The Turkish Regulation on Fire Protection of Buildings (BYKHY) has two separate height definitions, and when they are confused the design drifts to the unsafe side. Building height is the distance from the point at which the building's datum level is taken up to eaves level (BYKHY Article 4(h)). Structure height is the total height of all floors, including basements, mezzanines and roof-space rooms (BYKHY Article 4(bbb)).
The numerical value of the high-rise threshold and the logic behind it are covered separately in the high-rise threshold article. Here the focus is not on the threshold itself but on how the threshold is measured and which provision uses which definition.
Two definitions, two different references
The definitions read as follows:
- Building height: the distance from the point at which the building's datum level is taken up to eaves level, or the height laid down in the zoning plan and in this Regulation (BYKHY Article 4(h)).
- Structure height: the total height of all constructed floors of the structure, including basements, mezzanines and roof-space rooms (BYKHY Article 4(bbb)).
- Basement floor: a floor built below the plinth level that lies partly below natural or graded ground (BYKHY Article 4(ı)).
The second part of the building height definition is often overlooked on site: the definition also covers the height laid down in the zoning plan and in the Regulation (BYKHY Article 4(h)).
A high-rise building is defined as a building whose building height exceeds 21.50 m and whose structure height exceeds 30.50 m (BYKHY Article 4(ccc)). Because both values appear in the same definition, both must be calculated and reported in the design. Saying "we are below the threshold" on the strength of a single number skips half of the definition.
Which provision uses which definition
| Provision | Criterion | Value |
|---|---|---|
| High-rise definition (Article 4(ccc)) | Building height and structure height | 21.50 m and 30.50 m |
| Compartment floor limit (Article 24(4)) | Building height | Non-residential above 21.50 m, residential above 30.50 m: at most three floors per compartment |
| External façade material class (Article 27(1)) | Building height | 28.50 m |
| Façade fire barrier (Article 27(2)(b)) | Building height | 6.50 m and 28.50 m |
| Escape stair pressurisation (Article 89(1)) | Height of the stair enclosure, residential excluded | 30.50 m |
| Pressurisation of stairs serving basements (Article 89(2)) | Number of basement floors | More than 4 |
| Pressurisation in residential buildings (Article 89(3)) | Structure height | 51.50 m |
| Fire lobby in front of the escape stair (Article 34(7)) and lift landing door resistance (Annex 3/B) | Structure height | 51.50 m |
The second row of the table needs attention. The compartment floor limit is written in terms of building height for residential buildings as well: in non-residential buildings with a building height over 21.50 m and in residential buildings with a building height over 30.50 m, the floors above those heights are arranged with at most three floors forming one fire compartment (BYKHY Article 24(4)). Checking this provision against structure height is a common mistake.
For pressurisation the criterion changes: in all buildings except residential ones, the escape stairs must be pressurised if the height of the stair enclosure exceeds 30.50 m (BYKHY Article 89(1)); the escape stairs of residential buildings with a structure height above 51.50 m must be pressurised (BYKHY Article 89(3)). The detail of these thresholds is given in the pressurisation thresholds article.
There is also a trigger independent of height: in buildings with more than 4 basement floors, the escape stairs serving the basement are pressurised (BYKHY Article 89(2)).
Why basements are treated separately
Basement floors are included in the structure height definition (BYKHY Article 4(bbb)), but the real difficulty with basements lies on the escape side. The Regulation sets separate provisions for basements: the floor between the basement and the ground floor is determined as REI 90 or the Annex 3/C value, whichever is greater (Annex 3/B, row 3-d); where a normal-floor stair continues down to the basement and serves more than 4 floors including basements, a fire lobby is provided for entry to the stair on the basement floors, except for special cases for residential buildings (BYKHY Article 46(2)(a)).
There is a difference on the door side too: escape stair and fire lobby doors must have at least 90 minutes of fire resistance if they serve basement floors, regardless of the number of floors (BYKHY Article 47(3)).
Mezzanines and roof-space rooms are also within the structure height definition (BYKHY Article 4(bbb)); a mezzanine added later changes both the structure height and the occupant load.
