Productivity mapping and literature review
The University of Dundee in association with Whole Life Consultants Ltd was commissioned by the Construction Scotland Innovation Centre (CSIC) on behalf of the AIMCH partners to undertake a wide-ranging literature research analysis and compile a report focused on construction productivity measurement studies and protocols.
The AIMCH project aims to help tackle the UK housing crisis by using industrialised offsite solutions to deliver high quality homes faster, more reliably and at the same cost as masonry-built homes.
The aim of the literature review was to help the AIMCH partners to understand the current landscape of productivity metrics and future trends, and to enable them to gain a good understanding of key tools and techniques in all areas of monitoring. The outputs will be used to inform and influence the way in which the partners choose to measure their on-site activities.
The principal metrics considered were:
- Material waste.
In all, 66 metrics were reviewed.
- 2Productivity including labour productivity;
- 3Quality including rework, defects and reliability;
- 4Cost including cost/m2, cost per unit, cost effectiveness;
- 5Time including duration (normalised to take account of differences in design) and percentage of milestones achieved (including planned completion dates);
- 6Predictability of time and cost;
- 8Material waste.
In all, 66 metrics were reviewed.
Two leading metrics were recommended:
- Percentage of audited items in compliance;and
- percentage of tasks which are pre-planned.
The use of one lagging metric was also recommended:
- Frequency rates, and in particular, number of days of lost work per 100,000 hours worked.
It was further recommended that consideration should be given to supplementing this metric with the number of accident near misses recorded per 100,000 hours worked.
For the measurement of productivity, the following recommendation were made.
- If detailed information about the process of construction, its context and constraints is required, and if the labour force cannot be used to keep the necessary records, then direct, continuous observation by a trained observer should be used; and
- If the purpose is simply to determine the reduction in labour inputs occasioned by off-site manufacture, then the use of radio-frequency identification (RFID) or Bluetooth Low Energy (BLE) technology should be piloted.
In any case, it would be advantageous, not only to the AIMCH project but to the whole industry if RFID were supplemented by direct observations and activity sampling so the relative merits of each approach could be determined in more depth.
For the measurement of quality, the use of the Home Builders Federation Star Rating, the NHBC Quality Rating, and the number of reportable items was recommended.
For cost, the recommended metrics were the average construction cost per plot and the average cost of rectification of defects per plot. To compare the costs of individual elements (eg walls, roofs), it would be necessary to collect construction costs related solely to those elements. To accomplish this, it may well be necessary to carry out direct observations.
TimeThe recommended high-level metric was the average elapsed construction time per plot. If the time required to construct individual elements were the focus of attention, it would be necessary to record the start and completion times of each relevant activity. This may be achieved by the operatives themselves, by supervisors or by intermittent or continuous observations by an independent observer.
Time and cost predictability should both be measured in terms of the average percentage overrun. For complete houses, it should be measured at the plot level (ie average percentage overrun per plot). It can however be measured in the same way for any element or activity in the construction process eg walls, floors, roofs.
It was suggested that metrics describing wastage in labour, plant, material and finance are developed on a case by case basis taking inspiration from lean thinking in sectors such as manufacturing where, for example, the efficiency of a plant is often described by the so called “down time”. When no other viable option is available, the adoption of percentage margin was suggested as an umbrella metric for efficiency whilst recognising that it is also a measure of ‘efficiency’ of the whole process including for instance sales and marketing.
The most relevant metric identified was the net waste measured as the difference between the ‘value of materials not incorporated in the construction works’ and the ‘value of additional recovered materials incorporated in the construction works or in off-site applications’.
The choice of metric is critically dependent on the strategic objectives. Since different organisations have different objectives, it is unlikely that a single set of metrics will find ready acceptance. However, the report provides comprehensive evidence on which to base decisions about which metric should be used in which circumstance.
We recommend that each partner carefully reviews the recommendations we have made together with the underlying rationale, and checks that the metrics proposed satisfy both their strategic objectives and any internal constraints that may apply.