Building Use Classes in BYKHY and Their Impact on Design

Under the Turkish Regulation on Fire Protection of Buildings (BYKHY), buildings are divided into ten classes according to their use (BYKHY Article 8(1)), and this single decision determines everything from compartment area to escape design. If the class is written wrongly, the design is wrong even if every subsequent calculation is done correctly. In case of doubt, the decision of the Ministry of Environment, Urbanisation and Climate Change is followed (BYKHY Article 8(2)).

The most common mistake on site is writing the class list freely. "Healthcare building" and "educational building" are not separate use classes; both are sub-headings of institutional buildings (BYKHY Article 11). This article covers how the classes appear in the text, which design item each class drives, and the strictest-class rule in mixed use.

The ten classes of Article 8

The Regulation lists the classes as follows (BYKHY Article 8(1)): residential buildings, accommodation buildings, institutional buildings, office buildings, commercial buildings, industrial structures, assembly buildings, storage facilities, high hazard places, mixed-use buildings. The scope of each is defined in separate articles:

• Residential buildings are classified by the number of independent units: one- and two-family houses with at most two independent units, and apartment buildings with three or more independent units (BYKHY Article 9).
• Accommodation buildings include hotels, motels, thermal facilities, holiday villages and guesthouses, campsites and student dormitories (BYKHY Article 10). The fact that a dormitory is in the accommodation class is the point most often missed on school campuses.
• Institutional buildings are defined under three sub-headings: educational facilities, healthcare buildings, and remand, prison and correctional buildings (BYKHY Article 11(1)). On the education side the criterion is time-based: buildings used for education by six or more people for 4 hours or more a day, or for more than 12 hours a week, fall within this scope (BYKHY Article 11(1)(a)). On the healthcare side the criterion is the number of beds: buildings in which four or more people can be accommodated as in-patients (BYKHY Article 11(1)(b)).
• Office buildings include places such as banks, stock exchanges, public service buildings and doctors' surgeries (BYKHY Article 12); commercial buildings are sales premises such as shops, markets, arcades, wholesale markets and repair shops (BYKHY Article 13); industrial structures are factories and structures for processing, assembly, packaging, storage, distribution and repair operations (BYKHY Article 14).
• Assembly buildings are buildings where 50 or more people can gather for reasons such as ceremonies, worship, entertainment, eating, drinking, transport and waiting for vehicles (BYKHY Article 15(1)). Article 15(1) lists eight sub-headings: eating and drinking facilities, entertainment venues, museums and exhibition spaces, places of worship, sports areas, terminals and stations, airports, and ports.
• Storage facilities are warehouses and car parks (BYKHY Article 16(1)).
• High hazard places are places where flammable and explosive substances and fuels are manufactured, stored, filled and emptied, and sold (BYKHY Article 17(1)).
• Mixed-use buildings are regulated by a separate article (BYKHY Article 18).

The 50-person threshold for assembly buildings is important (BYKHY Article 15(1)): as soon as a dining hall or conference room in a building becomes suitable for 50 or more people to gather, it counts as an assembly part. Parts suitable for fewer than 50 people to gather are subject to the use classification of the main building (BYKHY Article 15(2)).

Small parts are not a separate class

The Regulation sets an "absorption" rule for small ancillary uses within a building. The same logic repeats in four places:

• Parts used for office services within another building are subject to the use classification of the main building (BYKHY Article 12(2)).
• Small commercial parts in a building that falls mainly in another use class are subject to the provisions of the building's main use classification. Conversely, office, storage and service parts in the same building that are used in connection with the sale of commercial goods fall within the commercial building class (BYKHY Article 13(2)).
• Parts of any building used for assembly but suitable for fewer than 50 people to gather are subject to the use classification of the main building (BYKHY Article 15(2)).
• Storage parts smaller than 50 m² inside a building are accepted as part of the main building (BYKHY Article 16(2)).

The class sets compartment area and hazard class

The first concrete consequence of the use class is the compartment area: the maximum compartment area required in buildings is given in Annex 4 (BYKHY Article 24(6)). Annex 4 sets the areas directly by the Article 8 classes and contains notes that the area may be doubled, or may be unlimited, if suitable fire control systems are installed. The values by class and the conditions of this flexibility are tabulated in the articles on fire compartment areas and on the relationship between sprinklers and compartments.

