Advantages and Disadvantages of Preliminary Design: Key Benefits and Challenges

In the early stages of construction and civil engineering projects, a "preliminary design"—which estimates a rough plan and costs before detailed drawings and specifications are available—is carried out. Preliminary design refers to a method of creating a project's outline plan while estimating the approximate quantities and budget required. Specifically, it involves determining basic design policies and structural forms, and performing preliminary quantity takeoffs (preliminary estimates) based on information available at that time. These activities are essential for understanding the project's overall scope and cost early on, and for deciding feasibility and securing a budget.

This article begins by defining the purpose of preliminary design, then explains five advantages and five disadvantages. It also describes scenarios where preliminary design is useful, points to watch when conducting it, recent technological trends and countermeasures, and finally touches on LRTK’s "Simple Survey" feature as a new tool that supports preliminary design, highlighting practical points for field use.

Definition and Purpose of Preliminary Design

Preliminary design is the rough design work carried out before entering detailed design (construction design). In public works it is sometimes called "preliminary design," and in private projects the schematic design conducted at the planning stage corresponds to this. The purpose is to draft the project's basic plan while estimating approximate construction costs and material quantities to reflect in the budget plan. For example, in road or land development projects, preliminary design establishes route options and development plans, and estimates rough earthwork quantities and construction costs by calculating cut-and-fill volumes. For buildings, it determines building scale (gross floor area, number of stories, etc.) and structural specifications, and calculates preliminary construction costs using data and unit prices from similar projects.

One major role of preliminary design is budget securing and adjustment. Owners (clients) use the preliminary cost information obtained at this stage to judge whether the project's budget is roughly reasonable. If preliminary estimates indicate costs may exceed the budget, the plan can be scaled down or specifications revised at this point, or additional budget sought. When multiple plan options exist, comparing each option’s preliminary construction cost enables cost-based consideration. In this way, preliminary design provides important data for decision-making on project direction.

Preliminary design also helps with scheduling and risk management. For example, early recognition of topography and environmental conditions can reduce the risk of major design changes later. By identifying factors that may affect project execution—such as ground conditions, property boundaries, and surrounding infrastructure—during the preliminary design stage, issues to be addressed in subsequent detailed design can be clarified. This preparation improves overall project visibility and allows stakeholders to proceed to the next step with a shared understanding.

Advantages of Preliminary Design (5 Benefits)

The following are benefits gained by conducting preliminary design.

• Faster plan formulation – Preliminary design can be completed in a shorter period than detailed design. Because it advances the outline with limited information, it is possible to quickly indicate project direction at the project's startup. Presenting an outline quickly accelerates initial consultations with the owner and stakeholders, allowing the overall start to be moved forward.

• Lower initial costs – By omitting detailed drawings and extensive structural calculations, you can reduce the effort and cost of design work. Completing a schematic design in a short time saves labor and outsourcing costs. At the project level, avoiding unnecessary detailed design or over-specification enables planning with cost awareness from the outset.

• Alignment with budget planning – Preliminary design provides an early preliminary estimate (quantity takeoff), making it easier to check alignment between the owner's budget and the plan. If the preliminary estimate suggests costs will exceed the budget, decisions such as scaling down the plan or revising specifications can be made then. This prevents situations where a plan must be scrapped after detailed design due to budget overruns. The ability to control costs early in the project is a major advantage.

• Flexibility for plan changes – At the preliminary level, because design details are not finalized, plans can be changed flexibly. For example, when comparing Plan A and Plan B with different structural forms or scales, preliminary design allows multiple patterns to be created in a short time. Corrections required by changes are simple, so changes in client requirements or adjustments due to external factors can be addressed quickly. This flexibility is a significant strength in dealing with uncertainty in the early stages of a project.

• Early detection of risk factors – By taking an overall view of the project during preliminary design, potential risk factors can be identified early. For instance, if construction issues related to topography or ground conditions (such as the need for ground improvement or additional retaining walls to prevent collapse) are recognized at the preliminary stage, the plan can be revised to include countermeasure costs. Also, checking regulatory requirements and coordination with the surrounding environment early can reduce the risk of major design changes later. Preliminary design acts like a "trial run" for the project, surfacing latent issues in advance.

Disadvantages of Preliminary Design (5 Challenges)

On the other hand, there are drawbacks and challenges to be aware of with preliminary design.

