The further a construction project progresses, the more concrete not only the planning and execution but also the expected costs must become. This is exactly where cost estimation comes into play. It translates the current state of planning into a structured cost analysis, thereby creating an important foundation for further planning, bidding, and cost control. <\/p>\n\n
For architects, engineers, and design firms, this involves much more than simply adding up individual cost items. Quantities must be determined with a high degree of reliability, building components and technical solutions must be taken into account, costs must be allocated correctly, and assumptions must be documented in a transparent manner. Inaccurate quantities, outdated parameters, or an inconsistent cost structure, on the other hand, can lead to deviations that only become apparent much later in the project. <\/p>\n\n
At NOVA AVA, we focus intensively on precisely these processes. In this article, we\u2019ll show you what goes into a cost estimate in the construction industry, how it fits into cost planning according to DIN 276 and HOAI<\/a>, and what you should pay special attention to when preparing one. <\/p>\n\n Cost calculation is a stage in the cost estimation process in the construction industry. It is prepared based on a design that has already been finalized and is intended to provide a much more detailed picture of the projected project costs than earlier cost estimates. <\/p>\n\n DIN 276 serves as a key foundation for this. The current edition, DIN 276:2018-12, \u201cCosts in Construction,\u201d describes, among other things, the systematic classification, determination, documentation, and control of project costs. The standard organizes costs into main and sub-cost groups, thereby establishing a uniform basis for cost planning. <\/p>\n\n During a cost estimate, the planning information\u2014which has now become more specific\u2014is linked to quantities and cost indicators or unit prices. The result is a much more detailed assessment of the expected costs of the planned structure. <\/p>\n\n The key point here is that a cost estimate is not a static document that is created once and then filed away. It is part of an ongoing cost planning process and serves as an important reference for later project phases. <\/p>\n\n In the scope of services for buildings and interiors, cost estimation is part of Service Phase 3\u2014Preliminary Design\u2014according to the HOAI.<\/p>\n\n The HOAI explicitly lists cost calculation in accordance with DIN 276 and a comparison with the previously prepared cost estimate as basic services for this phase.<\/p>\n\n This makes sense from a technical standpoint: During the preliminary planning phase, many decisions have not yet been finalized. By the design planning phase, the structure, materials, technical systems, dimensions, and other key planning parameters are already much more specific. <\/p>\n\n This also changes the basis for cost estimation. Instead of relying primarily on rough estimates, costs can increasingly be derived from the actual characteristics of the planned project. <\/p>\n\n This makes the cost calculation an important checkpoint: Does the finalized design still fit within the previously defined economic parameters?<\/p>\n\n DIN 276 establishes a standardized system for cost planning in the construction industry. Costs are not grouped arbitrarily but are assigned to a defined cost classification. The current version of DIN 276 comprises eight main cost groups at the first level of classification. <\/p>\n\n This overarching structure can be further subdivided. This allows costs to be recorded and analyzed in greater detail as planning progresses. <\/p>\n\n This is precisely where a key advantage lies: If costs are consistently categorized throughout the entire project, it becomes much easier to compare different cost figures with one another.<\/p>\n\n Cost calculations should therefore not be viewed in isolation. They build on previous findings and, in turn, form the basis for subsequent cost controls. <\/p>\n\n The quality of a cost estimate depends directly on the quality of the underlying planning.<\/p>\n\n During the preliminary design phase, key decisions regarding the structure have already been made. These include, for example, dimensions, floor areas, volumes, structural systems, materials, technical systems, and quality requirements. <\/p>\n\n Based on this information, quantities can be determined and assigned to the corresponding cost estimates.<\/p>\n\n A reliable cost estimate therefore requires, in particular, a sufficiently detailed proposal, quantities determined in a transparent manner, an appropriate cost breakdown, and reliable cost indicators or unit prices.<\/p>\n\n Equally important is the price level of the data used. Construction costs change over time and can vary by region. Historical comparative figures should therefore not be applied to a current project without verification. <\/p>\n\n Project-specific factors also play a role. A challenging lot, special technical requirements, high finishing standards, or complex construction processes may necessitate adjustments to seemingly appropriate comparables for the specific project. <\/p>\n\n A good cost estimate is not the result of a single formula. It is the result of a structured process that integrates planning, quantities, and cost rates. <\/p>\n\n The first question is: What is the basis for the calculation?