Efficient Methods for Preliminary Design Estimation: Practical Steps and Key Points for the Field

Introduction

Successful building and civil engineering projects depend on conducting preliminary design estimation in the early planning stages. Preliminary design estimation is the process of creating a rough design plan and estimating the required construction costs based on limited information before detailed drawings and specifications are complete. Performing preliminary design early and verifying alignment between the design and the budget helps prevent major design changes and budget overruns later on.

Preliminary design estimation forms the foundation for a client’s budget planning and plays an important role for contractors and designers as part of cost control. For example, municipalities use preliminary cost estimates to request budgets, while private companies use them to assess project viability. For designers and engineers in the field, efficiently carrying out preliminary design and quickly presenting accurate preliminary estimates helps the project get off to a smooth start. This article explains the basics of “what preliminary design estimation is,” outlines an efficient workflow, presents practical field tips, and discusses operational considerations. Finally, we touch on ways to accelerate the initial stages of preliminary design using new technologies such as smartphone surveying.

What is preliminary design estimation? Basic concepts and purposes

Preliminary design estimation refers to the simplified design and preliminary cost estimation carried out at the early stage of a project. Concretely, it involves creating rough sketches or models based on the project overview (purpose, scale, specifications, site conditions, etc.), extracting approximate required quantities from these, and estimating construction costs. The goal is to grasp a rough plan and cost before detailed design and formal quantity takeoffs are completed.

There are two main purposes for using preliminary design estimation. One is budget management and cost planning. Clients use preliminary construction cost estimates to secure budgets, apply for financing, or seek grants. For designers, appropriate preliminary estimates enable early correction of mismatches between design and target budget, allowing the establishment of an efficient basic plan without waste. The other purpose is to support project decision-making. Preliminary design estimation makes it easier to determine whether a plan is feasible or which alternative is most economical. For example, when considering building size or structural types, comparing preliminary costs helps select the option with the best cost-effectiveness. Preliminary design estimation is therefore a key tool for setting the project direction early and establishing a common understanding among stakeholders.

How to proceed efficiently with preliminary design estimation: step-by-step (survey → sketch → quantities → unit prices → costing)

To carry out preliminary design estimation efficiently, it is important to divide the work into several steps and proceed in order. Below, we explain the main flow of preliminary design estimation in five steps.

• Site survey and information gathering (Survey): Start by understanding the site and planning conditions. Investigate the site shape, elevation differences, ground conditions, locations of existing infrastructure (roads, water/sewer, power, etc.), sunlight and surrounding environment, and regulatory constraints (zoning, building coverage ratio, floor area ratio, building restrictions). Conduct hearings and collect related documents at this stage to gather as accurate as possible the information that will form the assumptions for design. The higher the survey accuracy, the better the subsequent plan and cost estimation precision.

• Creation of a preliminary plan (Sketch): Next, develop a rough design plan (basic concept) based on the collected information. Draw rough sketches of plans and sections to determine the layout, scale, and structural form of facilities or structures. For buildings, draft room layouts and number of floors; for civil works, define routes and cross-sectional shapes—create a concrete overall image to the extent possible. At this stage, emphasize the overall picture and feasibility rather than details, and if multiple options exist, compare and evaluate preliminary plans to determine the direction.

• Estimation of approximate quantities (Quantities): Once the plan is set, calculate the main quantities based on that plan. For buildings, extract gross floor area and sizes/quantities of major elements; for civil works, calculate excavation or embankment volumes and lengths/areas of structures. You do not calculate detailed quantities as in final design, but it is important to understand approximate quantities by key work items and elements. Using drawings from past similar projects or standard cross-section models improves accuracy. Also incorporate assumptions for uncertain items (e.g., equipment capacities or the need for special works) into the estimate.

