Case Studies of Successful Preliminary Design: Practical Points Learned from Projects

What Is Preliminary Design: Reviewing the Basics and Roles

"Preliminary design" refers to the rough design and cost estimation carried out in the early stages of a project. In this phase, plans are drawn up and rough construction costs are calculated based on limited information; this stage is a vital step in guiding plans to success across fields such as architecture, civil engineering, equipment, and urban development. By understanding the project scale, specifications, and budget frame before proceeding to detailed design (working drawings), feasibility can be evaluated and stakeholder consensus built. The role of preliminary design is to set the overall direction of the project and prevent rework in later stages. If a high-accuracy preliminary estimate can be produced early, budget overruns and major design changes later on can be avoided. Recently, there have been increasing cases in the construction industry where projects have been forced to be reexamined due to budget overruns at the bidding stage, so improving preliminary estimate accuracy upstream is being emphasized again. Moreover, due to material price surges, the number of public works projects experiencing failed bids (zero bids) or bids exceeding the planned price has increased in recent years, highlighting anew the importance of improving accuracy at the preliminary stage and of flexible design revisions. This is especially a compass for small- and medium-sized design offices and general contractor design departments to carry projects forward with limited resources. In projects involving government agencies, preliminary design documents serve as the basis for budget approval and decisions on project implementation, so highly reliable preliminary design is required.

Case Study 1: Architecture (Structural Revision from Timber to RC Due to Change of Use)

In a local government public facility plan, the original assumption was a single-story timber building with a total floor area of approximately 1,200 m². Planning with timber aimed to reduce construction period and cost, but during the planning stage the facility's use changed. With an added role as a regional disaster-prevention hub, a structure with higher durability and fire resistance was required, and the design team suddenly had to consider changing from timber to reinforced concrete (RC) construction. However, switching to RC is generally said to increase construction costs to about 1.5 times those of timber. As expected, keeping the same scale and functions but changing to RC made the preliminary construction cost projections greatly exceed the original budget. For example, while the preliminary cost for the timber plan was about JPY 200 million, changing to RC for the same scale was estimated at over JPY 300 million, which far exceeded the budget (about JPY 220 million). Therefore, the designers and cost managers returned to the basic planning stage and began design revisions to absorb the cost increases associated with the structural change. Specifically, they reduced low-necessity ancillary spaces to compress the total floor area to about 1,100 m², and reorganized the structural design into a simpler grid layout. They also avoided overly expensive finish materials and reviewed specifications to balance cost while ensuring durability. As a result of multiple rounds of plan and cost alignment (revision flow) during the preliminary design stage, the RC plan after the change of use was brought within the original budget (within about +5%). By flexibly reworking the design early and continuously updating cost estimates, they were ultimately able to produce a plan acceptable to all stakeholders. Additionally, changing the structure to RC improved seismic resistance and durability, meeting the new functional requirements. This project is a good example of the importance of meticulous cost consideration and adjustment during preliminary design.

Case Study 2: Civil Engineering (Route Revision at the Preliminary Design Stage of a Road Improvement Project)

In a rural road improvement project, it became clear that the initial planned alignment did not sufficiently account for on-site terrain conditions. On drawings the shortest route was drawn straight, but during the preliminary design stage, detailed site survey data revealed a small valley along the route that concentrates water during heavy rain. If construction proceeded as planned, large volumes of embankment or large drainage structures (such as box culverts) would be required later, risking cost escalation and schedule extension. The design team reviewed the plan during the preliminary design stage and revised the alignment to reflect terrain and drainage planning. Specifically, they shifted the alignment to follow a gentle ridge to avoid the problematic valley, reducing elevation differences and significantly cutting the need for large-scale earthworks. At the same time, they incorporated the necessary drainage facilities (side ditches and drainage channels) into the design in advance, simulated stormwater flow paths, and included appropriately sized drainage structures in the preliminary design. This route change and drainage plan revision significantly reduced earthwork volumes, and was estimated to produce cost savings of several tens of millions of yen on the basis of the preliminary construction cost. As a result, the preliminary estimate included drainage countermeasure costs that had initially been overlooked, avoiding later requests for additional budget. Design changes after the detailed design stage were minimized, and coordination with local stakeholders proceeded smoothly. Incorporating terrain conditions and drainage planning at the preliminary design stage reduced project risk and enabled smooth construction—an illustrative success. Furthermore, this improvement reduced drainage failure risk for communities along the route, providing desirable environmental and disaster-prevention benefits.

