Modern methods of construction: guidance for building standards verification

Provides guidance to Local Authority verifiers and Certifiers as defined under the Building (Scotland) Act 2003 when assessing building warrant applications and certifying works which use Modern Methods of Construction (MMC).

4. Factory assembly

4.1. General

  • The verification of building warrant construction works carried out in a factory potentially significantly remote from the construction site can be problematic and particularly in the case of closed panel and volumetric construction. During the onsite construction/assembly phase of a project, these methods by their closed panel nature reduce the opportunity for verifiers to readily inspect internalised construction hidden from view. Verifiers have visited factories for this purpose when practical/ considered necessary to do so.
  • This section identifies potential risks and other assurance methods that may be considered.
  • As indicated in Section 2, STAS is beneficial in achieving a national decision on compliance accepted by all 32 authorities appointed as verifiers. This outcome may be particularly beneficial if applied to the factory assembled process of MMC where the assessments can be carried out once at the geographical location of the assembly plant, through the STAS process rather than by 32 authorities.

4.2. Potential risks: manufacture and quality assurance in the factory

  • There is a risk of product substitution[12] i.e., deviation from the drawings and details provided in the building warrant application.
  • Defects in manufacturing may occur in the absence of a clearly defined and robust quality assurance process and other relevant controls.
  • Bespoke systems may not have quality assurance procedures in place, making it more difficult to assess quality.

4.3 Factory assembly: considerations for verifiers and certifiers of construction


  • Is there is evidence of quality-controlled systems for factory production (MMC accreditation such as BOPAS, NHBC Accepts would provide assurance that this has been assessed) which may provide evidence of compliance with design specification
  • In the absence of MMC accreditation, is there is evidence of the factory's quality assurance and inspection processes and controls subject to review/audit – for example ISO 9001.
  • Particularly in terms of closed panel and volumetric systems - do the quality-controlling systems in place provide sufficient evidence and assurance of building warrant compliant construction in areas that will not be available for inspection on site? A physical or virtual factory/process inspection or photography/videos may provide further assurances – see Section 4.1 General above.



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