Overview
ISO 21723:2019 - Buildings and civil engineering works - Modular coordination - Module defines the standardized module system used to coordinate dimensions in building design and construction. The standard establishes the basic module (M = 100 mm), a set of preferred multimodules for horizontal coordination, preferred vertical modular dimensions, and sub‑modular increments. It is intended to harmonize sizing of components, spaces and building systems to improve interchangeability, economy and clarity in design and production.
Key topics and technical requirements
- Basic module
- 1 M = 100 mm (international metric value). Annex A gives the imperial equivalent (4 in = 101.6 mm) for countries using imperial units.
- Multimodules for horizontal coordination
- Standard multimodules: 3 M, 6 M, 12 M, 30 M, 60 M.
- 15 M may be used for special applications.
- A series of preferred multimodular sizes (Table 1) guides selection; preference is given to the largest multimodule compatible with function and economy.
- Vertical modular dimensions
- Modular storey and room heights use defined increment steps: up to 36 M in 1 M steps; 36–48 M in 3 M steps; above 48 M in 6 M steps.
- The relationship between modular storey height, modular floor height and modular room height is specified (modular floor plane positions illustrated).
- Sub‑modular increments
- Standard value: M/2 = 50 mm.
- Allowed for sizing components smaller than 1 M or for finer increments when needed. Not permitted to define distances between primary modular reference planes but may be used to displace modular grids for whole‑project alignment.
Applications and users
ISO 21723:2019 is practical for:
- Architects and building designers applying modular coordination to layouts and room planning.
- Structural and MEP engineers for consistent component sizing and clear interface dimensions.
- Manufacturers of building components and prefabricated systems to ensure products fit modular spaces.
- Contractors and fabricators using modular grids for efficient assembly and offsite construction.
- BIM modelers, planners and standards bodies seeking standardized dimensional rules for interoperability.
Benefits include improved coordination, reduced waste, simplified manufacturing tolerances, and easier integration of prefabricated elements.
Related standards
- ISO 2848 - Modular coordination: principles and rules
- ISO 8560 - Representation of modular sizes, lines and grids (technical drawings)
- ISO 6707-1 - Building vocabulary (terms)
- ISO 1791 (legacy vocabulary source referenced)
ISO 21723:2019 consolidates earlier ISO modular standards into a single, practical reference for dimension coordination in building and civil engineering works.
