Volume

Gross Floor Area - Gross floor area refers to the volume of a building in cubic meters and thus describes the total enclosed space bounded by the exterior surfaces of a structure. In the real estate industry, gross floor area is a key parameter for calculating construction costs, the asset-based approach to real estate valuation, and the assessment of a building under building regulations.

Calculation and Normative Basis

The calculation of cubic volume is based on DIN 277, which defines floor areas and volumes of structures. The gross volume (BRI) comprises the total volume of a building enclosed by the exterior surfaces of its structural components-including structural surfaces, plaster layers, and attic space. The calculation is typically performed by multiplying the gross floor area (GFA) per floor by the respective floor height and then adding all floor volumes together.

While the GFA describes only the area of a floor in square meters, the volume additionally accounts for the third dimension. This distinction is important in practice: Two buildings with identical GFA can differ significantly in their cubic volume, for example if one has a higher ceiling height, a converted attic, or a basement. DIN 277 also distinguishes between gross cubic volume and net cubic volume (NRI), which describes the actual usable volume of space excluding structural components.

In the asset-based method of real estate valuation according to ImmoWertV, the volume serves as the basis for determining standard construction costs (NHK). The NHK tables list construction costs per cubic meter of enclosed space, differentiated by building type, year of construction, and standard of finish. A correct calculation of floor area is therefore directly relevant to value-deviations of just a few percent can lead to valuation differences of tens of thousands of euros for larger properties.

Calculating Floor Area in Older Buildings

For existing buildings, particularly older structures without complete architectural plans, determining floor area poses a particular challenge. Often, no scaled floor plans or sectional drawings are available, making on-site measurements necessary. Irregular floor plans, subsequent additions and renovations, vaulted basements, or mansard roofs further complicate the calculation. In such cases, the building is broken down into simple geometric shapes-cubes, prisms, truncated pyramids-whose individual volumes are added together.

Particular care is required when determining value using the asset value method for older buildings. Unheated basements, unfinished attics, and open loggias are weighted differently in the NHK tables. We recommend that the volume calculation for complex existing buildings always be performed by a certified appraiser.

Cubic Volume and Building Law: Building Volume in the Zoning Plan

In building law, building volume plays a supplementary role under the term “building volume.” The building mass index (BMZ) specifies how many cubic meters of enclosed space are permitted per square meter of land area. It complements the floor area ratio (GRZ) and the floor space index (GFZ) and is particularly relevant for buildings with unusually high ceilings-for example, industrial halls, warehouses, or theaters. The BMZ is rarely found in Nuremberg’s zoning plans; it is used where the standard ratios GRZ and GFZ are insufficient to control the desired level of use. Anyone wishing to add a story or expand a building should check whether a BMZ is specified in the applicable zoning plan and whether it still allows for flexibility.

Practical Tip for Nuremberg and Franconia

In the Nuremberg metropolitan region, we encounter volume calculations particularly frequently when appraising Wilhelminian-style apartment buildings with high ceilings and Franconian sandstone houses with thick walls. The room heights typical for Nuremberg-ranging from 3.20 to 3.60 meters in older buildings-result in significantly higher cubic volume compared to modern new constructions with 2.50-meter room heights-and thus in higher property values.

At the same time, the thick sandstone walls of Franconian older buildings are included in the cubic volume, even though they do not constitute usable space. In practice, this means that the property value based on cubic volume can be higher for a Wilhelminian-style older building in Nuremberg than for a functionally comparable new building-even though the actual living space is smaller. Appraisers account for this through adjustments to the NHK. We recommend that owners and prospective buyers always ensure a professional calculation of the building’s volume during a real estate appraisal and compare the results with the available planning documents at the Building Authority of the City of Nuremberg or the respective district offices.

Frequently Asked Questions

What is the difference between building volume and gross floor area?

Cubic volume describes the three-dimensional volume of a building in cubic meters, while gross floor area (GFA) indicates the two-dimensional area of all floors in square meters. Both values are calculated according to DIN 277 but have different applications: GFA is primarily used for area calculation and determining rental space, whereas cubic volume is used for construction cost estimation and the asset value method. Simply put, the cubic volume is calculated by multiplying the gross floor area by the height of each floor.

Why is cubic volume important for real estate valuation?

In the asset value method, the construction costs of a building are calculated using the standard construction costs (NHK) per cubic meter of enclosed space. A precise calculation of the volume is therefore the basis for a reliable asset value. Incorrect calculations directly lead to an overvaluation or undervaluation of the property. The volume has tax implications, particularly in cases of inheritance and divorce, where the tax office uses the asset value.

How accurate must a volume calculation be?

DIN 277 does not specify an explicit tolerance, but in valuation practice, deviations of no more than three to five percent are considered acceptable. For court-ordered appraisals and tax assessments, a higher degree of accuracy is expected. We recommend that, in cases of discrepancies between existing plans and the actual building stock, a current measurement be commissioned to avoid future disputes regarding the building’s value.

Does floor area directly influence the purchase price of a property?

Not directly-the purchase price is a market variable determined by supply, demand, and comparable prices. Indirectly, however, floor area influences the property value used by banks to determine the mortgage lending value and in tax assessments. For a property with a high cubic volume (e.g., due to high ceilings), the mortgage lending value may be higher, which has a positive effect on obtaining a loan. Conversely, a low cubic volume (e.g., in a single-story bungalow with a low roof pitch) can depress the property value, even if the location and living space are attractive.

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