Floor area: the actual thresholds in the Regulation
The Regulation does not have a separate definition clause for "floor area", but it uses floor area directly as a threshold. The main places you will meet it in design practice are:
- Evacuation drawings for floors with a floor area over 2,000 m² are prepared separately from the architectural drawings (BYKHY Article 6(4)).
- Escape routes are determined on the basis of the occupancy class, occupant load and floor area (BYKHY Article 31(3)).
- Except for residential buildings, manual call points are mandatory in all buildings of two to four floors with a floor area over 400 m² (BYKHY Article 75(2)(a)).
- In high-rise buildings, and in shopping centres, car parks and similar premises with a floor area over 1,000 m², fire brigade water outlet connections are provided (BYKHY Article 94(1)(a)(1)).
Alongside these there are two more area concepts, and they cannot be used interchangeably. Compartment area is given in Annex 4 by occupancy class (BYKHY Article 24(6)); the detail is tabulated in the fire compartment areas article.
The area used for the occupant load calculation. The values in Annex 5/A are used as occupant load factors (BYKHY Article 32(1)). The note to Annex 5/A is critical: the occupant load is calculated on the net area for the uses in rows 1, 2, 3 and 4 of the table, and on the gross area for the uses in the other rows. In rooms where the number of people is fixed, the stated number of people is used, provided it is not less than the calculated value.
This note means that two different area definitions are used side by side in the same building. If the report does not state which rows use net area and which use gross area, the occupant load is recalculated at review and comes out differently.
There is an area threshold on the hazard class side too: 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)).
Stating the measurement reference
The Regulation defines building height from the point at which the datum level is taken (BYKHY Article 4(h)), but on sloping ground the value cannot be checked unless the design shows where that point is. The way to handle it in practice:
The datum point should be marked on the architectural drawings; building height and structure height should each be stated with their measurement reference; any height laid down in the zoning plan should be included in the report as required by Article 4(h); and for designs close to a threshold, a construction tolerance scenario should be discussed from the start.
The discipline of putting the measurement reference in writing applies not only to height but also to escape: the most remote point from which travel distance is measured is taken 40 cm in front of the walls enclosing the room (BYKHY Article 32(6)). The logic of this rule is explained in the travel distance 40 cm rule article.
What changes once a building is high-rise
Once a building falls within the definition, not a single provision but a whole set of provisions comes into play:
- Internal wall linings and internal thermal and acoustic insulation in high-rise buildings are made of at least low-flammability material (BYKHY Article 29(3)).
- In high-rise buildings, the walls of vertical service shafts and chutes such as refuse, communications, document and technical equipment shafts must have at least 120 minutes of fire resistance, and their access hatches at least 90 minutes, and be smoke-tight (BYKHY Article 25(3)).
- In high-rise buildings and in terraced (adjoining) construction, the floors on which roofs sit act as horizontal fire barriers, and the roof structure and coverings are made of non-combustible material (BYKHY Article 28(3)).
- Manual call points are mandatory in all high-rise buildings, including residential ones (BYKHY Article 75(2)(c)), and floor finishes are made of at least low-flammability material (BYKHY Article 26(2)).
An overall view of high-rise requirements on the systems side is given in the fire requirements for high-rise buildings article. For the specific risks of the car park use that tends to be concentrated in basements, see the car park fire protection article.
Field note
For an office building on sloping ground, the design kept the building height below the threshold by measuring it from the low façade. Because the ground fell away at the rear façade, the same building was above the threshold when viewed from the other side. The difference was spotted at approval stage, and the pressurisation requirement under Article 89(1) came up in the middle of the project.
The habit that follows from this: report the height not as a single number but as the number plus the measurement point plus a check of the most unfavourable façade. Moreover, Article 4(ccc) names both values together; a high-rise assessment is not complete until building height and structure height have each been stated.
Checklist
- Have building height (Article 4(h)) and structure height (Article 4(bbb)) each been calculated and reported?
- Is the datum point marked on the drawings, and has the zoning plan height been included in the report?
