Advantages and Disadvantages of Preliminary Design: Key Benefits and Challenges to Know

In the early stages of construction and civil engineering projects, a “preliminary design” is conducted to produce rough plans and cost estimates before detailed drawings and specifications are available. Preliminary design is a method of creating a project’s overview plan while estimating the approximate quantities and budget required. Specifically, it establishes basic design policies and structural schemes, and performs a preliminary quantity takeoff (preliminary estimate) based on information available at the time. These tasks are indispensable for grasping the overall scope and cost sense of a project early on, and for determining feasibility and securing budgets.

This article begins with the definition and purpose of preliminary design, then explains five advantages and five disadvantages. It also introduces situations where preliminary design is especially useful, precautions for carrying it out, recent technological trends and countermeasures. Finally, it touches on LRTK’s “簡易測量” feature as a new tool supporting preliminary design, exploring practical points that help in the field.

Definition and Purpose of Preliminary Design

Preliminary design refers to the rough design work carried out before entering detailed design (final design). In public works it is sometimes called “preparatory design,” and in private projects the early-stage schematic design corresponds to this. The purpose is to outline the project’s basic plan while estimating approximate construction costs and required material quantities to reflect them in the budget plan. For example, for roads or land development work, the preliminary design stage sets route options and development plans, and performs rough earthwork volume calculations to estimate approximate earthwork quantities and construction costs. For buildings, the building’s scale (gross floor area, number of floors, etc.) and structural specifications are decided, and preliminary construction costs are calculated based on data from similar projects and unit prices.

One major role of preliminary design is securing and adjusting budgets. The owner (client) uses the preliminary cost information obtained at this stage to judge whether the budget to be invested in the project is roughly appropriate. If the preliminary estimate indicates construction costs will exceed the budget, decisions such as downsizing the plan, revising specifications, or obtaining additional funds can be considered at this stage. When multiple plan options exist, comparing each preliminary construction cost makes it possible to evaluate cost aspects. In this way, preliminary design provides important data for decision-making that determines the project’s direction.

Furthermore, preliminary design is useful for scheduling and risk management. For example, identifying topography and environmental conditions early can reduce the risk of major design changes later. By identifying elements that affect project execution—such as ground conditions, property boundaries, and surrounding infrastructure—at the preliminary design stage, issues to be addressed in subsequent detailed design become clear. Such preparation makes it easier to forecast the overall project and proceed to the next step with a shared understanding among stakeholders.

Advantages of Preliminary Design (5 Benefits)

The benefits of performing preliminary design include the following.

• Faster plan formulation – Preliminary design can be completed in a shorter time than detailed design. Because the overall design can progress with limited information, it is possible to quickly indicate direction at the project initiation stage. Presenting an outline rapidly accelerates initial consultations with the owner and stakeholders and can move the whole project’s start date forward.

• Lower initial costs – By omitting detailed drawings and elaborate structural calculations, the time and expense associated with design work are reduced. Summarizing a preliminary design in a short period saves labor and outsourcing costs. In addition, the project as a whole can avoid unnecessary detailed design or excessive quality, enabling cost-conscious planning from the outset.

• Alignment with budget planning – Preliminary design provides an early preliminary estimate (preliminary quantity takeoff), making it easier to check consistency between the owner’s budget and the plan. If construction costs are likely to exceed the budget at the preliminary stage, it is possible to downsize the plan or revise specifications at that point. This prevents situations where the plan must be scrapped due to budget overruns after detailed design is completed. The ability to control costs early in the project is a significant advantage.

• Flexibility for plan changes – Because details are not finalized at the preliminary level, the design can flexibly accommodate plan changes. For example, when comparing option A and option B with different structural types or scales, preliminary design allows multiple plan patterns to be developed in a short time. Revision work due to changes is simple, so requests from the client or changes due to external factors can be responded to quickly. This flexibility is a major strength in dealing with early-stage project uncertainties.

• Early identification of risk factors – A bird’s-eye view of the project through preliminary design enables early detection of potential risk factors. For example, if construction challenges related to topography or ground conditions (such as the need for additional measures for soft ground or retaining walls to prevent collapse) are recognized at the preliminary stage, the plan can be revised to include contingency costs. Confirming regulatory issues and coordination points with the surrounding environment early on also reduces the risk of major design changes later. Preliminary design acts like a “trial run” of the project, surfacing hidden issues in advance.

Disadvantages of Preliminary Design (5 Challenges)

On the other hand, there are disadvantages and challenges of preliminary design that should be noted.

• Limits to design accuracy – Since detailed analysis and study are omitted at the preliminary stage, design accuracy is inevitably lower. Structural dimensions and quantity calculations are approximate, and many parts will require changes and adjustments during later detailed design. The plans produced at the preliminary design stage are only reference values and are not final. Errors due to rough accuracy are unavoidable, and this must be taken into account.

