Building class

Building class is a classification of buildings under building regulations into five categories (GK 1 through GK 5) based on height and use, as defined in the Model Building Code (MBO) and the state building codes. The building class determines the requirements for fire protection, structural stability, escape routes, and building materials. The higher the building class, the stricter the technical requirements. For builders, architects, and owners, the correct classification of a building into the appropriate class is crucial for planning and approval procedures.

The Five Building Classes According to BayBO

The Bavarian Building Code (BayBO) distinguishes the following building classes in Art. 2, Para. 3:

GK 1 - Detached Buildings:

• Detached buildings used for agricultural and forestry purposes
• Other detached buildings with a maximum floor height of 7 m in the highest living space and a maximum of 2 units, each with up to 400 m² of usable floor area

GK 2 - Low-rise buildings:

• Buildings with a maximum floor height of 7 m and a maximum of 2 units, each with up to 400 m² of usable floor area (not detached)

Class 3 - Medium-height buildings:

• Other buildings with a maximum floor height of 7 m (e.g., three-story apartment buildings)

GK 4 - Buildings:

• Floor height of the highest occupied space more than 7 m up to a maximum of 13 m

GK 5 - High-rise buildings and other tall buildings:

• Floor height of the highest occupied space more than 13 m

Significance of the building class for fire protection

The building class forms the basis for all fire safety requirements: fire resistance rating of building components (F 30, F 60, F 90), requirements for stairwells, doors, and escape routes, as well as necessary fire alarm systems and sprinkler systems. In GK 1 and GK 2, significantly less stringent requirements apply, while GK 5 and high-rise buildings require complex fire safety concepts.

Specifically, the following core requirements apply to building classes in Bavaria:

• GK 1 and GK 2: Load-bearing components made of combustible materials are permitted; no smoke exhaust opening is required in the stairwell
• GK 3: Load-bearing walls and ceilings must be at least fire-retardant (F 30); stairwells must be equipped with smoke extraction capabilities
• GK 4: Load-bearing walls and ceilings must be highly fire-retardant (F 60); stairwells must be constructed of non-combustible materials
• GK 5: Fire-resistant structures (F 90); separate fire protection concepts developed by experts

Distinction: Building Class vs. Building Type

Building class and building type are different classification systems, both of which are relevant for a property:

• The building class describes structural and technical characteristics (height, units of use) and determines fire protection requirements
• The building type describes the use (single-family home, multi-family home, commercial) and is relevant for valuation, taxes, and insurance

For example, a five-story multi-family house may be classified as GK 4 (structural and technical) and as a multi-family house (type of use). Both classifications must be taken into account during purchase, renovation, and operation.

Building Class and Real Estate Purchase

When purchasing a property, the building class is noted in the building permit. For subsequent changes (e.g., adding stories, attic conversion, change of use) that would alter the building class, a new building permit is required. Owners of multi-family residential buildings should verify whether the actual building height still corresponds to the approved building class-subsequent additions can alter this unnoticed.

A change in the building class due to an addition or renovation may require the retrofitting of fire safety measures-fire alarm systems, stairwell security, fire-retardant doors-which can incur significant costs. Anyone planning such a measure should consult a fire safety engineer and the building code office in advance.

Practical Tip for Property Owners in Nuremberg and Franconia

Many buildings in Nuremberg’s Wilhelminian-style housing stock are classified as GK 3 or GK 4. Anyone purchasing and modernizing such a building should check early on whether planned renovation measures require fire safety retrofits. In particular, when converting rental buildings into condominiums (establishment of condominium ownership), the building code authority closely examines compliance with the requirements of the respective building class.

In such cases, we recommend involving a fire safety engineer early on to avoid unpleasant surprises. In a specific case in Nuremberg, we encountered a situation where a planned attic conversion would have raised the building’s height to GK 5-which would have required significant fire safety retrofits and made the project economically unviable. Such scenarios must be analyzed before the purchase.

Frequently Asked Questions

Can I determine a building’s height based on its building class?

Not precisely, but approximately. Classes 1 through 3 correspond to buildings with a floor height of up to about 7 meters in the highest occupied space (roughly: up to 3-4 full stories). Class 4 corresponds to about 4-5 stories, and Class 5 covers everything above that. However, the story height varies depending on the building type.

Does the building class affect construction costs?

Yes, significantly. Higher building classes require more extensive fire protection measures, heavier structural components, and more complex building services, which increases construction costs. For new construction, the target building class should be agreed upon with the architect early on to avoid unnecessary additional costs.

Where can I find my building’s class?

The building class is noted in the building permit and the fire safety certificate. For older buildings without current building permit documents, it can be determined based on the actual building height and usage structure. If in doubt, the Building Authority of the City of Nuremberg or the respective municipality can provide information.

What happens if a building falls into a higher building class after a renovation?

In that case, the requirements of the higher building class apply to the new construction or renovated portion. In many cases, the existing structure must also be retrofitted to meet the requirements of the new class-especially regarding fire safety. The Building Authority decides on a case-by-case basis to what extent retrofitting is required. It is therefore strongly recommended to submit a preliminary inquiry to the Building Authority well in advance of any major renovation or addition.

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