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IS 16475:2016 is the Indian Standard (BIS) for flood resistant construction - guidelines for engineered buildings. This standard provides guidelines for planning, designing, and constructing engineered buildings in flood-prone areas to mitigate flood damage. It details methods for determining flood loads like hydrostatic, hydrodynamic, and debris impact forces, and provides design strategies such as 'dry proofing' and 'wet proofing' and foundation considerations.
Provides guidelines for flood resistant construction practices for engineered buildings.
Overview
Status
Current
Usage level
Specialized
Domain
Structural Engineering — Disaster Resilience and Retrofitting
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! Accurately determining the Design Flood Level (DFL) is the most critical first step; all other design parameters depend on it.
! Choose between 'wet proofing' (allowing water in and using durable materials below DFL) and 'dry proofing' (making the structure watertight). Dry proofing is only suitable for low flood depths and velocities.
! Do not neglect foundation design for scour. Floodwaters can erode soil from around footings, leading to catastrophic failure even if the building itself resists water pressure.
ASCE/SEI 24-14American Society of Civil Engineers (ASCE), USA
HighCurrent
Flood Resistant Design and Construction
Provides minimum requirements for design and construction of structures located in flood hazard areas.
BS 85500:2015British Standards Institution (BSI), UK
HighCurrent
Flood resilient construction. Improvement, resistance and resilience. Code of practice
Provides recommendations and guidance on flood resilience and resistance for new and existing buildings.
FEMA P-55Federal Emergency Management Agency (FEMA), USA
MediumCurrent
Coastal Construction Manual: Principles and Practices of Planning, Siting, Designing, Constructing, and Maintaining Residential Buildings in Coastal Areas
Focuses on residential buildings in coastal flood zones, including guidance on wind and wave loads.
Handbook for Construction in Flood Hazard AreasAustralian Building Codes Board (ABCB), Australia
HighCurrent
Construction of Buildings in Flood Hazard Areas
Provides non-mandatory guidance for the design and construction of buildings in flood-prone areas.
Key Differences
≠IS 16475 is a 'Guideline', providing recommendations, whereas ASCE 24 is a 'Standard' that is often adopted into law and becomes a mandatory requirement for construction in designated flood hazard areas in the US.
≠US standards like ASCE 24 and FEMA P-55 make a sharp, codified distinction between 'A-Zones' (riverine flooding) and 'V-Zones' (coastal flooding with wave action), with drastically different and stricter rules for V-Zones (e.g., mandatory open-pile foundations). IS 16475 addresses wave loads but lacks this formal, map-based zoning with distinct rule sets.
≠ASCE 24 provides a specific, prescriptive formula for flood openings in wet floodproofing (1 sq. inch of opening per 1 sq. foot of enclosed area), while IS 16475 provides general guidance to allow for the entry and exit of water without specifying a quantifiable ratio.
≠ASCE 24 requires materials used below the Design Flood Elevation to be certified as 'Flood Damage-Resistant' based on specific criteria (e.g., withstanding 72 hours of water contact). IS 16475 recommends suitable materials but does not have a formal certification process or a specified test duration for material resilience.
Key Similarities
≈All standards identify elevating the lowest occupied floor above the design flood level as the primary and most effective method for flood risk reduction in new construction.
≈All standards require that structural systems be designed to resist hydrostatic (from standing water), hydrodynamic (from flowing water), and impact loads from flood-borne debris.
≈There is a common emphasis on protecting or elevating building utilities, including electrical systems, HVAC equipment, and plumbing, to prevent damage and malfunction during a flood event.
≈All codes recognize the two primary floodproofing strategies: 'dry floodproofing' (making the structure watertight) and 'wet floodproofing' (allowing water to enter and exit a non-habitable area to equalize pressure).
Parameter Comparison
Parameter
IS Value
International
Source
Minimum Recommended Freeboard
0.3m above Design Flood Level (DFL); 0.5m for important buildings.
Typically 1 ft (0.3 m) or more above the Base Flood Elevation (BFE) as set by local ordinance; higher for critical facilities (e.g., 2 ft / 0.6 m).
ASCE/SEI 24-14
Flood Opening Requirement (Wet Floodproofing)
No specific ratio provided; general guidance to allow equalization of hydrostatic pressure.
A minimum of 1 square inch of net open area for each square foot of enclosed area below the flood level.
ASCE/SEI 24-14
Material Water Resistance Test
Not specified; Annex B lists suitable materials without a test protocol.
Flood damage-resistant materials must withstand direct contact with floodwaters for at least 72 hours without significant damage.
ASCE/SEI 24-14 (via FEMA TB 2)
Dry Floodproofing Height Limit (Guidance)
Recommended for water depths not exceeding 0.9m.
Generally limited to 3 ft (0.91 m) of depth above the floor unless a professional engineer certifies the design for greater depths.
FEMA P-259 / General Practice
Breakaway Wall Failure Load
No specific load value provided; recommends non-load bearing walls be designed to fail under pressure.
Must be designed to fail under a lateral load of not less than 10 psf (0.48 kN/m²) and no more than 20 psf (0.96 kN/m²).
ASCE/SEI 24-14
Location of Flood Openings
No specific height requirement mentioned, just that they should be provided.
The bottom of each opening shall be no more than 1 ft (0.3 m) above the adjacent ground level.
ASCE/SEI 24-14
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Minimum freeboard above Design Flood Level (DFL)0.3 m
Factor of safety against buoyancy (uplift)1.1 (Dead Load / Buoyancy Force)
Unit weight of water (assumed)9.81 kN/m³
Design debris impact load from a log (450kg at 3m/s)4.5 kN (concentrated load)
Maximum flow velocity to consider dry flood proofing1.5 m/s
Key Formulas
Hydrodynamic Drag Force: Fd = 0.5 * Cd * ρ * V² * A
Hydrostatic Force (per unit width): Fh = 0.5 * γw * h²
Buoyancy Force: Fb = γw * Vd
Tables & Referenced Sections
Key Tables
Table 1 - Design Flood Levels
Table 2 - Drag and Lift Coefficients for Hydrodynamic Loads
Table 3 - Debris Impact Loads
Table 4 - Recommended Flood Proofing Measures
Key Clauses
Clause 4 - Site Selection and Planning
Clause 5 - Flood Loads and Load Combinations
Clause 6 - Design of Structural System and Elements
Clause 7 - Flood Proofing and Mitigation Measures
Clause 8 - Materials for Flood Resistant Construction