Guidelines on the scope and procedures for the review of MMC systems
The NHBC registered builder is responsible for ensuring that the homes they build meet the NHBC Standards regardless of the form of construction. Where MMC systems are proposed, NHBC carries out a review of the system to determine if it can be accepted for use in homes provided with Buildmark warranty.
NHBC undertakes a broad review, taking account of the following headings. Each system should also demonstrate how compliance with Building Regulations is achieved.
Describe the scope of the system along with its intended use and the limits of application, including:
Confirm which parties have responsibility for design and coordination of the system.
Demonstrate structural performance of the system against appropriate relevant and recognised standards. This will usually comprise a design philosophy statement that describes how loads are sustained and transmitted to the ground. The statement should include:
Where the MMC system is manufactured off site, an assessment of the performance of the structure under the temporary loads during transportation and erection is expected.
Demonstrate the performance of the system in relation to fire. Particular consideration to be given to:
Demonstrate how the system prevents moisture ingress to the home from the ground and from precipitation and how the risk of interstitial condensation is mitigated.
Demonstrate how the MMC system provides adequate sound resistance:
Demonstrate how the MMC systems reduce energy use in the building:
Demonstrate that the materials used are suitable for their intended purpose and that the structure of the home has a design life of at least 60 years. The measures taken to protect the materials should be specified. Methods of demonstrating acceptable performance include:
All interfaces should be considered within the system and how the system fits with the rest of the building to form the home. Standard details should be provided by the system supplier to demonstrate how the system can be used in different configurations, including:
Demonstrate how the factory production control systems can ensure the prefabricated elements are manufactured to the design described in the system manual and that measures are in place to enable the system to be constructed to the design. This should include:
The review process normally comprises three stages:
The MMC manufacturer submits technical information to NHBC for an initial review. We review the system to determine if it appears broadly in principle to be capable of meeting the performance criteria. We will assign a Technical Officer or Engineer to lead the review and provide an initial gap analysis indicating whether further information is needed.
The MMC manufacturer submits detailed technical information in the form of a system manual. The system manual is a comprehensive document that describes the system, the declared performance of the system and evidence to support the declared performance.
The system manual also describes the method of assessment of manufacturing quality management and Factory Production Controls (FPC).
Subject to satisfactory completion of the detailed review, the system can be used on a pilot project. The pilot project is to demonstrate the use of the system in a small number of homes (typically no more than four) on a registered NHBC site. The NHBC registered builder is responsible for ensuring that the homes built on the site meet NHBC’s technical requirements and the process of providing warranty is the same as in all other NHBC registered homes.
If the pilot scheme demonstrates that the design intent can be realised, the MMC system will be listed as an accepted system on the MMC Hub.
The system manual is a comprehensive document that describes the system, the declared performance of the system and evidence to support the declared performance. The system manual also describes the method of assessment of manufacturing quality management and Factory Production Controls (FPC).
Systems manuals can take one of two forms:
The system manual should contain:
A system manual should reflect the particular characteristics of the system and there is no defined format. However, the typical contents expected for manuals for some more common MMC systems are found below for guidance. Please contact NHBC’s Standards, Innovation and Research team to discuss the contents of the system manual for a new MMC system.