Case Study 3: Equipment (Existing Condition Survey and Construction Method Innovations in Renewal of an Aged Pump Station)

There was an urban infrastructure renewal project to refurbish an aging drainage pump station. When modernizing a pump station several decades old, the initial plan considered demolishing and removing the existing facility and rebuilding a new pump station from scratch. But when a preliminary estimate was calculated, demolition and removal costs plus new construction costs were found to far exceed the budget. In addition, because drainage functions could not be suspended for a long time, the cost of installing temporary pumps during construction was also a significant concern. Therefore, the design team conducted a detailed survey of the existing pump station at the preliminary design stage. Diagnosing the structural frame and piping systems revealed that some concrete tanks and foundations could be reused with reinforcement. Considering the existing pump layout and space, they examined a construction method that would leave parts of the existing building and update equipment in stages. Specifically, they planned a temporary platform allowing old and new pumps to be installed in parallel and switched sequentially to minimize pump outage periods. As a result, by choosing a refurbishment plan that utilized existing assets rather than a full rebuild, they were able to greatly reduce the preliminary construction cost compared to the initial plan. Ultimately, about a 30% cost reduction was achieved at the preliminary stage, and costs for temporary equipment were included in the preliminary estimates to avoid later additional expenses. Through prior investigation and construction-method innovations, the aging equipment was renewed within budget while minimizing impacts on citizens' lives—a good example. In addition, effectively reusing existing structures reduced waste generation and contributed to lowering environmental impact.

Case Study 4: Urban Development (Initial Preliminary Estimates Including Land and Infrastructure Costs in a Redevelopment Project)

This is a case of an urban redevelopment project. In a station-front area, a plan was launched to redevelop aging buildings and construct a mixed-use building with commercial facilities and residential towers. While the building construction costs themselves are huge, land acquisition costs and surrounding infrastructure development costs are even more critical to the project's viability. For example, land acquisition costs in this district were estimated at over JPY 12 billion compared to building construction costs (hypothetically JPY 10 billion), accounting for more than half of the total project cost. If these costs were not accurately incorporated in the preliminary design from the start, land acquisition or road improvement costs could fall short later and the entire project might stall. Therefore, the developer and administrative departments responsible for the project compiled detailed initial preliminary estimates from the planning stage. Specifically, they investigated demolition costs and eviction compensation required to clear the site, and acquisition costs for dozens of land parcels, and reflected these in the total project cost early on. They also coordinated with related agencies to include estimates for new roads, water and sewer, and power infrastructure in the preliminary calculations. Because these costs have greater uncertainty compared to building construction costs, contingency funds to cover risks were also included in the initial preliminary estimates. Thanks to such comprehensive preliminary design, the total project cost increased compared to initial assumptions, but having a realistic figure early enabled prompt revision of financial planning and the project scheme. As a result, flexible measures such as securing additional financing or splitting project phases became possible, and the project has progressed without major problems. Presenting realistic numbers from the outset also helped build trust with local residents and investors, facilitating smoother procedures. This case demonstrates that in urban development, preliminary design that considers land acquisition and infrastructure costs from the initial stage is a critical factor that can determine a project's success or failure.

Common Innovations and Checkpoints Across the Cases

From the above cases, we can distill common innovations and checkpoints at the preliminary design stage.

• Thorough on-site surveys and information gathering at the initial stage: Understanding site realities and the condition of existing assets at the outset reduces unforeseen issues later. It is important to identify terrain, building conditions, applicable laws and regulations, and other information early.