• Setting unit prices (Unit prices): After quantities are ready, assign unit prices for each item. A unit price is the price per unit of work or material; multiplying unit prices by quantities gives the costs. Reference market rates, past project records, and public construction pricing guidelines when setting unit prices. For example, in building preliminary estimates it is common to use composite unit prices such as “X work: Y amount per m²” or “equipment set: Z amount per unit.” Monitor current construction market prices and material trends, and adjust unit prices to account for price fluctuations when necessary.

• Costing the preliminary construction budget (Costing): Finally, multiply the set quantities by the unit prices to calculate the cost of each item, and sum these to produce the project’s overall preliminary construction cost. Provide breakdowns for major categories such as building structure costs, equipment costs, and civil works, and include design fees, management fees, and contingencies as needed. Check whether the calculated preliminary construction cost fits the initial budget or target cost; if it significantly exceeds them, return to the plan to adjust (e.g., consider VE options). In this way, complete the alignment of cost and design content at the preliminary design stage.

Following these steps allows you to conduct preliminary design estimation systematically. Clarifying the flow from survey to costing prevents omissions and streamlines the work.

Practical tips for the field: survey accuracy, on-site understanding techniques, and tools

To carry out preliminary design estimation smoothly and reliably in the field, apply several practical techniques and points. Here are tips that practitioners should keep in mind.

• Increase survey accuracy: Conduct thorough on-site surveys where possible to collect high-quality data. On site, measure site dimensions and elevation differences, verify ground investigation results and information on existing buried utilities. Conduct desk research using drawings or geographic information systems (GIS) before going to the site, then perform on-site measurements and confirmations—this is efficient. The more reliable the data obtained during the survey stage, the fewer reworks in later quantity takeoffs and planning, and the faster the preliminary design process will be.

• Techniques for understanding site conditions: Use photos, videos, and sketches in addition to textual information and drawings to build a three-dimensional understanding of site conditions. Grasping the surroundings (adjacent buildings, road conditions, delivery routes, etc.) helps avoid overlooking design constraints. Bringing a senior technician with experience is also effective, as they can point out potential issues (for example, “this ground may require foundation reinforcement”). Preparing a checklist is useful for efficient data collection when survey time is limited.

• Use of IT tools: Employing modern digital tools for on-site data collection and preliminary design work can greatly improve efficiency. For example, acquiring site topography data via drone aerial photos or simple laser scans makes it possible to review details later at the office. Creating preliminary models in BIM or CAD software automates area and volume calculations, reducing the work of quantity takeoffs. Using estimating software or spreadsheets to manage unit prices and quantities enables quick recalculation when changes occur. Today, there are tablet and smartphone apps that allow drawing review and dimension measurement, improving information flow between the field and the office. Actively adopt these tools to establish an environment for fast and accurate preliminary design estimation.

Operational considerations: risks of overestimation and underestimation, and handling design changes

When performing preliminary design estimation, be aware of several practical considerations—especially the risks of overestimation and underestimation and how to handle subsequent design changes.

First, the risks of overestimation and underestimation. Even at a preliminary stage, estimates that are far from reality are problematic. Underestimation (estimating costs too low) can lead to budget overruns being discovered later, jeopardizing project continuation or requiring major reductions. Conversely, overestimation (estimating costs too high) may present an unnecessarily large budget early on, causing the project to be rejected or forced to downscale. Preliminary estimates presented to clients are often treated as an “upper limit that must not be exceeded.” Therefore, it is important to present as realistic a preliminary construction cost as possible. While there is a natural desire to include safety margins, excessive inflation is not acceptable. Set appropriate risk margins (contingencies) for uncertain elements, but base calculations on quantities and unit prices with clear rationale. Explicitly stating the assumptions and specifications used in the estimate makes it easier to justify the estimate’s validity later.

Next, responding to design changes and ensuring coordination. Because the full project details are not fixed at the preliminary design stage, design changes and greater detail during schematic and detailed design phases are inevitable. What’s critical is having a mechanism to promptly review preliminary costs when design changes occur. Update the preliminary estimate as the project moves into schematic design, and evaluate the cost impacts of major changes (such as increases or decreases in gross floor area or specification changes) each time. Share the assumptions and conditions used in the preliminary estimate with the client and project stakeholders, and report and consult on how those assumptions change during revisions. Even when design and estimating personnel are separate, maintain close coordination to prevent information loss. If a budget limit was agreed upon during the preliminary stage and cost increases arise during detailed design, consider adjustments through alternatives (Value Engineering, VE) to keep the plan within budget. In short, since the plans and budget set during preliminary design serve as guiding references thereafter, continuous cost management to maintain consistency across project phases—despite changes—is essential.

Conclusion

Preliminary design estimation is a critical early-stage step, and the approach taken here can significantly influence the subsequent course of the project. Performing preliminary design at the appropriate time and confirming the balance between budget and design are key to steadily advancing the plan. This article covered the basic concepts of preliminary design estimation, an efficient workflow, practical field techniques, and important considerations. The key points are summarized below.

• Role of preliminary design estimation: Calculate the approximate design content and construction cost early in the project to form the basis of budget planning. Early preliminary estimates reduce the risk of budget overruns and help control design and costs.

• Efficient workflow: Follow the steps “survey → plan creation → quantity takeoff → unit price setting → costing” to perform comprehensive and smooth preliminary design estimation. Using appropriate methods and data at each stage improves accuracy.

• Field techniques: Accurately capture site conditions during the survey stage and harness IT tools to quickly gather necessary information. Use BIM/CAD and estimating software to streamline quantity takeoffs and estimating, and prepare to compare multiple options and respond flexibly to changes.

• Considerations: Avoid significant over- or underestimation by presenting realistic costs based on evidence. Share preliminary assumptions with stakeholders and promptly reflect design changes in cost estimates to continually align design and budget.

Carrying out reliable preliminary design estimation quickly helps the overall project progress smoothly. While experience and intuition still play a role, following systematic procedures and leveraging modern tools can greatly improve both the accuracy and speed of preliminary design estimation.

Finally: Accelerating the initial stages of preliminary design with smartphone surveying using LRTK

In recent years, digital technologies that enhance field productivity have emerged, enabling high-accuracy surveying by combining smartphones with dedicated devices. A prominent example is smartphone surveying using LRTK (high-precision RTK-GNSS positioning system). By using LRTK, you can obtain accurate surveying data on site in a short time with minimal equipment and personnel, dramatically accelerating the initial stages of preliminary design.

Traditionally, obtaining current survey maps and topographic data at the planning stage required commissioning a survey team and waiting for results. With LRTK, project staff can perform surveys themselves using a smartphone. For example, by attaching a compact GNSS receiver compatible with LRTK to a smartphone and walking the site, you can acquire coordinates of site boundaries and elevation data in real time. The horizontal positioning accuracy is very high—on the order of ±2 cm—and comparable to surveys performed with specialized equipment. Measured data can be saved and shared to the cloud immediately, so by the time you return to the office the whole team can already view the latest site data.

Using such smartphone surveying during the preliminary design phase drastically shortens the time required for site surveys and creation of survey maps. With on-the-spot knowledge of ground elevations and site dimensions, you can start drafting preliminary plans and performing quantity takeoffs immediately after surveying. LRTK systems often offer optional features such as simple 3D point cloud scanning and AR functions, enabling rough earthwork volume estimates from acquired point clouds or overlaying planned facilities on the smartphone screen for on-site verification. These capabilities are particularly powerful in the early phases of preliminary design.

By incorporating smartphone surveying with LRTK, anyone can easily digitize an accurate snapshot of the site and get a head start on preliminary design estimation. Because it improves both survey accuracy and time efficiency, this approach is a strong ally when high-quality planning is required within limited time. Make effective use of new technologies to carry out preliminary design estimation reliably and quickly. Try adopting them in your next project and experience the benefits for yourself.