Code of practice for fire safety of buildings (general): Exposure hazard

IS 1643 - Scope: Key Formulas, Tables & Specifications

1. Scope Summary

IS 1643 governs floor area ratios (FAR), open spaces, and construction types for various occupancies, ensuring safety and urban planning compliance.

2. Floor Area Ratios (FAR) - Table 1 (Clause 4.1)

• UL = Unlimited
• NP = Not Permitted
• *Storage and Hazardous occupancies may have 20% FAR increase for accessory services (basements, utility rooms, etc.) per Note 4.

3. Open Spaces (Clause 5.3.1.1) - Front Open Space Requirements

IS 1643 - Exposure Hazard & Fire Spread: Key Points

1. Definition

• Exposure Hazard: Risk of fire spreading through open air from one building to another nearby building.

2. Key Factors (Clause 2.1)

• Building construction type and spacing.
• Classification per IS 1641-1988.
• Floor Area Ratio (FAR) and open space norms influence fire spread risk.

3. Spacing Requirements (General Guidance)

• Minimum distance between buildings depends on:
  • Building height.
  • Construction material.
  • Use and occupancy.
• Larger spacing reduces exposure hazard.

4. Important Specifications

• Use IS 1641 for building classification.
• Follow floor area ratio and open space guidelines from international norms (USA, UK, Canada) as referenced.
• Round off values per IS 2:1960 rules.

5. Typical Formula for Minimum Spacing (Indicative)

[ d_{min} = k \times H ] Where:

• ( d_{min} ) = minimum distance between buildings (m)
• ( H ) = height of the taller building (m)
• ( k ) = factor based on construction type and fire hazard class (usually 0.5 to 1.5)

Summary Table (Indicative)

flowchart LR
    A[Building on Fire] --> B[Exposure Hazard]
    B --> C[Fire Spread Risk]
    C --> D[Spacing & Construction]
    D --> E[Fire Safety Measures]

Note: For exact values, refer to IS 1643 tables and IS 1641 classifications. This summary covers principles; always consult the full code for design.

IS 1643: Maximum Height of Buildings - Key Points & Tables

1. Definition of Maximum Height (Clause 3.1 & 4.2)

• Height and storeys depend on occupancy, type of construction (refer IS 1642), and street width or floor area ratio (FAR).
• Buildings separated by fire-resisting walls (≥ 4 hrs fire resistance) extending from foundation to 1m above roof can be treated as separate for height and floor area calculations.
• Openings in fire walls must have 4 hrs fire assemblies protection.

2. Open Space Requirements (Clause 5.3.3.1 & Table 2)

• Note 1: For buildings > 24 m, minimum front open space = 6 m.
• Note 2: If rooms don't get light/ventilation from exterior space, side/rear open space may reduce by 1 m (min 3 m, max 8 m), no projections allowed.

3. Summary

• Maximum height depends on:
  • Occupancy & construction type (IS 1642)
  • Fire separation walls (≥4 hrs)
  • Street width or FAR (see Clause 4)
  • Open spaces around building increase with height (see Table 2)

Diagram: Fire Separation Wall Concept

graph TD
    A[Building Portion 1] ---|4 hr fire wall| B[Building Portion 2]
    B ---|4 hr fire wall| C[Building Portion 3]
    style A fill:#f9f,stroke:#333,stroke-width:2px
    style B fill:#bbf,stroke

IS 1643 - Floor Area Ratio (FAR) Key Points

1. Definition:

• FAR = Total built-up floor area / Plot area.
• Controls building density related to occupancy and construction type.

2. FAR Values (Table 1) for buildings facing a public street ≥ 9 m wide:

• UL = Unlimited
• NP = Not permitted

3. Notes:

• FAR may be increased by 20% for accessory spaces like basements, parking, utility rooms, staircases, architectural features, etc.
• Separate building portions divided by 4-hour fire-resisting walls can be considered independently for FAR.
• Overall building height and open space requirements depend on street width and occupancy (see Clause 3.1).

4. Practical Use:

[ \text{Maximum Permissible Floor Area} = \text{Plot Area} \times \text{FAR (from Table 1)} ]

flowchart TD
    A[Plot Area] --> B[Determine Occupancy & Construction Type]
   

IS 1643 - Open Spaces Key Specifications

1. Exterior Open Space (Clause 5.3.1)

• Open spaces around buildings ensure light, ventilation, and fire safety.

2. Rear Open Space (Clause 5.3.1.2)

• Minimum rear open space depends on building height.

3. Side and Rear Open Spaces for Buildings >10 m (Clause 5.3.3.1, Table 2)

• Note 1: For buildings >24 m, minimum front open space = 6 m.
• Note 2: If rooms don't get light/ventilation from exterior open space, open space width can be reduced by 1 m, limited between 3 m and 8 m. No projections allowed.

