Types of Buildings

The BNBC 2020, published on February 11, 2021, categorizes buildings based on occupancy and construction type to ensure appropriate standards for safety, structural integrity, and functionality. These classifications are primarily outlined in Part 3: General Building Requirements, Control, and Regulation of the Code, with additional details in Part 4: Fire Protection and Part 6: Structural Design. Below is a detailed breakdown of the building types based on occupancy and construction and their specific requirements.

1. Classification of Buildings Based on Occupancy

The BNBC 2020 classifies buildings into various occupancy categories based on their primary use or function. Each category is assigned a letter (e.g., A, B, C) and subdivided into specific types to address the unique requirements of different activities. The following are the major occupancy classifications:

A: Residential Buildings

Residential buildings are designed for dwelling purposes, accommodating individuals or families for living, sleeping, and daily activities. This category is subdivided into:

• A1: Single-Family Detached Houses
• One family occupies standalone houses, typically with private entrances and independent facilities.
  • Key Requirements: Minimum setbacks, adequate ventilation, and natural lighting per BNBC standards. Fire safety measures include smoke detectors and escape routes.
  • Example: Bungalows, cottages, or standalone villas.
• A2: Two-Family Dwellings (Duplexes)
• Buildings housing two separate families, often with shared walls or floors but independent entrances.
  • Key Requirements: Sound insulation between units, fire separation walls, and compliance with floor area ratio (FAR) regulations.
  • Example: Duplex homes.
• A3: Flats or Apartments
• Multi-unit residential buildings with shared common areas like staircases, elevators, or corridors.
  • Key Requirements: Structural stability for multi-story designs, fire-resistant materials, and mandatory provisions for lifts in buildings over a certain height (typically above six stories).
  • Example: High-rise apartment complexes.
• A4: Mess, Boarding Houses, or Dormitories
• Buildings providing group accommodation with shared facilities for temporary or long-term residents.
  • Key Requirements: Enhanced fire safety systems, including sprinklers and alarms, due to higher occupant density. Adequate sanitation and ventilation are critical.
  • Example: Student dormitories, worker hostels.
• A5: Hotels and Lodging Houses
• Commercial residential buildings offering temporary accommodation, such as hotels, motels, or guest houses.
  • Key Requirements: Compliance with FAR and maximum ground coverage (MGC) based on plot size and road width (e.g., FAR of 6.0 for plots above 20 Katha with an 18-meter road). Fire evacuation plans and accessibility features are mandatory.
  • Example: Five-star hotels, budget inns.

B: Educational Buildings

These buildings are used for educational purposes, including teaching, training, or research.

• B1: Schools and Colleges
• Facilities for primary, secondary, or higher secondary education.
  • Key Requirements: Spacious classrooms, emergency exits, and fire-resistant construction materials. Accessibility for differently-abled individuals is emphasized.
  • Example: Public schools and private colleges.
• B2: Universities and Research Institutions
• Buildings for higher education or specialized research.
  • Key Requirements: Advanced structural design to accommodate laboratories, auditoriums, and libraries. Seismic resilience is critical in high-risk zones.
  • Example: University campuses research centers.

C: Institutional Buildings

Institutional buildings serve public or semi-public purposes, often involving care or confinement.

• C1: Hospitals and Clinics
• Facilities providing medical treatment or care.
  • Key Requirements: Strict hygiene standards, fire detection and extinguishing systems, and seismic-resistant designs due to critical operations.
  • Examples: General hospitals and specialized clinics.
• C2: Custodial Institutions
• Buildings for individuals under custody, such as jails or juvenile detention centers.
  • Key Requirements: High-security features, fire-resistant materials, and controlled access points.
  • Examples: Prisons reformatories.
• C3: Community Centers
• Facilities for community gatherings or social activities.
  • Key Requirements: Flexible interior spaces, adequate parking, and compliance with fire safety norms.
  • Examples: Town halls and cultural centers.

D: Assembly Buildings

These are buildings where groups gather for social, recreational, or religious purposes.

