The decision making process used to evaluate to what extent a component or building system should be produced off-site is inadequate within the industry. Whilst the potential benefits of off-site production (OSP) are commonly cited when justifying an OSP approach, no clear method for assessing the applicability and overall benefit of these solutions exist. Common methods of evaluation simply take material, labour and transportation costs into account when comparing various options, often disregarding other cost-related items such as site facilities, crane use and rectification of works. These cost factors are usually buried within the nebulous preliminaries figure, with little reference to the building approach taken. Further, softer issues such as health and safety, effects on management and process benefits are either implicit or disregarded within these comparison exercises. Additionally, the factors that affect the suitability of OSP as a design solution are not formally defined, these are the factors that drive and/or constrain the design decision making. Case based research funded by the UK Engineering and Physical Sciences Research Council and Department of Trade and Industry in collaboration with eleven companies sampling over 200 people employed within the construction industry, examined these issues and developed a toolkit under the name IMMPREST4 • This toolkit facilitates the evaluation of the potential benefits of choosing one approach over the other.
Pre-assembly, off-site production, drivers, constraints, benefits, measurement, value