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IS 7921:1987 is the Indian Standard (BIS) for recommendations for modular coordination in the building industry: horizontal co-ordination. This standard provides recommendations for horizontal dimensional coordination in the building industry. It establishes a system based on a basic module (100 mm) and a multi-module (300 mm) to rationalize and standardize the dimensions of buildings and their components, facilitating prefabrication and design efficiency.
Recommendations for modular coordination in the building industry: Horizontal co-ordination
Overview
Status
Current
Usage level
Specialized
Domain
Architectural — Planning, Housing and Pre-fabricated Construction
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! The 300 mm (3M) grid is the most practical and widely adopted planning grid for setting out column lines and major building elements.
! This code is foundational for pre-cast and prefabricated building systems, ensuring components from different sources can integrate.
! Understanding the difference between 'co-ordinating size' (grid-to-grid) and 'work size' (actual component size) is crucial for applying this standard correctly.
ISO 1006:2017ISO (International Organization for Standardization)
HighCurrent
Building construction — Modular coordination — Basic module
Defines the fundamental 100 mm basic module (M), which is the cornerstone of IS 7921.
ISO 2848:1984ISO (International Organization for Standardization)
HighWithdrawn
Building construction — Modular coordination — Principles and rules
Provided the overall principles and rules for modular coordination that IS 7921:1987 is based on.
ISO 1040:1983ISO (International Organization for Standardization)
HighWithdrawn
Building construction — Modular coordination — Multimodules for horizontal coordinating dimensions
Directly corresponds to the scope of IS 7921 by specifying preferred multimodules for horizontal planning.
BS 6750:1986BSI (British Standards Institution), UK
HighWithdrawn
Specification for modular co-ordination in building
A comprehensive national standard implementing the same ISO principles as IS 7921 for the UK market.
Key Differences
≠IS 7921:1987 is an active standard but is based on principles from the 1980s, whereas its direct international counterparts (like ISO 2848 and ISO 1040) have been withdrawn and replaced by a more modern, integrated series of standards (e.g., ISO 21723).
≠The Indian standard is a standalone document for horizontal coordination. The modern ISO framework is a larger, more interconnected system with separate standards for basic modules, terminology, and principles, often better integrated with modern concepts like BIM.
≠IS 7921 does not explicitly detail the 'neutral zone' concept for component placement relative to grid lines as thoroughly as some modern international guidelines, which provide more specific rules for tolerances and joints.
Key Similarities
≈The fundamental building block in both IS 7921 and the international standards is the basic module 'M', defined as 100 mm.
≈Both systems are built on the principle of a three-dimensional reference grid, with IS 7921 focusing on the horizontal plane, for positioning building elements and components.
≈The set of preferred horizontal multi-modules (e.g., 3M, 6M, 12M, 30M, 60M) recommended in IS 7921 is identical to those specified in the historically equivalent ISO 1040:1983.
≈The core objective is the same: to rationalize building dimensions, promote the interchangeability of prefabricated components, simplify construction processes, and reduce material waste.
Parameter Comparison
Parameter
IS Value
International
Source
Basic Module (M)
100 mm
100 mm
ISO 1006:2017
Primary Horizontal Planning Module
3M (300 mm)
3M (300 mm)
ISO 1040:1983
Series of Preferred Horizontal Multi-modules
3M, 6M, 12M, 15M, 30M, 60M
3M, 6M, 12M, 15M, 30M, 60M
ISO 1040:1983
Basis for Dimensioning
Multiples of the basic module (n x M)
Multiples of the basic module (n x M)
ISO 2848:1984
Use of Sub-modular Increments
Permitted in special cases (e.g., M/2, M/5 for small components)
Permitted for specific conditions, such as thin components or joints (e.g., M/4, M/2)
ISO 2848:1984
Reference System
A rectangular co-ordinate grid in the horizontal plane
A system of reference lines and planes forming a 3D grid
ISO 2848:1984
⚠ Verify details from original standards before use
What is the basic module 'M' for modular coordination?+
The basic module 'M' is 100 mm (Clause 3.1).
What is the recommended multi-module for horizontal planning?+
A multi-module of 3M (300 mm) is recommended for horizontal co-ordinating dimensions (Clause 3.2).
What is a modular grid?+
It is a grid in which the spacing of lines in both directions is a basic module (M) or a multi-module (Clause 2.13).
How should structural grids relate to modular grids?+
Structural grids should be based on the modular grid, typically using multi-modules like 3M, 6M, or 12M for spacing columns and load-bearing walls (Clause 4.3).