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MMC Hub

The resource centre for offsite and other non-conventional construction

Apply for review

NHBC’s review process is aimed at ensuring MMC systems and sub-assemblies demonstrate an acceptable level of performance in order to satisfy the requirements of NHBC Technical Standards. The principles of the procedure are based on NHBC Standards Chapter 2.1 The Standards and Technical Requirements. Where building systems and elements are assembled from factory made components, the manufacturer will be required to demonstrate that they have been manufactured under a quality management system, such as ISO 9001 and achieve a consistent standard of performance as set out in NHBC standards.

The web-form and downloadable documents below provide you with a step-by-step guide through the application process and outline the information NHBC require.

Contact details

NHBC's normal working hours are 8:30am to 5:30pm, Monday to Friday

Manufacturer address

System information

Suitability of building systems or elements to meet NHBC warranty requirements

Reference should be made to NHBC Standards, chapter 2.1, Technical Requirements R2, R3 and R5 and relevant chapters of the standards for which the system or product may be applicable and satisfy requirements.

Has the system or element been assessed and certified by a notified body that recognises UK Building Regulation requirements and warranty standards?

Any independent assessment should provide details of the technical investigations and testing that have been carried out to verify performance in the following critical areas:

  • Strength and stability

  • Thermal performance

  • Air permeability

  • Behaviour in relation to fire

  • Resistance to airborne sound

  • Resistance to moisture

  • Risk of condensation

  • Durability and longevity of materials

  • Compatibility of materials and interaction between components

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System Manual

A system manual should be provided and the information contained should be in English. The system manual should give a full description of the system or element and define its scope of application.

Care must be taken to ensure that the Construction meets relevant Building Regulations, NHBC Standards, British Standards, Eurocodes and (or) statutory requirements on a site-by-site basis.

The system manual should consider and demonstrate how the performance of the following critical aspects are verified in reference to the relevant parts of NHBC Technical Standards:

Strength and stability:

  • Structural performance should be identified against appropriate, relevant and recognised standards by the system and (or) element manufacturer's chartered civil or structural engineer.

  • Please provide details of the structural design philosophy: structural design calculations to quantify dead and imposed loading, diaphragm action of ceiling and floor, diaphragm action and racking resistance of wall panels, wind loading and other actions, to evaluate and verify structural capacity and compliance with disproportionate collapse requirements.

  • Please provide a clear definition of the role and responsibility of the manufacturer’s chartered civil or structural engineer who is accountable for the structural design. This includes interfaces of the system or element to site-specific items that are the responsibility of the project engineer such as connections to foundations, wall panel, wall plate etc.

  • Example calculations of building systems or elements carried out by the manufacturer’s chartered civil or structural engineer should be provided in the appendix of the manual.

Condensation risk:

  • Thermal properties and measures to prevent condensation.

  • Vapour permeability of external walls and roofs.

  • Compliance with NHBC standards part 6 and BS 5250 Control of condensation in buildings.

  • Analysis in accordance with BS EN 13788 (Glaser method) using boundary conditions of > 60% internal RH at 21°C and external temperature of -2°C.

  • Any remaining conditions should be derived from statistical data e.g. BS 5250 Code of practice for control of condensation in buildings.

  • Condensation risk assessments based on hygrothermalanalysis in accordance with BS EN 15026 can also be considered.

Durability:

  • Durability and longevity of materials, protection of individual components i.e. galvanising zinc protection of LGS, high or low vacuum preservative treatment of solid timber in order to achieve the required 60 year lifespan of the structure.

  • Individual components and assemblies not integral to the structure may have a lesser durability and need planned maintenance, repair or replacement during that period.

  • Detailed designs in order to manage moisture ingress and vapour movement including the use of suitable dpcs, dpms, vcls, breather membranes and flashings to ensure suitable performance.

Interfaces:

  • Full details of how joints and junctions are formed.

  • Full details of any interfaces between modular units and other components in the building that may not be under the control of the modular manufacturer.

  • The responsibility for design and coordination should be clearly identified along with ownership at installation.

  • Off-site & on-site interfaces including foundations and services.

  • Installation tolerances including line & level.

  • Resistance to moisture including the interface between the superstructure and the foundation.

  • Resistance to gas (including radon where appropriate) and how precautions interface with other parts of the building.

  • Type of cladding and how it is supported.

  • Type of generic façade systems entirely placed on-site using conventional techniques, completely or partially attached in the factory.

