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

What Is Preliminary Design and Its Role: A Review of Basics

"Preliminary design and cost estimation" refers to the rough design and cost calculation carried out at the early stage of a project. In this phase, planners develop concepts and estimate approximate construction costs based on limited information. This stage is a critical step for guiding projects to success across fields such as architecture, civil engineering, mechanical/electrical/plumbing (MEP), and urban development. By grasping project scale, specifications, and budget range before moving on to detailed design (construction documentation), teams can evaluate feasibility and build consensus among stakeholders. The role of preliminary design is to set the overall direction of the project and prevent rework in later phases. If an accurate preliminary estimate can be prepared early, budget overruns and major design changes later on can be avoided. Recently, the construction industry has seen more cases where budget overruns at the bidding stage force plan revisions, making improved accuracy in upstream preliminary estimates more important than ever. Additionally, public works have increased in recent years where soaring material prices lead to failed bids (no bids) or bids that exceed the planned price, highlighting the need for higher accuracy in the preliminary stage and flexible design revisions. This is particularly a compass for small- and medium-sized design offices and general contractor design departments, helping them keep projects on schedule with limited resources. For projects involving government agencies, preliminary design documents often form the basis for budget approval and project viability decisions, so highly reliable preliminary design is required.

Success Story 1: Architecture (Structural Review from Timber to Reinforced Concrete due to Change of Use)

In a local government public facility plan, the project was initially assumed to be a single-story wooden building with a total floor area of approximately 1,200 m². Planning for a wooden structure aimed to shorten the construction schedule and reduce costs, but a change of use occurred during the planning phase. With the addition of a role as a regional disaster prevention hub, a structure with higher durability and fire resistance was required, and the design team suddenly began considering changing from timber to reinforced concrete (RC). However, switching to RC typically increases construction costs by about 1.5 times compared to timber. As expected, keeping the same scale and functions with RC would cause the estimated construction cost to far exceed the original budget. For example, while the preliminary estimate for the timber scheme was about ¥200 million, changing to RC of the same scale was estimated at over ¥300 million, greatly exceeding the budget (about ¥220 million). The designers and cost managers therefore returned to the basic planning stage and began design revisions to absorb the cost increase from the structural change. Concretely, they reduced low-necessity ancillary spaces to compress the total floor area to about 1,100 m² and reorganized the structural design into a simple grid layout. They also avoided overly expensive finish materials and revised specifications to balance cost while ensuring durability. By repeatedly aligning plans and costs during the preliminary design stage, they succeeded in keeping the total preliminary construction cost for the RC option within the original budget (within roughly +5%). Early, flexible redesign and continuous updating of cost estimates enabled the team to finalize a plan acceptable to all stakeholders. Additionally, changing the structure to RC improved seismic resistance and durability, meeting the new usage requirements. This project is a good example of the importance of meticulous cost assessment and adjustments in preliminary design.

Success Story 2: Civil Engineering (Route Revision at the Preliminary Design Stage in a Road Improvement Project)

In a local road improvement project, it was discovered that the initial planned alignment did not adequately consider the site’s topography. On the plans, the shortest route was drawn as a straight line, but during the preliminary design phase detailed field survey data revealed a small valley along the route where water concentrates in heavy rain. Proceeding with construction as-is would have required massive fill and large drainage structures (such as box culverts) later, risking cost escalation and schedule delays. The design team revised the plan at the preliminary design stage to reflect topography and drainage planning. Specifically, they shifted the alignment to follow a gentle ridge avoiding the problematic valley, reducing height differentials and thereby cutting down on large-scale earthworks. At the same time, they incorporated the necessary drainage facilities (side ditches and drainage channels) into the design early on and created a preliminary estimate that included simulated stormwater flow paths and appropriately sized drainage structures. This route change and drainage plan review significantly reduced earthwork volume, producing an estimated cost saving of several tens of millions of yen on the preliminary estimate. As a result, the preliminary estimate could include drainage countermeasure costs that had originally been overlooked, avoiding later requests for additional budget. Subsequent detailed design required minimal changes, local coordination proceeded smoothly, and reflecting topographic conditions and drainage planning in the preliminary stage reduced overall project risk and enabled smooth construction. Furthermore, this improvement lowered the risk of drainage problems along the corridor, making it a desirable revision from environmental and disaster-prevention perspectives.

Success Story 3: MEP (Reuse Assessment and Construction Method Innovation in Pump Station Renewal)

A renewal project for aging urban infrastructure involved the refurbishment of a deteriorated drainage pump station. When modernizing a pump station decades old, the initial plan considered full demolition and rebuilding a new pump station from scratch. However, a preliminary estimate showed that demolition and new construction costs would far exceed the budget. There was also concern that the drainage function could not be stopped for a long time, making the cost of temporary pumping installations during construction a significant factor. Therefore, at the preliminary design stage the team conducted a detailed survey of the existing pump station. Inspection of the structural frame and piping systems found that some concrete tanks and foundations could be reused with reinforcement. Considering the layout and space of the existing pumps, they studied a construction method that would phase equipment renewal while retaining part of the existing building. Specifically, they planned a temporary structure allowing old and new pumps to be installed in parallel and to be switched over sequentially, minimizing pump downtime. As a result, by opting for a refurbishment plan that utilized existing assets instead of full replacement, they were able to significantly reduce the preliminary construction cost compared to the original scheme. Ultimately, about a 30% cost reduction at the preliminary stage was achieved, and the cost of temporary equipment was included in the estimate in advance to prevent additional later expenses. Thanks to prior investigation and construction method innovation, the aging facility was updated within budget while minimizing impacts on citizens’ daily lives. Reusing existing structures also reduced waste generation and contributed to lowering environmental impact.