The second consequence is the hazard class. The hazard class is determined according to the characteristics of the building and the nature of the processes and activities carried out in it; if materials with different hazard classes are present in different parts of a building, the water and pump capacity is determined according to the highest hazard classification of the building (BYKHY Article 19(1)). When forming extinguishing systems and compartments, the distinction between low, medium and high hazard places is used; low hazard places are places containing materials with low fire load and combustibility, with at least 30 minutes of fire resistance and no single compartment area larger than 126 m² (BYKHY Article 19(2)(a)).

The last row of the table is often missed: the fire resistance periods of building elements are given in Annex 3/C according to building use classes (BYKHY Article 29(7)(c)). So the use class determines not only the area but also how many minutes a wall must withstand.

To go deeper by class, see the articles on fire protection in hospitals, fire protection in schools and dormitories, fire protection in shopping centres and fire protection in car parks.

The strictest-class rule in mixed use

Article 18 is a single sentence, but it writes half of design practice: if a building has parts subject to two or more use classifications, and these parts cannot be separated from each other by a fire separation suitable for the higher hazard class, or it is not possible to apply separate protection measures because they are intermingled, the rules of the classification requiring the higher protection measures apply to the whole building (BYKHY Article 18).

The logic of the sentence is this: if separation is possible, each part is designed according to its own class. If separation is not possible, the building is treated as a single unit and the strictest class applies. So in mixed use the real question is not "which class?" but "can the separation really be achieved?"

For the separation to be achieved, the separating element must work as a compartment envelope; the fire resistance of the elements enclosing the compartment must also be continuous at junctions, and there must be no openings without fire resistance between compartments (BYKHY Article 24(7)). A wall with unsealed service penetrations, two spaces joined through a common ceiling void, or a door left open does not count as "separated" in the sense of Article 18.

At this point Article 19(1) and Article 18 must be read together: where separation cannot be achieved, not only the passive measures but also the water and pump capacity are determined according to the highest hazard class (BYKHY Article 19(1)). So in mixed use a separation that cannot be achieved feeds directly into the pump and tank volume.

The cost of a change of use

A change of use class rewrites every threshold without touching the building at all. In existing structures this has a separate consequence: structures that, through a change of use, become healthcare buildings, residential healthcare institutions, nursery schools, crèches, children's clubs, primary schools, children's homes, entertainment venues, accommodation buildings or buildings in which hazardous substances are kept are excluded from the existing building regime (BYKHY Article 138(1)), and the provisions in the other parts of the Regulation apply to them (BYKHY Article 139).

Typical examples: an office floor converted to a crèche (institutional building, educational facility), an office floor converted to a dormitory (accommodation building), a hall converted to a dining hall for 50 or more people (assembly part). In all three, the existing building privilege ends. How the process is run is explained in the article on the fire design approval process.

Field note

In a mixed project, the ground floor was designed as commercial and the upper floors as offices, and the design report had written the two classes correctly and separately. The problem appeared in construction: a service shaft passing through the compartment floor separating the two parts had been left in the same volume as the shop storeroom on the commercial floor.

Two use classes that were separate on paper had become a single volume through the shaft. In this case Article 18 comes into play and the rules of the class requiring the higher protection measures apply to the whole building. The lesson: class separation is not a drawing decision but a continuity decision (BYKHY Article 24(7)). A class separation is only as valid as its weakest penetration.

Checklist

• Has the use class of each part been written exactly with the naming in Article 8(1)?
• Have educational and healthcare parts been defined under the "institutional building" heading (Article 11)?
• If there is a student dormitory, has it been classified as an accommodation building (Article 10)?
• Is there a part where 50 or more people gather? Has it been assessed as an assembly part (Article 15(1))?
• Are the storage parts inside the building below or above 50 m² (Article 16(2))?
• In mixed use, can the separation between parts be achieved with a fire separation suitable for the higher hazard class (Article 18)?
• If separation cannot be achieved, has the water and pump capacity been calculated according to the highest hazard class (Article 19(1))?
• Have the maximum compartment area from Annex 4 and the resistance periods from Annex 3/C been taken according to the use class?
• If there is doubt about the use class, has the Article 8(2) route been used in writing?
• In an existing structure, does the change of use fall within the Article 138(1) list?