• Consideration of cost-conscious alternatives: Compare multiple plans together with preliminary estimates and seek options with better cost performance. When necessary, do not hesitate to propose alternatives such as scale reduction or specification changes.

• Close communication with stakeholders: Hold meetings with owners and related agencies from the early stages to share goals and constraints. If signs of budget overruns appear, report them promptly and discuss countermeasures to facilitate smooth consensus building.

• Identification of risk factors and inclusion of contingency funds: Identify uncertainties and potential risks and reflect them in preliminary costs. Consider often-overlooked items such as land costs, temporary facilities, and price fluctuation risks at this stage, and set contingency funds with margin.

• Utilization of specialist knowledge and digital tools: When necessary, draw on the expertise of cost engineers and structural specialists, and use the latest tools to collect high-accuracy data and run simulations. This further enhances the reliability of preliminary design.

Use of Digital Tools and Simple Surveying

Recently, digital transformation (DX) has surged into the construction and design fields, and preliminary design can also benefit from it. Particularly for site understanding and quantity takeoff, the use of modern digital tools and simple surveying devices is gaining attention. For example, terrain surveys that previously required specialist surveyors can now obtain detailed terrain models in short time using small drones for aerial photogrammetry or 3D laser scanners for point-cloud measurement. In building interior renovation plans, 360-degree cameras and smartphone-compatible laser distance meters can instantly capture as-built dimensions, and such cases are increasingly helping initial planning. In addition, advances in design software are streamlining preliminary tasks. For instance, using BIM (Building Information Modeling) allows automatic quantity takeoffs from initial models to quickly produce preliminary estimates. AI-based estimating tools that leverage past project data have also emerged, enabling designers to refine plans while grasping costs in real time. One of the recent devices is the small surveying device "LRTK" that can be used with a smartphone. LRTK realizes centimeter-level high-precision positioning via GNSS (Global Navigation Satellite System) (cm level accuracy, half-inch accuracy) in a palm-sized device and can be operated easily through a smartphone app even by beginners. With it, designers themselves can measure coordinates and elevations at site points or digitally record site elevation differences and area on the spot. This saves time and cost of hiring specialists and allows high-accuracy as-built data to be used for preliminary design even in small projects. Furthermore, LRTK makes it easy to share acquired data in the cloud and to integrate with other software for 3D modeling. This allows professionals from different disciplines to consider plans using the same up-to-date data, reducing misunderstandings and rework. LRTK has actually been adopted by municipalities and construction companies and is helping rapid situation assessment at disaster sites and simplifying surveys for small-scale works. The use of digital tools and simple surveying has become a powerful asset for carrying out accurate preliminary design efficiently with limited personnel.

Conclusion

The importance of robust preliminary design as the key to project success should be clear from these field-specific case studies. Although the fields differ—architecture, civil engineering, equipment, and urban development—common efforts such as early information gathering, flexible plan revision, and meticulous coordination among stakeholders are the driving forces that put plans on track. With advances in digital technologies, the accuracy and speed of preliminary design have dramatically improved. Including tools like LRTK discussed in this article, actively using available technologies while combining them with accumulated practical knowledge will make more reliable and persuasive project proposals possible. Please incorporate the key points from these success stories and apply creative, thoughtful preliminary design at your sites. Mastering this step, which greatly influences the future of a project, should lead to the next success story. For the intended readers of this article—small- and medium-sized design offices, general contractor design departments, and administrative staff—improving preliminary design capability brings significant benefits. For design offices, proposing optimal solutions within budget earns client trust and strengthens competitiveness for commissions. For general contractor design departments, it leads to reduced rework in construction and enriched VE proposals, improving project-wide efficiency. For administrative bodies, presenting accurate preliminary estimates early increases transparency of budget execution and smooths resident explanations and legislative approvals. Finally, preliminary design is the first step toward project success. Use the insights from this article to challenge yourself to produce high-quality preliminary designs. That accumulation will generate the next successful case.