  • Interfaces with window and door openings (head, cill, jamb details)

  • Differential movement between the cladding and the modular structure should be taken into account. For self-supporting cladding, any components attached to the modular structure that protrude into or past the external cladding (window cill, vent, overflow pipe) appropriate gaps and/or sealed movement joint/s to allow for the calculated movement should be detailed.

  • Service interfaces: installation of electrical, plumbing and heating services in modular buildings installed in the factory with final connections made on-site, including details of; service layout, ducts (including access) within the modules, distribution of services between modules, drainage and other external services

Building Regulation compliance:

  • Confirmation that the system is compliant with the appropriate Building Regulations or standards.

  • Note: this framework does not provide agreement to compliance with Building Regulations, however details of compliance should be provided in the system manual.

Quality management system:

  • Production process and quality control procedures.

  • Quality management system in accordance with the requirements of BS EN ISO 9001: 2008.

  • Method statement of on-site assembly and QA including permitted tolerances.

  • Details of the auditing and certification of the QMS.

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Previous Step

MMC System Review

The Builder is responsible for ensuring that the homes they build meet the NHBC Standards regardless of the form of construction. To support builders intending to build with MMC, NHBC carries out a review of MMC systems as described in the manufacturer’s system manual against key performance criteria.

NHBC undertakes a broad review, taking account of the points listed below. Each system should also demonstrate how compliance with Building Regulations is achieved.

1. Scope and design responsibility

Describe the scope of the system along with its intended use and the limits of application, including:

  • Applicable geographic location
  • The building regulations that apply
  • Ground conditions, wind loading and storey height limitations

Confirm which parties have responsibility for design and coordination of the system.

2. Strength and stability

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:

  • List of design standards and other sources of reference
  • Materials design parameters, deflection limits, movement & tolerances
  • Loadings and description of load path and overall stability and the provision of any movement joints
  • Drawing and calculations of primary structural systems
  • Details of the design provisions made to prevent disproportionate collapse
  • Assessment of the fire resistance of the structural elements.
  • Dynamic performance criteria (where required)

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.

3. Behaviour in relation to fire

Demonstrate the performance of the system in relation to fire. Particular consideration to be given to:

  • Internal fire spread (linings). Evidence of how the internal linings provide adequate resistance to the spread of flame over their surfaces and if ignited that they have a reasonable rate of heat release or rate of fire growth
  • Internal fire spread (structure). Evidence of how the stability of the building is maintained for a designated period in the event of fire and how the spread of fire is inhibited within a building and between adjacent buildings
  • Specification and design details of fire stops and cavity barriers that demonstrates they have adequate resistance to fire and smoke
  • Details of the materials used and their behaviour in fire together with the fire test data of those materials (tested in the configuration in which they are proposed to be used).

4. Resistance to moisture

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 resistance to moisture from the ground including the use of suitable damp proof membranes, damp proof courses and other separation of the structure and internal environment from ground moisture.
  • Demonstrate how the building envelope resists the passage of water into the home. This should include management of moisture ingress and vapour movement including the use of flashings, vapour control layers and breather membranes. Drained and vented cavities are required in all external timber framed walls.

5. Resistance to the passage of sound

Demonstrate how the MMC system provides adequate sound resistance:

  • Between adjoining homes (through party walls and floors)
  • Within the home (internal walls and floors)
  • From outside of the home (through external walls)
  • Around soil pipes

6. Energy efficiency

Demonstrate how the MMC systems reduce energy use in the building:

  • Through heat losses and gains through walls, floors, roofs, windows etc.
  • From heating and ventilation services
  • Around soil pipes

7. Durability of materials

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:

  • Performance in accordance with the NHBC Standards
  • Compliance with relevant British Standards or equivalent European Technical Specification
  • Satisfactory assessment by an appropriate independent technical approvals authority
  • Use of materials and products in accordance with well-established satisfactory custom and practice accepted by NHBC.

8. Interfaces, compatibility of materials and interaction between components

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 settings, including:

  • Details of how joints and junctions are formed, including consideration of vertical steps and horizontal staggers in the building plan or elevation
  • Interfaces between elements manufactured off-site and on-site construction, including services, foundations and methods of protection of the home from ground gasses
  • Type of cladding or façade systems, how they are supported and details of their assembly and/or finishing on site
  • Interfaces with window and door openings (head, cill, jamb details) and other openings in the building envelope.
  • Detailing to account for thermal movement and the differential movement between different materials and structural elements

9. Quality assurance and production controls

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:

  • Audit of the factory production controls and quality management systems carried out by a third party, acceptable to NHBC
  • Method statement for packaging, transport and on-site assembly
  • List of on-site checks to manage QA at delivery and during erection of units

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