4. Floor Area Ratio (FAR) & Construction Types (Clause 4.1, Table 1)

IS 1643 - General Requirements for Open Spaces

1. Exterior Open Space (Clause 5.3.1)

• Minimum front open space depends on street width:

• Minimum front open space for buildings above 24 m height: 6 m

2. Side and Rear Open Spaces (Clause 5.3.3.1, Table 2)

• Note: If rooms do not get light/ventilation from the exterior, open space can reduce by 1 m (min 3 m, max 8 m).

3. Floor Area Ratio (FAR) (Clause 4.1, Table 1)

IS 1643: Open Spaces Separate for Each Building or Wing

Key Points from Clauses 5.2, 5.3.3.1, 5.3.5

1. Separate Open Spaces (Clause 5.2)

• Each building or wing must have distinct open spaces for lighting and ventilation.
• For buildings with multiple wings, each wing requires its own open space.

2. Side and Rear Open Spaces (Clause 5.3.3.1 & Table 2)

• Note 1: Buildings above 24 m require a minimum front open space of 6 m.
• Note 2: If rooms don’t get light/ventilation from exterior open space, width can be reduced by 1 m (min 3 m, max 8 m).

3. Interior Open Spaces (Clause 5.3.5)

a) Inner Courtyard

• Minimum width: 3 m
• Minimum area:
  [ \text{Area} \geq \left(\frac{1}{5} \times \text{height of highest wall}\right)^2 ]

b) Ventilation Shaft for Bathrooms/WCs

IS 1643 Key Specifications for Residential Buildings

1. Floor Area Ratio (FAR) - Clause 4.1, Table 1

• UL = Unlimited FAR subject to height restrictions.
• FAR can be increased by 20% for accessory structures like basements, utility rooms, stair/lift rooms, etc.

2. Open Space Requirements - Clause 5.3.3.1, Table 2

• Front open space ≥ 6 m for buildings > 24 m height.
• Open space width can be reduced by 1 m (min 3 m, max 8 m) if rooms do not get light/ventilation from exterior.

Summary:

• FAR depends on construction type; max 2.0 for Type 1.
• Open spaces increase with building height to ensure ventilation and fire safety.
• Accessory structures can increase FAR by 20%.

flowchart TD
    A[Residential Building] --> B[FAR as per Type of Construction]
    B --> C[Type 1: 2.0 UL]
    B --> D[Type 2: 1.4]
    B --> E[Type 3: 1.0]
    A --> F[Open Space Requirements]
    F --> G{Building Height}
    G -->|≤10m| H

IS 1643 - Other Occupancies: Key Specifications & Tables

1. Floor Area Ratio (FAR) for Other Occupancies (Clause 4.1, Table 1)

• UL: Unlimited FAR
• NP: Not Permitted

2. Notes on FAR (Clause 4.1 Notes)

• Note 1: FAR values are subject to building height restrictions (see Table 2).
• Note 3: Local authorities may adjust FAR based on:
  • Dwelling density
  • Traffic & parking
  • Firefighting facilities
  • Water, drainage, sanitation
• Note 4: FAR may increase by 20% for:
  • Basements, parking under stilts, AC plant rooms
  • Utility structures (pumphouse, watchman booth, etc.)
  • Projections, accessory buildings
  • Stair/lift rooms above top storey, chimneys, tanks

3. Open Spaces (Clause 5.4.1)

• Hazardous

IS 1643: Exemptions to Open Spaces (Clause 5.5)

Key Points:

• Open spaces (front, side, rear) are mandatory for ventilation, light, and fire safety.
• Clause 5.5 provides exemptions where certain projections or accessory structures are allowed within open space, not counted as obstruction.
• Typical exemptions include:
  • Basements, cellars, parking under stilts.
  • Watchman’s booth, pumphouse, garbage shaft, electric cabin/substation.
  • Staircase rooms, lift rooms above top storey.
  • Architectural features, chimneys, elevated tanks within permissible dimensions.

Relevant Tables & Specifications

Table 2 (Clause 5.3.3.1): Side and Rear Open Spaces

Floor Area Ratio (FAR) Exemptions (Clause 4.1 Notes)

• FAR may be increased by 20% for exempted structures like basements, accessory buildings, and certain projections.
• Exemptions do not reduce minimum open space requirements but allow certain uses within open spaces.

Summary Diagram

flowchart TD
    A[Building] --> B(Open Spaces)
    B --> C{Height ≤ 10m}
    B --> D{Height > 10m}
    C --> E[Side/Rear Open Space = 3m]
    D --> F[Side/Rear Open Space from Table 2]
    F --> G[Exemptions Allowed]
    G --> H

IS 1643 - Limitations to Open Space

Key Clauses Summary:

• Clause 5.3.1: Exterior Open Space
  Specifies minimum open space around buildings for ventilation, lighting, and safety.

• Clause 5.3.1.2: Rear Open Space
  Defines minimum rear open space requirements based on building height and occupancy.

