skip to content

Laing O'Rourke Centre for Construction Engineering and Technology

Methodology for quantifying the benefits of offsite construction

CIRIA and the Laing O’Rourke Centre for Construction Engineering and Technology, University of Cambridge, have launched a new guidance framework to unlock evidence-based assessments of offsite construction and data driven decision-making for the industry. The guide urges the construction industry to unify project performance monitoring by applying a consistent methodology.

Offsite construction offers the potential to deliver a variety of benefits including better quality construction, improved health and safety, a faster construction programme as well as predictability of cost and time on a project. Despite this, uptake of offsite construction is slow and there is limited objective, evidence-based research to validate these suggested benefits.

The CIRIA guide C792, launched on 16 March, proposes a methodology for evaluating project performance with the intention of identifying how construction approach influences project outcomes and whether offsite construction delivers the expected benefits.

This guide is the result of a year-long research project by CIRIA and the Laing O’Rourke Centre for Construction Engineering and Technology, University of Cambridge. The research team were advised by a project steering group (PSG) comprising 27 organisations from across the construction industry to ensure the relevance of the proposed methodology for industry.

The resulting publication describes the process of identifying and measuring relevant metrics that may be influenced by offsite construction and then applies the proposed methodology to a set of case study projects to evaluate how construction approach influences project performance.

The data and analysis highlight the challenges that can be expected when assessing the performance of construction projects and developing robust benchmarks for comparison. The report speaks directly to these challenges by proposing a framework which would enable the industry to:

  • Keep consistent records across projects and companies.
  • Assess the value and benefits achieved on projects.
  • Establish a database on project performance.
  • Facilitate wider collaboration.

Identifying relevant metrics for measurement

The first step of this project sought to identify the expected benefits of offsite construction and how to measure them. Apart from the upfront construction impacts, it was important to include broad impacts beyond just capital cost, addressing environmental and societal factors such as local disruption and workforce quality of life. The guide identified metrics to quantify the project’s impact on each factor, and defined the boundaries of assessment to ensure metrics can be consistently measured across different projects or organisations.

These metrics, together with the guidance for measuring them, form a methodology that project stakeholders can use to assess the value and benefits achieved on projects and determine if offsite construction delivered the expected benefits.

These metrics were devised in collaboration with industry and, wherever possible, existing methods of measurement were used to encourage uptake of the methodology. However, the research highlighted the wide range of metrics already in use in industry and the many variations used by organisations for assessing project performance. Even through direct engagement with the PSG, it was not possible to reach agreement on the most important metrics to measure nor how to measure them.

Already this first step hints at the challenges to be expected when comparing project performance across different projects and companies.

Testing the methodology on school projects
The research team tested the implementation of the methodology by analysing case study projects. Crucially, these case studies assess project outcomes by systematically reviewing data from completed projects, rather than describing hypothetical relative benefits that could be expected when implementing an offsite construction approach instead of a traditional approach. By collecting actual results from a range of projects, the aim is to establish an evidence base to assess the benefits of offsite construction.

To narrow the focus and provide meaningful results, projects were selected from a specific sector. The team chose the education sector because of the established use of offsite construction in schools projects, meaning there may be more easily accessible information on completed projects with a variety of  construction approaches. By engaging with the PSG and other interested parties, we received and analysed data from 46 completed school projects across the UK, featuring different levels of offsite construction and variations in scale, location and build approach. Six different organisations supplied data and their engagement demonstrates a willingness to collaborate to improve the performance of the construction industry. We are grateful for their input.

Key findings of the research
The research process highlighted the many challenges to be faced when attempting to evaluate project performance in the construction industry, as well as specific challenges to do with quantifying the benefits expected from offsite construction. While setting up the metrics, it became ;apparent that in many cases the relevant information, that would be required to quantify the impact, is simply not collected. Without such information it is not possible to determine whether there truly is benefit to be gained from an offsite construction approach. For example, several papers mention that offsite construction reduces vehicle movements to site. However, in practice, this information is not generally collected on construction sites - meaning it was not possible to verify this benefit.

It also became evident that there are differences between what is ideal to measure and what is practical to measure based on the data available. For example, to assess the build quality of a project and the extent of construction defects, it would be useful to know the cost of rework ;undertaken as a result of design or construction errors. However, from discussions with industry it is apparent that information about the cost of rework required on a project, and root cause thereof, is not routinely collected. An established metric, in general use within the industry, is the number of defects that emerge during the defects liability period. However, this alone is a poor indicator for evaluating build quality as the type, extent and knock-on effects of the defect are unknown.

When analysing the case study project data, the first hurdle involved establishing a consistent method for assigning the extent or maturity of application of offsite construction methods on each project - generally referred to as the ;Pre-Manufactured Value (PMV). Recognising that ‘offsite’ and ‘traditional’ construction is not a simple either/or scenario but rather a spectrum of application of different systems, technologies and products, a qualitative ranking was used to categorise projects as high, medium or low PMV. This was due to difficulties in obtaining sufficiently detailed information from projects to quantitatively calculate the PMV using current industry methods.

Further findings of the research highlight the challenges faced in establishing robust benchmarks for performance of construction projects. The lack of availability and consistency of project data means that there is no coherent approach for measuring project performance and outcomes in the construction industry. This applies to projects across the spectrum from traditionally constructed projects to those with high levels of offsite construction. The data and evidence gathered need to be more consistent across the industry to demonstrate the benefits of offsite construction.

A challenge to the construction industry
The research highlights the difficulties in creating robust evidence of project performance in the construction industry and correlating project outcomes and results with construction methodology. In response to these challenges, the report serves as a call to action and change, and outlines a way forward. The metrics and methodology described in this guide provide a consistent approach for ;evaluating project performance on completed projects. Adopting this methodology across the industry would start the process of creating an evidence base that can be used to understand the correlation between construction approach and the benefits that could be expected, thereby supporting decision-making on projects and policy relating to offsite construction.


The guide is available to download freely from: