11 Modern Methods of Construction

11.1 MMC Systems

This chapter provides guidance on meeting the Technical Requirements for certification, quality management, site management, installation, verification, and handover requirements for MMC systems used to form homes where the height of the top floor above ground does not exceed 18m. This chapter should be used in conjunction with Chapters 11.2 and 11.3.

Introduction

This chapter gives guidance on meeting the Technical Requirements for certification, quality management, site management (handling, storage, and protection), structural design, structural design checking and certification, installation, verification, and handover requirements for MMC systems used to form homes where the height of the top floor above ground does not exceed 18m.

The guidance in this chapter is intended to outline the common general requirements applicable to MMC systems manufactured in a factory environment. This chapter should be used in conjunction with Chapter 11.2 Closed panel systems and Chapter 11.3 Volumetric systems, where further guidance is given relevant to the system type being employed.

Users of this chapter should also refer to Part 6 of the NHBC Standards, particularly Chapters 6.2 and 6.10 when either timber frame or light steel frame respectively are to be used.

‘Modern Methods of Construction’ is a collective term encompassing a wide range of system types, including off-site manufactured systems that cannot be inspected on site in a traditional manner due to high levels of offsite fabrication, innovative technologies and other non-conventional methods of construction that form the structure and envelop of the home. As such, methods of construction that are described in the preceding chapters of the NHBC Standards, such as open panel light steel and timber frame, and can be inspected on site during the build process are considered as conventional construction rather than MMC.

MMC types have been categorised and defined in the MHCLG Cross Industry Working Group ‘MMC Definition Framework’. The definition framework identifies the following seven MMC categories:

Category 1	Pre-Manufacturing — 3D primary structural systems
Category 2	Pre-Manufacturing — 2D primary structural systems
Category 3	Pre-Manufacturing — Non-systemised structural components
Category 4	Pre-Manufacturing — Additive Manufacturing
Category 5	Pre-Manufacturing — Non-structural assemblies and sub-assemblies
Category 6	Traditional building product led site labour reduction/productivity improvements
Category 7	Site process led labour reduction/productivity improvements

The guidance in this Part will focus on systems that fall under Category 1 ie, volumetric systems, and Category 2 (closed panel only) ie, panelised in the definition framework:

Category 1 — 3D primary structural systems (volumetric)

Three-dimensional structural volumetric units fabricated offsite in a factory environment used to form all or part of the basic structure of a building. Volumetric units may incorporate varying degrees of offsite fabrication and finish, including internal and external linings, external claddings, windows and doors, internal finishes, concealed insulation, membranes, internal services, internal fixtures and fittings and fire-stopping.

Volumetric units can be used in varying configurations to form the entire structure of the home or be supported by surrounding construction. Units can be manufactured in varying structural forms and be formed from timber, concrete, steel or light gauge steel or a combination of those materials.

Category 2 — 2D primary structural systems (panelised)

Flat two-dimensional panelised units fabricated offsite in a factory environment used to form walls, floors, and roof structures. The category encompasses panelised units supplied as ‘open’ or ‘closed’ panel, however the scope of this Part only encompasses ‘closed’ panel systems. Definition of ‘closed’ panel systems is given in Chapter 11.2 Closed Panel.

Definitions for this chapter

Cavity	A space enclosed by elements of a building such as the space between the cladding system and the backing wall. The external wall cavity should be adequately drained, and ventilated where required.
Cavity barrier	A construction within a cavity, other than a smoke curtain, to perform either of the following functions: • Close a cavity to stop smoke or flame entering • Restrict the movement of smoke or flame within a cavity.
Factory installed	An element of the construction that is placed, positioned, fitted, or secured in, on or as part of the unit as part of the factory construction process.
Fire-stopping	A seal provided to close an imperfection of fit or design tolerance between elements or components, to restrict the spread of fire and smoke.
Hold Point	A point in the manufacturing or construction process beyond which work may not proceed until the required inspection and verification has been undertaken.
Installation Manual	Detailed installation guidance and information for the system compiled by the system manufacturer The Installation Manual describes general instructions for storage and transport of the system, and procedures for on-site assembly and installation.
MMC systems	Modern Methods of Construction is a collective term encompassing off-site manufactured systems that cannot be designed or be inspected on site in a traditional manner due to high levels of offsite fabrication, innovative technologies and other non-conventional methods of construction that form the structure and envelop of the home. As such, methods of construction that are described in the preceding chapters of the NHBC Standards and can be inspected on site during the build process are considered as conventional construction rather than MMC.
Manufacturer	The company which is responsible for the design and assembly of the MMC system.
Non-standard components	Components that are assembled as part of the system but vary for individual projects. These may be windows, doors or services that may be built into the system.
Robustness	A quality in a structure/structural system that describes its ability to accept a certain amount of damage without that structure suffering disproportionate failure. Robustness implies insensitivity to local failure.
Standard components	Components that are assembled as part of the system and are common to all projects.
Strong point	A structural element, frame or assembly oriented in a vertical plane that act to resist lateral loads supporting both horizontal and vertical stability systems together with façade (including wind posts, cladding rails, etc) and transfers the lateral actions through the assembly generally down to the foundation. Examples are reinforced concrete shear walls like lift cores or stair wells.
System	For the purposes of this chapter, this term refers to acceptable forms of either closed panel or volumetric MMC systems.
System Manual	Detailed technical information on the system compiled by the system manufacturer. The System Manual describes the system, the declared performance of the system and evidence to support the declared performance.
Unit	A prefabricated building element, manufactured offsite as a structural assembly in three-dimensional or flat panel format used as part of a system to form the superstructure of a building.
Volumetric	Three-dimensional structural units which are commonly stacked to form a building. Volumetric units may incorporate varying degrees of off-site fabrication and finish, including internal and external linings, external claddings, windows and doors, internal finishes, concealed insulation, membranes, internal services, internal fixtures and fittings and fire-stopping.

Clauses for 11.1 MMC Systems

Last updated: 2nd January 2025