• Clause 5.5: Exemption to Open Spaces
  Lists cases where open space requirements can be relaxed, e.g., for certain industrial buildings or in congested areas.

• Clause 5.6: Limitations to Open Space
  Details maximum permissible encroachments or reductions in open space due to site constraints or functional necessities.

Typical Specifications (per IS 1643):

• Open space should be free from permanent structures except permitted projections (eaves, balconies).
• Exemptions apply only with proper justification and local authority approval.

Formula for Minimum Open Space (simplified):

[ \text{Minimum Open Space} \geq k \times \text{Building Height} ]

Where ( k ) varies between 0.25 to 0.5 depending on occupancy and fire risk.

flowchart TD
    A[Building Height] --> B{Height Range}
    B -->|Up to 9m| C[Rear Open Space = 3m]
    B -->|9-15m| D[Rear Open Space = 4.5m]
    B -->|Above 15m| E[Rear Open Space = 6m]
    F[Exemptions] --> G[Local Authority Approval]
    H[Limitations] --> I[Encroachments Allowed?]
    I -->|Yes| J[Within Specified Limits]
    I -->|No| K[Increase Open Space]

Note: Refer to IS 1643 Clause 5 for detailed tables and conditions. Always check local amendments.

IS 1643 - High Rise Buildings: Key Points & Specifications

1. Maximum Height & Fire Separation (Clause 4.2)

• Separate building portions divided by continuous fire-resisting walls (≥4 hours rating) from foundation to 1m above roof are treated as separate buildings for height and floor area calculations.
• Openings in separating walls must have 4-hour fire assemblies.

2. Mixed Occupancy (Clause 6.2)

• For buildings with multiple occupancies, design as per the most hazardous occupancy.
• If separated by a 4-hour fire-rated wall, occupancies can be treated individually.

3. Additions/Extensions (Clause 5.6.2)

• Allowed only if open spaces comply with Clause 5.3 after the addition.

Typical Fire Separation Requirements for High Rise Buildings:

Important Considerations:

• Refer IS 1642 for type of construction based on occupancy and exposure.
• Open spaces and floor area ratios must comply with relevant clauses (5.3, Table 1).
• Fire safety design must consider building height, occupancy hazard, and separation.

flowchart LR
    A[Building Portion 1] -- Fire Wall (4h) --> B[Building Portion 2]
    A & B --> Separate Height & Floor Area Calculations
    C[Mixed Occupancy] -->|No Fire Wall| D[Design as Most Hazardous]
    C -->|4h Fire Wall| E[Treat Individually]

For detailed fire safety design, always cross-check with IS 1642 and IS 1643 clauses on construction type and fire grading.

IS 1643: Means of Access for High Rise Buildings

Key Provisions (Clause 6.1)

• Minimum width of main street: ≥ 12 m.
• Street connectivity: One end must connect to another street ≥ 12 m wide.
• No dead ends: Roads should be continuous, not dead ends.
• Open spaces: Must not be used for parking; reserved for emergency access.
• Fire-fighting vehicle access: Adequate passageways and clearances must be provided for fire trucks.

Mixed Occupancy (Clause 6.2)

• For buildings with mixed occupancies, comply with the most hazardous occupancy requirements.
• If separated by a 4-hour fire-rated wall, treat occupancies individually.

Summary Table for Access (from Clause 6.1 & 6.2)

Fire Vehicle Access Clearance (General Practice)

• Minimum width of access road: 3.5 to 6 m (depending on vehicle size)
• Vertical clearance: ≥ 4.5 m
• Turning radius: Minimum 12 m outside radius for fire engines

flowchart LR
    A[Main Street ≥ 12m] --> B[Connected to Another Street ≥ 12m]
    B --> C[No Dead Ends]
    C --> D[Open Spaces Reserved - No Parking]
    D --> E[Fire Fighting Vehicle Access]
    E --> F{Mixed Occupancy?}
    F -- Yes --> G[Follow Most Hazardous Occupancy]
    F -- Separated by 4h Wall --> H[Treat Occupancies Individually]

Note: Always cross-check with local fire safety and municipal regulations for additional access requirements.

IS 1643: Mixed Occupancy Buildings - Key Points & Specifications

Clause 6.2: Mixed Occupancy

• When a building has multiple occupancy types, it must comply with the requirements for the most hazardous occupancy.
• If occupancies are separated by a fire-rated wall with 4-hour fire resistance, they can be treated as individual occupancies.

Important Tables and Guidelines

• UL = Unlimited; NP = Not Permitted.
• FAR values can be increased by 20% for accessory spaces like basements, pumphouses, stair rooms, etc.

Summary Formula for Mixed Occupancy Design:

[ \text{Design Criteria} = \max(\text{Criteria of each occupancy type}) ]

• Use the most stringent fire, structural, and safety requirements.
• Separate occupancies with a 4-hour fire-rated wall to treat independently.

flowchart TD
    A[Building with Mixed Occupancy] --> B{Is there a