<\/p>\n\n Have key components already been sized? Have materials and grades been defined? Are the specifications from the specialized design teams available? Are there still options that have not yet been decided upon? <\/p>\n\n The clearer these fundamentals are, the more reliable the cost calculation can be.<\/p>\n\n Any outstanding decisions should be documented. This ensures that it will be possible to trace later which assumptions a particular cost figure is based on. <\/p>\n\n In the next step, relevant quantities are determined from the planning data. These may include, for example, areas, volumes, quantities, or other appropriate reference quantities. <\/p>\n\n Quantity takeoff is one of the most important components of cost estimation. Errors have a direct impact on the calculated costs. <\/p>\n\n Particularly problematic are quantities that appear mathematically correct but no longer reflect the current status of planning. If a plan is changed without updating the corresponding cost estimate, the cost calculation quickly loses its significance. <\/p>\n\n The calculated costs are then allocated to an appropriate structure.<\/p>\n\n When calculating costs in accordance with DIN 276, this is done using the corresponding cost groups. This makes it possible to identify which costs are incurred in which areas of the project. <\/p>\n\n At the same time, the structure is crucial for future comparisons. Only when cost reports are organized according to a consistent system can one determine where costs have changed between different planning stages. <\/p>\n\n The quantities determined are then linked to appropriate cost factors or unit prices.<\/p>\n\n To this end, one can draw on, for example, current project data, one\u2019s own experience, external construction cost data, or comparable completed projects.<\/p>\n\n However, it is important never to view such figures in isolation from the specific project. Location, timing, building standards, construction, and technical requirements can have a significant impact on actual costs. <\/p>\n\n A calculated total alone does not make for a good cost estimate.<\/p>\n\n The results should be reviewed for plausibility. Cost categories that stand out, unusually high or low key figures, and significant changes compared to previous planning stages should be examined more closely. <\/p>\n\n Comparing the figures with previous cost estimates is particularly important. For buildings and interiors, the HOAI explicitly requires that, during the design phase, the cost calculation be compared with the cost estimate. <\/p>\n\n The key question, therefore, is not just: How high are the current costs?<\/strong><\/p>\n\n Equally important is this: Why do they differ from the previous cost figures?<\/strong><\/p>\n\n Which method is appropriate depends, among other things, on the stage of planning, the available data, and the desired level of detail.<\/p>\n\n A common approach is to multiply the calculated quantities by appropriate cost factors. The more specific the planning becomes, the more precisely these values can be applied. <\/p>\n\n In a component- or element-oriented analysis, for example, individual areas of the structure are examined in greater detail. This makes it easier to understand which design or quality-related decisions result in certain costs. <\/p>\n\n Comparable projects can also provide valuable insights. However, this requires taking into account differences in price levels, region, size, use, and standards. <\/p>\n\n Model-based cost estimation offers another option. If a properly structured BIM model is available, relevant model information and quantities can be used for cost planning. For example, NOVA AVA supports model-based cost planning based on IFC models through its BIM add-on. <\/p>\n\n Regardless of the method used, however, a detailed calculation is not automatically a reliable one. The quality of the underlying information remains the decisive factor. <\/p>\n\n People often try to assign flat-rate accuracy values, expressed as percentages, to the individual stages of cost calculation.<\/p>\n\n For practical cost planning, however, such an approach should be viewed with caution. The actual reliability of a cost estimate depends not only on its designation, but especially on the stage of planning, the quality of the quantity takeoff, the cost data used, and the project risks that still exist. <\/p>\n\n Even a very detailed table can still be inaccurate if outdated quantities or inappropriate cost figures were used.<\/p>\n\n It is therefore important for planners to transparently document assumptions, price levels, and calculation bases. This makes it possible to assess how reliable a cost estimate actually is. <\/p>\n\n Cost estimation and cost calculation are both part of cost planning, but they are based on different stages of planning.