• D1: Large Assembly Halls
• Facilities accommodating large crowds, such as theaters or convention centers.
  • Key Requirements: Multiple egress points, fire sprinklers, and robust structural systems to handle dynamic loads.
  • Examples: Auditoriums and concert halls.
• D2: Smaller Assembly Spaces
• Smaller venues for gatherings, such as community halls or religious buildings.
  • Key Requirements: Adequate ventilation, fire alarms, and compliance with occupancy load limits.
  • Examples: Mosques, churches, and local meeting halls.

E: Business Buildings

Business buildings are used for commercial or professional activities.

• E1: Offices
• Buildings for administrative or professional work.
  • Key Requirements: Energy-efficient designs, fire-resistant partitions, and provisions for HVAC systems.
  • Examples: Corporate offices and government buildings.
• E2: Retail and Mercantile
• Facilities for selling goods or services.
  • Key Requirements: Display areas, fire safety systems, and customer accessibility.
  • Examples: Shopping malls and department stores.
• E3: Professional Service Buildings
• Buildings for specialized services, such as banks or consultancies.
  • Key Requirements: Security features, fire safety compliance, and ergonomic design.
  • Example: Law firms and financial institutions.

F: Mercantile Buildings

These are dedicated to the display and sale of goods.

• F1: Large Retail
• Large-scale retail outlets with high customer traffic.
  • Key Requirements: Wide circulation spaces, fire suppression systems, and parking facilities.
  • Examples: Supermarkets and hypermarkets.
• F2: Small Shops
• Smaller retail units, often in mixed-use developments.
  • Key Requirements: Fire separation from adjacent units, adequate lighting, and ventilation.
  • Example: Local grocery stores and boutiques.

G: Industrial Buildings

Industrial buildings are used for manufacturing, processing, or storage.

• G1: Low-Hazard Industries
• Facilities with minimal risk, such as food processing or textile manufacturing.
  • Key Requirements: Ventilation systems, fire-resistant materials, and compliance with environmental regulations.
  • Examples: Garment factories and food packaging plants.
• G2: Moderate-Hazard Industries
• Industries with moderate risks, such as chemical processing.
  • Key Requirements: Specialized fire suppression systems, spill containment, and worker safety measures.
  • Examples: Pharmaceutical plants paint factories.
• G3: High-Hazard Industries
• Facilities handling highly flammable or hazardous materials.
  • Key Requirements: Explosion-proof designs, advanced fire protection systems, and strict zoning compliance.
  • Examples: Oil refineries and ammunition factories.

H: Storage Buildings

Storage buildings are designed for warehousing or storing goods.

• H1: General Storage
• Warehouses for non-hazardous materials.
  • Key Requirements: High load-bearing floors, fire-resistant walls, and efficient stacking systems.
  • Example: Logistics warehouses, grain silos.
• H2: Hazardous Storage
• Facilities storing flammable or toxic materials.
  • Key Requirements: Explosion vents, chemical-resistant materials, and compliance with safety standards.
  • Examples: Fuel depots and chemical storage units.

I: Hazardous Buildings

These buildings handle hazardous materials or processes.

• I1: Explosive Materials
• Facilities dealing with explosives or highly reactive substances.
  • Key Requirements: Remote location, blast-resistant construction, and stringent fire safety measures.
  • Example: Fireworks manufacturing units.
• I2: Toxic or Radioactive Materials
• Buildings for storing or processing toxic or radioactive substances.
  • Key Requirements: Containment systems, radiation shielding, and emergency response plans.
  • Example: Nuclear waste storage facilities.

J: Miscellaneous Buildings

This category includes buildings that do not fit into other classifications, such as parking garages, utility structures, or temporary shelters.

• Key Requirements: Vary based on specific use, including basic fire safety and structural stability.
• Example: Car parks, temporary event tents.

2. Classification of Buildings Based on Construction Type

In addition to occupancy, the BNBC 2020 classifies buildings based on their construction type, primarily focusing on fire resistance and structural materials. This classification is detailed in Part 3, Chapter 3, and is crucial for determining fire safety requirements and structural design standards. The construction types are:

Type I: Fire-Resistive Construction

• Description: Buildings constructed with non-combustible materials, such as reinforced concrete or protected steel, offer the highest fire resistance (typically 3-4 hours).
• Applications: High-rise buildings, hospitals, and large assembly buildings (e.g., Occupancy A3, C1, D1).
• Key Requirements: Fire-resistant walls, floors, and roofs; advanced fire suppression systems; and seismic-resistant designs.
• Examples: Multi-story office towers and major hospitals.