• Limitations in design accuracy – Because detailed analyses and examinations are omitted at the preliminary stage, design accuracy is inevitably lower. Structural dimensions and quantity calculations are approximate, and many items will require changes or adjustments during detailed design. Plans compiled at the preliminary design stage are only reference values, not final. Errors due to low precision are unavoidable and must be acknowledged.

• Risk of errors in preliminary estimates – Preliminary costs and quantities come with uncertainty. Because takeoffs are based on limited information, there is a risk of divergence from the actual budget during construction. For example, if the ground hardness or groundwater conditions are not adequately considered when approximating earthwork quantities, additional excavation or treatment costs may arise later. Blindly trusting preliminary estimates can lead to budget overruns, so it is important to be aware of the potential margin of error.

• Rework during detailed design – There is often a gap between preliminary design and actual detailed design, and filling that gap can be labor-intensive. Parts that were simplified or handled with assumptions at the preliminary stage may need to be re-evaluated from scratch during detailed design. In some cases, plans from the preliminary stage may be technically infeasible and require major changes in structural form—i.e., reworking the plan. Such rework can extend schedules and increase costs, so it is necessary to plan on the premise that detailed verification and revision will inevitably occur later.

• Oversights due to insufficient condition understanding – Preliminary designs are often based on limited survey data, meaning projects sometimes proceed without fully grasping site topography or surrounding conditions. As a result, important requirements may be overlooked. For example, an unmapped area might later reveal unforeseen topographic obstacles, or negotiations with related authorities (permit conditions, infrastructure requirements, etc.) might be overlooked, requiring additional countermeasures. Insufficient initial information increases uncertainty, so the preliminary design stage should clearly state unknowns and assumptions and plan follow-up measures accordingly.

• Recognition gaps among stakeholders – Differences in how stakeholders perceive the preliminary design can cause trouble. Owners and project participants tend to interpret a presented plan or figure—even if only preliminary—as if it were a "promise." If costs increase or design changes occur later, it can lead to complaints or confusion that "the situation is different." Although preliminary design outputs inherently contain uncertainty, failing to share that fact adequately can result in a gap between expectations and reality. Ensuring all stakeholders correctly understand the nature of preliminary estimates is essential, but managing those expectations is itself a practical challenge.

Situations Where Preliminary Design Is Useful

Preliminary design is used in many contexts within construction and civil engineering. The main scenarios include the following.

• Project planning stage: During initial project planning, preliminary design is conducted as material for feasibility assessment. For example, when a municipality plans infrastructure improvements, it compares multiple preliminary designs and estimated construction costs to decide whether to adopt the project. In the private sector, preliminary design-based cost estimates are used in early investment evaluations for development projects.

• Budget requests and financial planning: For public projects, preliminary design (schematic design) is required for annual budget requests. Preliminary quantities and costs are calculated to determine the necessary budget amount for submission. In private companies, preliminary estimates are used to secure internal project budgets, giving management or investors an approximate idea of required funding.

• Evaluation of procurement and construction methods: In design-build or construction management procurement methods, contractors may submit preliminary designs and estimates early. This allows the owner to grasp costs when selecting procurement methods or construction partners. Multiple contractors may be asked for preliminary proposals, and decisions are made by comparing proposals and estimated costs.

• Comparison of construction methods and alternatives: Preliminary design is also useful for technical evaluations. For example, when deciding between tunneling with a TBM (tunnel boring machine) or cut-and-cover methods, preliminary designs for each can be attempted to compare costs and construction time. Similarly, when choosing between reinforced concrete and steel framing for a building, both structural options can be evaluated at the preliminary stage and compared via preliminary quantity takeoffs to assess cost and constructability.

• Renovation and retrofit planning: For renovations or seismic retrofits of existing facilities, preliminary design is used to estimate the rough scope and cost before starting work. By surveying the current conditions and developing a schematic plan of required repairs and methods, the budget scale for the retrofit can be grasped. This helps decide whether to renovate or rebuild, and to prioritize work.

As shown above, preliminary design plays a broad role in early project decisions and plan comparisons, helping decision-making. It is a method for assembling the most reliable information possible at the planning stage to identify the best options.

Points to Note When Conducting Preliminary Design

To maximize the benefits of preliminary design and avoid troubles from its disadvantages, the following practical points should be observed.

• Sufficient site investigation and information gathering: Although time and budget constraints often limit surveys, conduct site surveys, geotechnical investigations, and hearings with relevant authorities to the greatest extent 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 with allowance for errors: Since uncertainty is high at the preliminary stage, include some contingency for the calculated quantities and construction 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 claims for additional funds.

