DED Is Not Just a Technical Drawing: This is the Foundation to Ensure Projects Are Not Miscalculated

Unfortunately, the Detail Engineering Design (DED) is often seen merely as a set of technical drawings that must be "finished first" before the project can proceed. In reality, the DED is the nervous system of a project. Without a proper DED, the Cost Budget Plan (RAB) cannot be trusted, the implementation schedule becomes a baseless estimate, and field supervision loses its reference.

A good RAB is born from a good DED. This is not just a sequence of processes; it is the law of cause and effect in the construction world.

When the BoQ in the DED is inaccurate — for example, if the volume of earth excavation is underestimated, or the area of the painted wall does not include the atrium area — then the figures that go into the RAB are automatically incorrect. The contractor who wins the tender may recalculate on-site and find a significant discrepancy. This is where the requests for addendums, change orders, and cost overruns begin.

Many clients and even consultants think that some parts of the DED can be done "later" or "adjusted in the field." In fact, these five components are the most common sources of problems:

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On the contrary, the vague DED invites different interpretations from each tender participant. One contractor might include the cost of formwork, while another assumes it is already included. The result: a Bid Price (BP) that appears "cheap" may not be due to efficiency, but rather because there are items that were overlooked — and will be charged back through a variation order.

One of the biggest obstacles in realizing a quality Detailed Engineering Design (DED) is the perception that planning consultancy costs are too high. In fact, the logic is very simple:

The cost of creating a comprehensive Detailed Engineering Design (DED) ranges from 2–4% of the project value. Meanwhile, costs for corrections, design changes in the field, and budget overruns due to poor DED can reach 15–30% of the project value. These are not fabricated numbers — this is a reality often experienced by projects in Indonesia.

If you are a project owner, developer, or budget manager, here are concrete things you can do:

• Choose an experienced planning consultant — don't just pick the cheapest one. Track record and portfolio are more important than price.
• Request a clear list of deliverables — the DED must include architectural drawings, structure, MEP, technical specifications, BoQ, and RAB. Ensure everything is included in the consultancy contract.
• Conduct an independent review — ask a supervising consultant or internal team to review the DED before entering the tender phase.
• Don't rush the planning phase — the pressure to start construction quickly often sacrifices the quality of the Detailed Engineering Design (DED). The "lost" time in planning actually saves time in execution.
• Interdisciplinary synchronization — ensure that the architectural, structural, and MEP drawings have been coordinated and that there are no conflicts before the documents are issued.

Start with the right plan, and good construction will follow.