• Risk of errors in preliminary estimates – Construction cost and quantity estimates made at the preliminary stage carry uncertainty. Because the takeoff is based on limited information, there is a risk of deviation from the actual budget during construction. For instance, when estimating earthwork quantities preliminarily, if the ground hardness or groundwater conditions are not fully considered, additional excavation and treatment costs may arise later. Taking preliminary estimates at face value can lead to budget overruns, so it is important to be aware of the potential range of error.

• Rework during detailed design – Gaps frequently occur between preliminary design and actual detailed design, and filling these gaps can be time-consuming. Items handled with simplifications or assumptions at the preliminary stage may need to be reexamined from scratch in detailed design. In some cases, the preliminary plan may be technically unfeasible, requiring major changes to the structural scheme and replanning. Such rework leads to schedule extensions and additional costs, so preliminary planning must be read with the assumption that “further verification and revision will definitely be required later.”

• Oversights due to insufficient understanding of conditions – Preliminary design often proceeds based on limited survey data, and it may be necessary to advance the plan without fully grasping site topography or surrounding conditions. As a result, important requirements may be overlooked. For example, unmeasured areas may later reveal unexpected terrain obstacles, or coordination issues with agencies (permit conditions or infrastructure requirements) that were not anticipated may necessitate additional measures. Lack of initial information increases planning uncertainty, so at the preliminary design stage it is essential to clearly state unknowns and assumptions and plan follow-up measures accordingly.

• Perception gaps among stakeholders – Differences in understanding of the preliminary design can lead to disputes. For owners and project stakeholders, even preliminary plans or figures once presented are often perceived as “promised” values. Therefore, if costs increase or design changes occur later, it may cause dissatisfaction or confusion with comments like “that’s not what we were told.” The inherent uncertainty of preliminary design must be sufficiently shared; otherwise, the gap between expectations and reality becomes problematic. Ensuring all stakeholders correctly understand the nature of preliminary estimates is essential, but managing these expectations is itself an operational challenge.

Situations Where Preliminary Design Is Useful

Preliminary design is used in various situations in the construction and civil engineering fields. The main scenes include the following.

• Project planning stage: During the initial planning of a new project, preliminary design is conducted as material for assessing feasibility. For example, when a municipality plans infrastructure, multiple preliminary designs and estimated construction costs are compared to decide whether to adopt a project. In the private sector, preliminary design cost estimates are used in early-stage feasibility studies to calculate return on investment for development projects.

• Budget requests and financing plans: In public works, preparatory design (preliminary design) is essential for annual budget requests. Preliminary quantities and costs are calculated and used to determine the required budget amount to be submitted. In private companies, preliminary design estimates are used to secure internal project budgets, providing management and investors with an approximate funding requirement.

• Evaluation of design and construction methods: In procurement methods such as design-build or construction management, contractors may present preliminary designs and preliminary estimates early on. This allows the owner to select procurement methods and construction partners with an understanding of costs. Multiple contractors may be asked for preliminary proposals, and proposals and preliminary costs compared to choose the best option.

• Comparison of construction methods and alternatives: Preliminary design is also effective for technical evaluations. For example, when deciding between shield tunneling and cut-and-cover methods, each method’s preliminary design can be attempted to compare construction cost and schedule differences. Similarly, when choosing between reinforced concrete and steel frame for a building, both structural options can be evaluated at the preliminary stage and their preliminary takeoffs compared to assess cost and constructability advantages.

• Renovation and retrofit planning: For existing facility renovations or seismic upgrades, preliminary design is used to estimate rough work content and cost before starting. By surveying current conditions and designing the necessary renovation scope and methods at a schematic level, the approximate budget for renovation work can be understood. This helps determine whether to renovate or rebuild and to prioritize work items.

As shown above, preliminary design is widely used in decision-making scenarios such as early project judgments and plan comparisons. It is a method for assembling the most reliable information possible at the planning stage to identify the optimal option.

Precautions When Conducting Preliminary Design

To maximize the benefits of preliminary design while avoiding troubles from its disadvantages, the following points are important in practice.

• Sufficient site surveys and information gathering: Surveys tend to be limited by time and budget, but conduct field surveys, geotechnical investigations, and hearings with relevant agencies as much as possible. Accurately understanding topography and ground conditions improves the accuracy of quantity calculations (e.g., earthwork volumes and structural quantities) and reduces the risk of oversights.