• Clarify assumptions and conditions: When presenting preliminary design documents or estimates to stakeholders, clearly state current assumptions and provisional conditions. For example, indicate if "ground conditions are estimated from past data," "unit prices refer to current market rates," or "design loads assume X." This helps recipients understand the basis for the figures and makes it easier to explain differences if they arise.

• Careful explanation to stakeholders: Share with the owner and project members that plans and costs obtained at the preliminary stage are provisional. Communicate that "changes are possible with subsequent detailing" to appropriately manage expectations. In particular, since budgets are often perceived as "the upper limit" when presented as preliminary figures, discuss plans for staged reviews or potential additional funding as needed.

• Update designs and coordinate: Treat preliminary plans as items to be updated continuously as detailed design progresses. When transitioning to schematic or construction design phases, identify differences from the preliminary stage and reexamine costs and quantities. Close coordination between design and cost-estimating teams helps reduce discrepancies and smooth the transition from preliminary to implementation phases.

Recent Trends in Preliminary Design and Countermeasures

Recently, advances in digital technology have improved the accuracy and efficiency of preliminary design. Preliminary estimates, once heavily reliant on experience and past cases, can now be calculated more objectively and quickly using modern tools and software. Below are key trends and what they enable.

• Use of ICT and digital surveying: ICT technologies are playing an active role in field surveying, such as aerial photogrammetry using drones and topographic measurement with 3D laser scanners. These methods can collect detailed terrain and point cloud data in a short time, dramatically improving the accuracy of previously unclear site surveys. For example, drone surveys can quickly calculate elevation differences and earth volumes over large development sites, enabling more accurate volume calculations and quantity takeoffs during the preliminary design stage. This reduces initial planning errors and risks.

• Adoption of design support software and BIM: Design software for architecture and civil engineering has evolved to include functions that automatically extract quantities and support cost estimation even at the preliminary level. Using BIM (Building Information Modeling) or CIM (Construction Information Modeling), material quantities can be instantly derived from 3D models and rough cost simulations performed. AI-assisted estimating systems that learn costs from large datasets of past projects are also being trialed to improve the accuracy of preliminary estimates. Digital tools complement designers’ intuition and experience, helping produce more reliable results quickly.

• Collaboration and data sharing via the cloud: Cloud sharing of design drawings and estimating documents is becoming common. This enables real-time information sharing and collaboration among project stakeholders from the preliminary design stage. For example, when a designer uploads site survey data or preliminary takeoff results to the cloud, office team members can immediately review them. Online change histories and comments make it easier for teams to refine plans together. Eliminating information transmission delays and aligning stakeholder understanding makes cloud technology a powerful mitigation tool.

Alongside these trends, smartphone-based, easy-to-use surveying and measurement tools have also appeared. For instance, LRTK’s "Simple Survey" feature allows rapid on-site data acquisition without specialized instruments. By attaching a small device to a smartphone and using a dedicated app, anyone can easily measure high-accuracy position coordinates, perform photogrammetry (photo-based measurement), and record coordinates on the spot. Collected data can be synced to the cloud with a tap, enabling immediate sharing with office teams. Additionally, monopod measurement using a dedicated monopod permits stable surveying by a single person, facilitating distance and elevation measurements between points. These functions enable rapid on-site terrain assessment and quantity checks, even allowing approximate earthwork (volume calculation) on the spot, dramatically improving the speed and accuracy of preliminary design.

For example, where one would previously have needed to dispatch a survey team and spend days obtaining ground elevation and site measurement data, LRTK’s Simple Survey tool can acquire the same data in a short time. As a result, designers can check figures on site while refining plans and reflect them in the plan immediately. Using photogrammetry, you can derive distances and areas from site photos or estimate required cross-section earth volumes from point cloud data. Cloud-synced data reduce post-fieldwork整理 (reworking) in the office and allow same-day reflection in preliminary estimates and planning drawings. Thus, LRTK’s Simple Survey feature strongly supports both the speed and accuracy demanded of preliminary design.

Conclusion

Preliminary design is a crucial process that can determine a project’s success. By correctly understanding its advantages and disadvantages and using it appropriately, the accuracy of early project decisions can be improved and waste and risk in later stages reduced. This requires not only relying on experience but also actively incorporating the latest technologies and tools. Modern digital surveying tools, cloud services, and solutions like LRTK’s Simple Survey introduced in this article are powerful allies that compensate for the shortcomings of preliminary design and maximize its effectiveness. Use these tools to practice smart preliminary design that balances speed and accuracy.