, ancillary surfaces are not counted at 100% of their value. Standard weighting coefficients are:
- Cellars: coefficient of 0.25 to 0.50 depending on ceiling height and fit-out. A converted cellar (height > 2.20m, natural light) is weighted at 0.50.
- Balconies: coefficient of 0.30 to 0.50. A covered balcony is weighted higher (0.50) than an open one (0.30).
- Terraces: coefficient of 0.25 to 0.50 depending on area and aspect. Large penthouse terraces can be weighted at 0.50.
- Private gardens: coefficient of 0.10 to 0.20 depending on location and area.
- Garages and parking: not weighted in habitable area, but valued separately (EUR 25,000 to 50,000 per indoor space).
These coefficients are used to calculate the weighted area that serves as the basis for price per sqm in transactions and valuations.
Tax administration guidelines on commercial surfaces
The Direct Tax Administration (ACD) and the Registration Administration (AED) use specific surface definitions for tax calculations:
- The commercial surface mentioned in notarial deeds in Luxembourg is not defined by a single law. In practice, it generally corresponds to SCP plus weighted ancillary areas.
- For property tax (Grundsteuer), the area considered is usable area including weighted annexes.
- For registration duties, the area stated in the notarial deed is authoritative. It is therefore crucial that the notary specifies the measurement method used.
Our converter allows switching between definitions and applying appropriate weighting coefficients to obtain a surface consistent with the intended use (transaction, valuation, tax, property management).