Type II: Non-Combustible Construction

• Description: Similar to Type I, but slightly lower fire resistance (1-2 hours). It uses non-combustible materials but with less stringent fireproofing.
• Applications: Medium-rise commercial or industrial buildings (e.g., Occupancy E1, G1).
• Key Requirements: Fire-resistant structural elements and compliance with load-bearing standards.
• Examples: Warehouses and mid-rise office buildings.

Type III: Ordinary Construction

• Description: Buildings with exterior walls of non-combustible materials (e.g., masonry) but interior elements (e.g., wooden floors or roofs) that may be combustible. Fire resistance is moderate (1-2 hours).
• Applications: Small commercial or residential buildings (e.g., Occupancy A1, F2).
• Key Requirements: Fire separation between units and limited use of combustible materials.
• Examples: Small shops low-rise apartments.

Type IV: Heavy Timber Construction

• Description: Buildings using large-dimension timber for structural elements provide good fire resistance due to the slow-burning nature of heavy wood.
• Applications: Traditional or aesthetic buildings, such as cultural or religious structures (e.g., Occupancy D2).
• Key Requirements: Minimum timber dimensions per BNBC, fire-resistant coatings, and adequate ventilation.
• Examples are heritage buildings and large wooden mosques.

Type V: Wood-Frame Construction

• Description: Buildings primarily constructed with combustible materials, such as wood, offering the lowest fire resistance (less than 1 hour).
• Applications: Low-rise residential buildings or temporary structures (e.g., Occupancy A1, J).
• Key Requirements: Fire-retardant treatments, smoke detectors, and strict height limitations.
• Example: Single-family wooden houses, temporary shelters.

3. Key Design and Regulatory Considerations

The BNBC 2020 imposes specific requirements for each building type to ensure safety, sustainability, and compliance. Some key considerations include:

• Floor Area Ratio (FAR) and Maximum Ground Coverage (MGC) regulate the building’s footprint and height based on plot size and road width. For example, residential buildings (A1-A4) on plots above 20 katha with a 12-meter road can have a FAR of 5.50 and an MGC of 50%.
• Setbacks: Minimum setbacks (e.g., 4.5 meters from roads) ensure open space, light, and ventilation. Basements can extend into mandatory open spaces up to 50% under specific conditions.
• Fire Safety: Fire detection, extinguishing systems, and egress routes are mandatory, with stricter requirements for high-occupancy or hazardous buildings (e.g., Occupancy D, I).
• Seismic Design: Bangladesh is divided into four seismic zones, with Zone 3 being the most active. Buildings in high-risk zones require enhanced seismic-resistant designs, particularly for Occupancy B and C.
• Energy Efficiency: Part 3, Chapter 4 emphasizes energy-efficient designs, including insulation, natural lighting, and renewable energy integration for sustainable construction.

4. Practical Implications for Engineers and Architects

The BNBC 2020 closely resembles ASCE 7-05 and incorporates updated provisions for earthquake and wind loads compared to BNBC 2006. Structural engineers, architects, and planners must refer to the code for:

• Design Loads: Part 6, Chapter 2 specifies loads (e.g., dead, live, wind, seismic) for different building types.
• Material Standards: Part 5 details approved building materials, including concrete, steel, timber, and bamboo.
• Construction Practices: Part 7 outlines safety protocols during construction, such as scaffolding and demolition procedures.

Conclusion

The BNBC 2020 provides a robust framework for classifying buildings based on occupancy and construction type, ensuring that each structure meets stringent safety, structural, and sustainability standards. By categorizing buildings into detailed occupancy groups (A to J) and construction types (I to V), the code addresses the diverse needs of Bangladesh’s residential, commercial, industrial, and institutional facilities. Engineers, architects, and builders must adhere to these classifications and associated requirements to create safe, efficient, and sustainable buildings, contributing to a resilient built environment in a seismically active and rapidly urbanizing country.