<\/p>\n\n The cost estimate is prepared earlier in the project and, for buildings and interiors, is developed as part of the preliminary planning phase. It provides an initial, systematically structured assessment of the project costs. <\/p>\n\n The cost estimate will be prepared during the preliminary design phase. At that point, significantly more specific design information will be available. Quantities and specifications can be determined more precisely, and costs can be calculated in greater detail. <\/p>\n\n Cost calculation does not simply replace cost estimation. Both cost figures should be compared with each other. <\/p>\n\n It is precisely this comparison that highlights cost trends and shows, for example, how planning decisions affect the budget.<\/p>\n\n We discuss the differences between these two stages in greater detail in our article \u201cCost Estimation and Cost Calculation\u2014Differences and Connections.\u201d<\/strong> <\/p>\n\n A cost calculation can be structurally sound yet still lead to incorrect conclusions. In practice, it is often not so much obvious calculation errors as unclear or inconsistent underlying assumptions that cause problems. <\/p>\n\n Insufficient planning:<\/strong> If components that are still largely undefined are already being costed in great detail, this creates a false sense of accuracy. The figures appear more precise than the planning actually allows. <\/p>\n\n Incorrect or outdated quantities:<\/strong> If the plan changes, the affected quantities must also be updated. If this is not done consistently, the cost calculation will be based on different planning statuses. <\/p>\n\n Inappropriate cost benchmarks:<\/strong> Values from older projects or projects that are only partially comparable can significantly skew cost calculations. Current price levels and project-specific conditions must be taken into account. <\/p>\n\n Lack of Structure:<\/strong> If costs are categorized differently across various project phases, it becomes difficult to track the development of individual cost areas.<\/p>\n\n Undocumented assumptions:<\/strong> If qualities, price levels, or specific constraints are not documented, it becomes nearly impossible to reconstruct later how a cost figure was arrived at.<\/p>\n\n It\u2019s not the same as looking at past cost figures:<\/strong> Simply determining the current total amount is not enough for professional cost control. Changes must be identified, analyzed, and explained. <\/p>\n\n A cost estimate must still be understandable even months later.<\/p>\n\n Especially on larger projects, multiple people and specialist planners often work with the same cost data. If the basis for calculations is not properly documented, discrepancies in the data can quickly arise. <\/p>\n\n Therefore, it should always be clear what planning status is being used as a basis, what quantities were used, what sources the cost figures come from, what price levels they reflect, and what specific assumptions were taken into account.<\/p>\n\n In addition to structured cost determination, DIN 276 also emphasizes the documentation and control of costs.<\/p>\n\n Transparent documentation not only facilitates current cost planning; it also lays the groundwork for future comparisons and decisions. <\/p>\n\n The benefits of a thorough cost estimate become particularly evident in the subsequent project phases.<\/p>\n\n During the preparation for the award of the contract, costs are determined based on the Bill of Quantities priced by the designer and compared with the cost estimate. The HOAI also requires that, as part of the participation in the award process, the results of the bidding process be compared with the priced Bill of Quantities or the cost estimate. <\/p>\n\n This makes the cost estimate an important reference point for the project’s further development.<\/p>\n\n Consistent cost planning makes it possible to identify changes before invoices are received. Instead, the results of planning, bidding, and contract awards can be continuously compared with previously defined cost levels. <\/p>\n\n That is precisely why cost estimation, bidding, and billing should not be viewed as separate tasks.<\/p>\n\n To ensure transparent cost planning, a wide range of information must be integrated. This is exactly where NOVA AVA comes in to help you. <\/p>\n\nWhat is a cost estimate?<\/h2>\n\n
When will the cost estimate be prepared?<\/h2>\n\n
What role does DIN 276 play in cost calculations?<\/h2>\n\n
Cost Group<\/th> Contents<\/th><\/tr><\/thead> KG 100<\/td> Property<\/td><\/tr> KG 200<\/td> Preparatory Measures<\/td><\/tr> KG 300<\/td> Building – Building constructions<\/td><\/tr> KG 400<\/td> Building \u2013 Mechanical and Electrical Systems<\/td><\/tr> KG 500<\/td> Outdoor Facilities and Open Spaces<\/td><\/tr> KG 600<\/td> Furnishings and Artworks<\/td><\/tr> KG 700<\/td> Construction-Related Costs<\/td><\/tr> KG 800<\/td> Financing<\/td><\/tr><\/tbody><\/table><\/figure>\n\n What information is needed to calculate costs?<\/h2>\n\n
How is a cost estimate prepared?<\/h2>\n\n
1. Check the status of the plan<\/h3>\n\n
2. Derive quantities from the plan<\/h3>\n\n
3. Organize Costs<\/h3>\n\n
4. Link Quantities to Cost Rates<\/h3>\n\n
5. Validate the results<\/h3>\n\n
What methods can be used to calculate costs?<\/h2>\n\n
How accurate is a cost estimate?<\/h2>\n\n
Cost Calculation and Cost Estimation: What’s the Difference?<\/h2>\n\n
Common Mistakes in Cost Calculations<\/h2>\n\n
Why Documentation Is Just as Important as the Calculation<\/h2>\n\n
From Cost Calculation to Ongoing Cost Control<\/h2>\n\n
Performing Cost Calculations in a Structured Manner with NOVA AVA<\/h2>\n\n