Success Story 4: Urban Development (Initial Preliminary Estimate Including Land and Infrastructure Costs in a Redevelopment Project)

This is a case in an urban redevelopment project. A plan was launched to redevelop an aging building cluster in a station-front district into a mixed-use building with commercial facilities and residences. While the building construction cost itself was enormous, land acquisition costs and surrounding infrastructure development costs were even more critical to the project’s viability. For example, land acquisition costs in this area were estimated to be over ¥12 billion compared to building construction costs (assumed ¥10 billion), accounting for more than half of the total project cost. If these costs were not accurately incorporated into the initial preliminary design, later shortfalls in land acquisition or road improvement budgets could derail the entire project. Therefore, the developer and administrative departments leading the project conducted a detailed initial cost aggregation from the planning stage. Specifically, they investigated demolition costs to clear sites, compensation for relocation, and acquisition costs for dozens of land parcels, reflecting these early in the total project cost. They also coordinated with related authorities to estimate costs for new roads, water and sewage, and electrical infrastructure and included those in the preliminary estimate. Because these costs have greater uncertainty than building construction costs, contingency funds for risks were also included in the initial estimate. Thanks to this comprehensive preliminary design, although the total project cost rose above initial assumptions, obtaining realistic figures early allowed rapid revision of financing plans and business schemes. Consequently, flexible responses such as securing additional funding or phasing the project became possible, and the project has proceeded without major trouble. Presenting realistic numbers from the outset also helped build trust with local residents and investors, smoothing procedures. This case demonstrates that in urban development, including land acquisition and infrastructure costs from the initial stage of preliminary design is a critical factor determining project success.

Common Measures and Checkpoints Across the Cases

From the above cases, we can distill common measures and checkpoints for the preliminary design stage:

• Thorough site investigation and information gathering at an early stage: Understanding the actual site conditions and the state of existing assets at the project’s outset reduces unforeseen issues later. It is important to identify topography, building conditions, and applicable regulations early.

• Consideration of cost-conscious alternatives: Compare multiple plans paired with preliminary estimates and seek options with better cost performance. If necessary, propose alternatives such as reducing scale or changing specifications without hesitation.

• Close communication with stakeholders: Hold repeated meetings with owners and relevant agencies from the early stage to share goals and constraints. If signs of budget overruns appear, report early and discuss countermeasures to facilitate consensus.

• Identification of risk factors and inclusion of contingencies: Identify uncertainties and potential risks and reflect them in the preliminary estimate. Consider often-overlooked costs such as land acquisition and temporary works, as well as price fluctuation risks, and set contingency funds with sufficient margin.

• Utilization of specialist knowledge and digital tools: When needed, draw on the expertise of cost engineers and structural specialists and use the latest tools for higher-accuracy data collection and simulation. This further enhances the reliability of preliminary design.

Use of Digital Tools and Simple Surveying

In recent years, digital transformation (DX) has swept through the construction and design fields, and preliminary design can also benefit from it. In particular, the use of modern digital tools and simple surveying devices for site assessment and quantity takeoff has attracted attention. For example, terrain surveying that traditionally required a professional surveyor can now produce detailed terrain models quickly using aerial photogrammetry with small drones or point cloud measurement with 3D laser scanners. For building interior renovation planning, 360-degree cameras and smartphone-linked laser distance meters enable immediate capture of as-built dimensions, and such cases are increasingly useful for initial planning. Design software advances are also streamlining preliminary-stage work. For instance, BIM (Building Information Modeling) can automatically extract quantities from an initial model and quickly generate preliminary estimates. AI-based estimating tools that leverage past project data are also emerging, enabling designers to refine plans while monitoring costs in real time. One recently introduced device is the compact surveying tool "LRTK," usable with a smartphone. LRTK provides centimeter-level high-precision positioning via GNSS (Global Navigation Satellite System) in a handheld form factor and can be operated easily by beginners through a smartphone app. With this, designers themselves can measure coordinates and elevations at site points or digitally record site elevation differences and area on the spot. It saves the time and cost of hiring specialist contractors and allows accurate as-built data to be used for preliminary design even in small projects. Moreover, LRTK makes it easy to share acquired data in the cloud or link it with other software for 3D modeling. This enables engineers from different fields to work from a common, up-to-date dataset, reducing miscommunication and rework. LRTK has been adopted by municipalities and construction companies for rapid disaster site assessments and simplified surveying for small projects. The use of digital tools and simple surveying has become a powerful asset for conducting accurate preliminary design efficiently with limited personnel.

Conclusion

The importance of robust preliminary design as a key to project success should be clear from these cases. Regardless of whether the field is architecture, civil engineering, MEP, or urban development, early information gathering, flexible plan revisions, and meticulous coordination among stakeholders are common practices that drive projects onto a successful track. With recent digital advances, the accuracy and speed of preliminary design have improved dramatically. By actively using available tools such as LRTK while combining them with traditional experience and know-how, more reliable and persuasive project proposals become possible. Consider the points from the success stories presented here and apply creative approaches to preliminary design at your sites. Mastering this step, which profoundly affects a project’s future, will help generate the next success stories. For the article’s intended readers—small and medium-sized design offices, general contractor design departments, and administrative staff—improving preliminary design capability brings great benefits. Design offices can gain clients’ trust by proposing optimal solutions within budget, enhancing competitiveness. For general contractors’ design divisions, it reduces rework during construction and enriches value engineering proposals, improving overall project efficiency. For administrators, presenting accurate preliminary estimates in the early stage increases transparency in budget execution and facilitates resident briefings and council approvals. Finally, preliminary design is the first step toward project success. Use the insights shared here to take on high-quality preliminary design. Those cumulative efforts will produce future success stories.