- Has the high-rise assessment been made on both values in Article 4(ccc) together?
- Has the compartment floor limit been checked against building height, as Article 24(4) requires?
- Has the pressurisation check been made separately for Articles 89(1), 89(2) and 89(3)?
- Have the floor area thresholds been checked: 400 m² (Article 75(2)(a)), 1,000 m² (Article 94(1)(a)(1)), 2,000 m² (Article 6(4))?
- Has the net/gross area distinction of Annex 5/A been applied in the occupant load calculation and stated in the report?
FAQ
What is the difference between building height and structure height in BYKHY?
Building height means the distance from the point at which the building's datum level is taken up to eaves level, or the height laid down in the zoning plan and in the Regulation (BYKHY Article 4(h)). Structure height is the total height of all constructed floors of the structure, including basements, mezzanines and roof-space rooms (BYKHY Article 4(bbb)). In the same building the two definitions give different numbers.
How does BYKHY define a high-rise building?
A high-rise building is a building whose building height exceeds 21.50 m and whose structure height exceeds 30.50 m (BYKHY Article 4(ccc)). Once a building falls within this definition, many provisions become stricter at the same time, including internal lining and insulation materials, vertical shaft walls, compartment layout and firefighting infrastructure.
Which height value do basement floors count towards?
A basement floor is a floor built below the plinth level that lies partly below natural or graded ground (BYKHY Article 4(ı)). Basement floors are expressly included in the structure height definition (BYKHY Article 4(bbb)). In addition, in buildings with more than 4 basement floors, the escape stairs serving the basement are pressurised regardless of height (BYKHY Article 89(2)).
At which thresholds does floor area appear in BYKHY?
Evacuation drawings for floors with a floor area over 2,000 m² are prepared separately from the architectural drawings (BYKHY Article 6(4)). Except for residential buildings, manual call points are mandatory in buildings of two to four floors with a floor area over 400 m² (BYKHY Article 75(2)(a)). In high-rise buildings, and in shopping centres, car parks and similar premises with a floor area over 1,000 m², fire brigade water outlet connections are provided (BYKHY Article 94(1)(a)(1)).
References
- Turkish Regulation on Fire Protection of Buildings (BYKHY), Council of Ministers Decision 2007/12937 of 27/11/2007, Official Gazette 19/12/2007, No. 26735. Amendments: OG 09/09/2009-27344; OG 05/04/2012-28255; OG 09/07/2015-29411; Council of Ministers Decision 2017/10459 of 14/06/2017 (in force 29/06/2017); Decision 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: Article 4(h) (building height), 4(ı) (basement floor), 4(bbb) (structure height), 4(ccc) (high-rise building), Article 6(4) (floor area 2,000 m²), Article 19(2)(a) (126 m²), Article 24(4) (compartment floor limit), Article 24(6) and Annex 4 (compartment area), Article 25(3) (shaft walls in high-rise buildings), Article 26(2) (floor finishes), Articles 27(1) and 27(2)(b) (façade), Article 28(3) (roof), Articles 29(3) and 29(4) (materials in high-rise buildings), Article 29(7) with Annexes 3/B and 3/C, Article 31(3) (determining escape routes), Article 32(1) and Annex 5/A (occupant load, net and gross area), Article 32(6) (40 cm), Article 34(7) (fire lobby), Article 46(2)(a) (basement escape stair), Article 47(3) (door fire resistance), Articles 75(2)(a) and 75(2)(c) (manual call points), Articles 89(1), 89(2), 89(3) (pressurisation), Article 94(1)(a)(1) (fire brigade water outlet line).
- 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 Regulation text published in the Official Gazette. Even so, the current text must govern in design, and design must be carried out by an authorised engineer.
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Download MEP Calc on the App StoreSources are listed in the References section at the end of the article. Quotations from the regulation are unofficial English translations of the Turkish text. This article is for general information; for article numbers, thresholds and exemptions, the current regulation and standard texts published in the Official Gazette govern, and design must be carried out by an authorised engineer.