How are unpaired terraces defined

Base area number: How you calculate it and what it means

The base area number (GRZ) of a property is usually shown in the applicable development plan. The GRZ tells you what proportion the house can have on your property, because it is rare that the entire area can be built on. After all, clearances to the neighbors must be maintained and a place for the garden is usually also provided.

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How is the GRZ calculated?

The base area number is given as a decimal number. 0.2 means that you can build on 20 percent of your property. A 1.0 would represent a complete development.

If there is a GRZ of 0.2 for a 600 square meter property in a development plan, you have to multiply the property size by the GRZ to find out how big your house can be.

Formula: property size x base area number = permissible base area

600 square meters x 0.2 = 120 square meters

In our example, you can build over 120 square meters of your property. However, this does not necessarily mean that the entire area may only be 120 square meters. Because if the development plan allows several floors, the total living space can of course be larger.

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What does everything belong to the base area?

In order to roughly calculate the allowable buildable area of ​​your dream house, you only need the exact size of the property and the specified GRZ.

However, the exact calculation is more complicated. Your architect or property developer will do this for you. Because the buildable area not only includes the house with its outer walls, terraces, balconies and basement exits (also called GRZ I), but also the areas of parking spaces and their entrances, garages, paths, garden houses, oil tanks, ancillary systems and underground structures (also GRZ II).

Often, building owners are allowed to exceed the permitted floor space by 50 percent in favor of such ancillary areas. The GRZ must not exceed 0.8. Since there are major differences in the different federal states and also in the applicable development plans, it is absolutely advisable that you inquire about the local conditions at your local building authority.

What is the GRZ important for?

From an economic point of view, the GRZ is particularly important for sellers and buyers of land and used real estate. The higher the base area, the more valuable the property is.

As a seller you can achieve a higher price and as a buyer you have the opportunity to create more living space per square meter of property. The base area number is therefore one of the most important key figures for assessing the structural use of a property.

But the GRZ is also important for buyers of used property. Namely when you are planning extensions, garages or other outdoor facilities. Depending on what percentage of the permitted floor space has already been used by the existing building, structural expansion is permitted or not.

However, the GRZ also has an urban and ecological significance and is therefore an instrument of urban planning. After all, it ensures that a residential area or a district is not concreted over and that enough open space remains. They are not only important for having enough green space in terms of species and nature conservation, but also for the infiltration of rainwater.

And ultimately the cityscape also benefits from green front gardens and light and air between residential buildings. If you take all the area numbers together, you get an impression of the density of buildings in a municipality. A GRZ of 0.2 is a typical value for a green residential area.

Other key figures for the possible development: The floor area number (GFZ)

In addition to the question of how much area you can build on, how high you can build is also decisive for the use of your property. In addition to the GRZ, the floor area number (GFZ) also defines the maximum amount of living space that can be created.

The GFZ indicates the height of a building and reveals how many square meters of floor space you can build per square meter of property. Attention: The number of floors does not regulate how many floors your house can have.

The maximum floor area for new buildings is in most cases 1.0 to 1.2. In the case of high-rise buildings, on the other hand, the GFZ can be significantly higher.

You can also find this key figure in the development plan. But it also happens that the maximum number of full storeys is already a number in the development plan. Otherwise the following formula applies:

Property size x floor area number = permissible total floor area

If the GZF for a 600 square meter property is 0.5, then the total floor area allowed is:

600 square meters x 0.5 = 300 square meters

So you can build a house on the property, the floors of which have a gross floor area of ​​up to 300 square meters. So, for example, you can build two floors with 150 square meters. Or, if that's allowed, even three levels of 100 square meters each.

From an urban planning point of view, setting low numbers of floor areas prevents too many high buildings, which rob the neighbors of light and thus a part of the quality of life.

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