Bygningsreglementets vejledning til kap 5 - Brand (Kapitel 3: Bærende konstruktioner) – Fire Safety Guidance for Load-Bearing Structures
This document serves as the official guidance for Kapitel 3: Bærende konstruktioner (Chapter 3: Load-bearing structures) within the framework of the Danish Building Regulations 2018 (BR18), specifically addressing Chapter 5 on Fire (Brand). Issued by the Danish Transport, Construction and Housing Authority (Trafik-, Bygge- og Boligstyrelsen), the guidance provides technical interpretations for compliance with the functional requirements of BR18 §§ 99-103. It establishes the regulatory baseline for ensuring that buildings maintain structural stability during fire incidents to facilitate safe evacuation and emergency rescue operations.
The scope of the guidance encompasses a wide range of structural elements, including columns, beams, walls, decks, stairs, balconies, and access galleries. It details the methodology for determining fire resistance performance using either standard fire exposure according to DS/EN 1363-1 or natural fire curves as specified in Eurocode 1 (DS/EN 1991-1-2). The document is structured to provide specific performance examples for buildings categorized within Risk Classes 1-3 (risikoklasse 1-3), utilizing fire resistance classes such as R 30, R 60, and R 120 based on building height and use category (anvendelseskategori).
Key technical areas addressed include the interaction between building sections of different heights, the fire safety of combined structural components, and specific material requirements for non-load-bearing facade elements and fixings. The guidance also integrates pre-accepted solutions found in the annexes to the building regulations, providing a standardized path for professional documentation of fire safety compliance.
Fire Resistance Requirements by Building Height and Use
Fire resistance for load-bearing components is determined based on the building height, measured from the terrain to the floor level of the top story, and the designated Use Category (anvendelseskategori). Minimum classes are defined to ensure that a collapse does not occur before evacuation and fire service interventions are complete.
- Buildings up to 12 meters: Generally require components of class R 30 [BD-bygningsdel 30] for Use Categories 1-5.
- Buildings between 12 and 45 meters: Typically require components of class R 60 [BD-bygningsdel 60] for the top story and R 120 [BS-bygningsdel 120] for lower floors.
- Basement structures: Floors over basements and their supporting structures require class R 60 / A2-s1,d0 for buildings up to 12m, and R 120 / A2-s1,d0 for buildings up to 45m.
Building Sections with Differing Heights
When a building consists of multiple sections with varying heights, the load-bearing structures in lower sections may sometimes be designed with lower fire resistance than the taller sections. This is permitted only if the sections are statically independent.
- Static Independence: If a collapse in the lower section does not affect the stability of the taller section, differing fire classes may be applied.
- Shared Systems: If the lower section's static system supports or influences the taller section, all shared components must meet the higher fire resistance requirements of the taller structure.
Combined Components and Fire Wall Replacements
The document specifies that joints between structural components must have fire resistance at least equal to the components they connect. Special rules apply to components supporting fire-separating elements.
- Fire Wall Replacements (brandkamserstatninger): Structures supporting a fire wall replacement must have fire resistance equal to the replacement itself, regardless of the general floor requirements in Table 1.
- Horizontal Supports: Floor structures supporting vertical load-bearing elements must match the fire resistance of those vertical elements to prevent premature failure.
- Fire Separation Support: If a load-bearing element supports a fire separation class EI 60, the load-bearing element itself must maintain at least class R 60.
Stairs, Balconies, and Facades
Specific requirements apply to elements utilized for evacuation and the external building envelope to prevent fire spread and hazard from falling parts.
- Stairs: Requirements vary from Material Class D-s2,d2 for low-rise buildings to R 30 / A2-s1,d0 for buildings up to 22 meters.
- Balcony Fixings: Mounting brackets for glass facades and non-load-bearing elements must be class A2-s1,d0 with a melting point above 850°C.
- Automatic Ventilation: In single-story buildings with automatic fire ventilation, load-bearing requirements may be waived if the fire section is under 1,000 m².
Frequently Asked Questions
What is the minimum fire resistance for a building under 12 meters in height?
For buildings in Use Categories 1-5 with a height up to 12 meters, the minimum requirement for load-bearing components is generally class R 30.
Are there specific material requirements for balcony fixings?
Yes, fixings for balconies and glazed facade elements must be made of class A2-s1,d0 materials with a melting point exceeding 850°C.
How is building height measured for fire classification?
Height is measured from the outdoor terrain level to the top surface of the floor in the highest story.
What are the requirements for structures supporting a fire wall replacement?
Supporting structures for a fire wall replacement (brandkamserstatning) must have a fire resistance period at least equal to the fire wall replacement itself.
When can load-bearing structures be designed without a fire resistance rating?
This is possible in single-story buildings with automatic fire ventilation if the fire section is no larger than 1,000 m², or for sections larger than 1,000 m² where specific load-bearing area limits are met.
What is required for stairs in buildings up to 22 meters high?
Escape route stairs in buildings up to 22 meters high must meet fire resistance class R 30 / A2-s1,d0.