• Plan for contingencies in estimated errors: Because uncertainty is high at the preliminary stage, include some contingency in the calculated quantities and costs. Specifically, add risk contingency to the preliminary estimate or apply safety factors to quantities. Including this contingency in the final budget helps suppress later requests for increased funding.

• Clarify assumptions: When presenting preliminary design documents or estimates to stakeholders, clearly state current assumptions and premises. For example, indicate “ground conditions estimated from past data,” “unit prices based on current market rates,” or “design loads assumed as X.” This allows recipients to understand the basis of the figures, making it easier to explain any differences that arise later.

• Provide careful explanations to stakeholders: Share with the owner and project team that plans and costs obtained at the preliminary design stage are provisional. Communicate that “changes are possible as details are developed” to appropriately manage expectations. Especially in terms of budget, preliminary figures are often perceived as a cap, so discuss planned stepwise reviews and the potential for additional funding as needed.

• Update design and maintain coordination: Treat plans created in preliminary design as living documents to be updated as detailed design progresses. When transitioning to basic design and final design phases, identify differences from the preliminary stage and reexamine costs and quantities. Close coordination between design and costing teams within the organization reduces discrepancies and smooths the transition from preliminary to implementation stages.

Recent Trends and Countermeasures in Preliminary Design

In recent years, advances in digital technology have improved the accuracy and efficiency of preliminary design. Preliminary estimates that once relied heavily on experience and past cases can now be derived more objectively and rapidly using the latest tools and software. Below are current trends surrounding preliminary design and the countermeasures they enable.

• Use of ICT and digital surveying: ICT technologies are being used in field surveying, such as drone aerial photogrammetry and 3D laser scanning for topographic measurement. These methods can acquire detailed terrain and point cloud data in a short time, dramatically improving the accuracy of site condition understanding that was previously unclear. For example, even for extensive development sites, drone surveys can rapidly calculate elevation differences and soil volumes, enabling more accurate volume calculations and quantity takeoffs at the preliminary design stage. This reduces early-stage errors and risks.

• Adoption of design support software and BIM: Design software for architecture and civil engineering has evolved, and functions that automatically extract quantities and calculate costs at the preliminary level are increasing. Using BIM (Building Information Modeling) or CIM (Construction Information Modeling) allows immediate extraction of material quantities from a 3D model and rough cost simulation. AI-powered estimating systems that learn costs from vast historical data of similar cases are also being trialed to improve the accuracy of preliminary estimates. Digital tools complement the designer’s intuition and experience, helping produce more reliable results in less time.

• Cloud-based collaboration and data sharing: Cloud sharing of design drawings and estimating documents is becoming common. This enables real-time information sharing and collaborative work among project stakeholders from the preliminary design stage. For example, if a designer uploads field survey data or preliminary takeoff results to the cloud, office-based team members can instantly check them. Change histories and comments can be exchanged online, making it easier for the whole team to refine plans. Eliminating information transmission lag and aligning stakeholder understanding make cloud technology a powerful countermeasure.

In addition to these technologies, smartphone-based easy surveying and measurement tools have emerged. For instance, LRTK’s “簡易測量” feature allows rapid acquisition of necessary data on site without specialized equipment. Using a small device attached to a smartphone and a dedicated app, anyone can easily measure high-accuracy position coordinates and perform photo positioning (photogrammetry) and coordinate recording on the spot. Acquired data is cloud synced with one tap and can be shared immediately with the office team. Furthermore, monopod measurement using a dedicated monopod enables stable surveying by a single person, making it smooth to measure distances between survey points and elevation differences. These features allow rapid topographic understanding and quantity checks on site and even enable rough soil volume (volume calculation) to be performed there, dramatically improving the accuracy and speed of preliminary design.

For example, ground elevation and site measurement data that used to require a surveying team and several days to obtain can be acquired in a short time using LRTK’s simple surveying tool. As a result, designers can check figures in the field while examining plans and immediately reflect them in the plan. By using photo positioning, it is possible to derive distances and areas from site photos and estimate necessary cross-section earth volumes from obtained point cloud data. Cloud-synced data eliminates the need to整理 data after returning to the office and enables same-day reflection into preliminary estimates and plan drawings. Thus, LRTK’s simple surveying function strongly supports achieving both speed and accuracy in preliminary design.

Conclusion

Preliminary design is a critical process that holds the key to project success. By correctly understanding its advantages and disadvantages and using it appropriately, you can improve decision-making accuracy in the early stages of a project and reduce waste and risk in later phases. This requires not only relying on experience and know-how but also actively adopting the latest technologies and tools. Digital surveying tools, cloud services, and solutions like LRTK’s 簡易測量 introduced in this article can compensate for the weaknesses of preliminary design and maximize its effectiveness. Make use of these tools to practice smart preliminary design that balances speed and accuracy.