2. GOOD INDUSTRY PRACTICES – PROCUREMENT
2.1. Early involvement of contractors and MEP specialists
It is important to engage the MEP specialists and main contractor early upfront during the design stage of the project. By incorporating their inputs into the design, a more effective technical solution can be achieved. Design clashes and structural safety concerns due to co-ordination issues can be eliminated. The design of MEP systems will also be more holistic and take into consideration the ease and accessibility of maintenance, replacement and upgrading of such systems.
The Design and Build (D&B) and Design Development and Build (DDB) procurement models facilitate early involvement of the main contractor and MEP specialists during the design stage. This significantly improves the buildability and constructability of the prefabricated MEP design, leading to higher construction productivity.
Design and Build (D&B) model
D&B is a procurement method where the functions of design and construction are placed entirely with the main contractor. Based on the design brief provided by the client, the main contractor will engage his own consultants and the MEP specialists to fully design, develop and construct the development, including the design and installation of prefabricated MEP systems.
Design Development and Build (DDB) model
The DDB model is similar to the D&B model, except that the client will engage his own consultants to develop the conceptual design first. Based on this design concept, the main contractor will work with his own consultants and the MEP specialists to develop the full design and construct the development, including designing and installing the prefabricated MEP systems.
Besides the above procurement models, the consultants, main contractor and MEP specialists can also team up to submit their design to tender for projects.
In the event when early contractor involvement cannot be adopted, the client can consider the following options:
Figure 3: Suggestions for a typical DBB project
Below are examples of overseas procurement models and best practices from the United Kingdom, Japan and Korea.
2.2. Tender requirements and specifications
The requirement to adopt prefabricated MEP modules cannot be an afterthought and needs to be incorporated upfront in the tender documents, starting from the project brief. The early decision to adopt MEP modules in the project allows greater continuity of design and maximises productivity gains.
Project milestones are different when prefabricated MEP modules are adopted in a project. As such, the contract provisions of a project adopting prefabricated MEP modules should take into account the following considerations:
2.2.1. Allow sufficient time to consider design options
During planning, it is important to allocate sufficient time to consider a range of design options for prefabricated MEP modules with the help of BIM software, and avoid rushing into details which can limit the design options.
For example, a detailed design of a building’s services may pre-determine the construction sequence or limit the scope for preassembly. The use of a vertical riser in a frame passing through multiple floors may be more efficient than having a smaller assembly for each floor or fitting components in a traditional in-situ manner.
However, lifting restrictions on the site may prevent this option from being used.
As various design options require inputs across the construction value chain, the client should allow adequate time for design in BIM software and collaboration among its consultants, builder, MEP trade specialists and prefabricator of MEP modules, before construction starts.
2.2.2. Have Co-ordinated Services Drawings (CSD) endorsed by all relevant project parties Once prefabrication is completed, only minor changes are allowed. Any design changes or re-routing causes a lot of disruption.
Hence, it is important that the designs of the MEP services are confirmed early. Since all modules are manufactured based on BIM co-ordinated models, the process of approving the shop drawings is critical and must be robust.
The CSD needs to be endorsed by all relevant project parties i.e. the consultants, builder and relevant MEP trade specialists, according to a pre-agreed schedule.
Clients are also encouraged to require the main contractor and MEP specialists to provide more detailed BIM drawings to facilitate off-site prefabrication of MEP systems.
2.2.3. Approve materials and mock-ups prior to mass production of MEP modules
Unlike cast in-situ works where there is a sequence for materials to arrive on site, upfront material planning is critical for prefabricated MEP modules as all materials are needed at the same time for prefabrication.
Consultants are required to approve the materials used early, so that prefabrication of modules can proceed on schedule. Mock-ups of the most typical prefabricated MEP modules used in the development should also be produced for the consultants’ approval, prior to mass production of the modules in the factory.
2.2.4. Ensure workers are trained and defects are rectified at the factory
The skills of the trade workers deployed at the factory play a critical role in ensuring the smooth installation of modules on site.
To avoid potential disputes, the tender can include requirements for MEP specialist contractors to provide training for workers in the factory, and to rectify defects found in the modules installed on site.
To minimise defects in the modules due to poor workmanship, an engineer’s representative should be engaged by the consultant to inspect the works done in the factory. The engineer’s representative must be an independent party from the prefabricator to avoid conflict of interest.
2.2.5. Improve co-ordination on site and in the factory
Clients can specify to engage firms under the CRS ME15 workhead as the first-level subcontractor to co-ordinate the installation of prefabricated MEP works. The firm should have a relevant track record in the co-ordination and installation of prefabricated MEP modules.
In addition, the tender should specify a dedicated firm or personnel to lead and direct the co-ordination among various trades on site and in the factory. The lead co-ordinator is preferably the builder that is well placed to co-ordinate logistics and activities of all trades on site.
2.2.6. Adopt a different payment certification methodology
With a different work sequence, the contractor’s pricing methodology will change and the consultants’ payment certification methodology and the bill of quantity, or schedule of works in the case of a lump sum contract will also have to be tailored accordingly. For example, if the MEP specialist contractor is also the prefabricator of MEP modules, the MEP specialist contractor can claim part of the contract amount for the modules completed in the factory, before the installation of these modules on site.
The flowchart below shows a possible workflow to implement prefabricated MEP modules in a project. The next few chapters will explore the good practices for each phase of the flowchart.