FAQ

What are the building use classes in BYKHY?

Buildings are divided into ten classes according to their use: residential buildings, accommodation buildings, institutional buildings, office buildings, commercial buildings, industrial structures, assembly buildings, storage facilities, high hazard places and mixed-use buildings (BYKHY Article 8(1)). Educational facilities and healthcare buildings are not separate classes but sub-headings of institutional buildings (BYKHY Article 11).

Which class's rules apply in a mixed-use building?

If a building has parts subject to two or more use classifications, and these parts cannot be separated from each other by a fire separation suitable for the higher hazard class, or separate protection measures cannot be applied because they are intermingled, the rules of the classification requiring the higher protection measures apply to the whole building (BYKHY Article 18).

What happens if there is doubt about the use class?

Where any doubt arises concerning the use class of buildings, the assessment and decision of the Ministry of Environment, Urbanisation and Climate Change is followed (BYKHY Article 8(2)). In other words, the argument is closed by the Ministry's decision, not by the design team's interpretation; this route should be used in writing in the design.

Do small parts inside a building count as a separate class?

No. Parts used for office services within another building are subject to the classification of the main building (BYKHY Article 12(2)). Small commercial parts in a building that falls mainly in another use class are subject to the building's main classification (BYKHY Article 13(2)). Assembly parts suitable for fewer than 50 people (BYKHY Article 15(2)) and storage parts smaller than 50 m² inside a building (BYKHY Article 16(2)) are also subject to the classification of the main building.

References

• Turkish Regulation on Fire Protection of Buildings (BYKHY), Council of Ministers Decision No. 2007/12937 of 27/11/2007, Official Gazette 19.12.2007/26735 and amendments: OG 09/09/2009-27344; OG 05/04/2012-28255; OG 09/07/2015-29411; Council of Ministers Decision No. 2017/10459 of 14/06/2017 (in force 29/06/2017); Council of Ministers Decision No. 2018/11347 of 05/02/2018 (in force 15/03/2018); OG 04/11/2020-31294 (Presidential Decision 3167); OG 20/11/2021-31665 (Presidential Decision 4825); OG 01/07/2025-32943 (Presidential Decision 10026). Current text: mevzuat.gov.tr (consolidated text)
• Articles used in this article: Articles 8(1)-8(2) (use classes), Article 9 (residential), Article 10 (accommodation), Articles 11(1)(a) and 11(1)(b) (institutional buildings: education and healthcare), Articles 12(1)-12(2) (office), Articles 13(1)-13(2) (commercial), Article 14 (industrial), Articles 15(1)-15(2) (assembly, 50 people), Articles 16(1)-16(2) (storage, 50 m²), Article 17(1) (high hazard places), Article 18 (mixed use), Articles 19(1)-19(2)(a) (hazard classification, 126 m² and 30 minutes), Article 24(6) and Annex 4 (compartment areas), Article 24(7) (compartment continuity), Article 29(7) with Annex 3/B and Annex 3/C (resistance periods), Articles 32(1)-32(3) with Annex 5/A and Annex 5/B (occupant load, exit width, travel distance), Article 138(1) and Article 139 (change of use in an existing structure).
• TS EN 13501-1 Reaction-to-fire classification of construction products (the standard referenced in the Regulation through Annex 2/Ç).

All article numbers and values in this article are taken from the text of the Regulation published in the Official Gazette. Even so, the current text should be used for design, and the design should be carried out by an authorised engineer.

SprinkCalc — Fire Sprinkler Design Across Three Standards

SprinkCalc covers hazard classification, design density and area, K-factor selection, water demand and hydraulic calculations for NFPA 13, FM Global and BS EN 12845 in a single iOS app, and exports a professional PDF report.

Download SprinkCalc on the App Store

MEP Calc — 110+ Engineering Calculators

MEP Calc bundles 110+ engineering modules in one iOS app: 21 fire calculations plus heating, cooling, HVAC, plumbing, steam and natural gas.

Download MEP Calc on the App Store