Cost estimation is a crucial aspect, which influences the successful management of a construction project. Accurate estimations ensure that maximum profits are earned out of the business. A cost estimator is engaged to calculate the near accurate project costs at different stages, and important project decisions are based on this estimation. This is why; accurate estimation becomes all the more important.
BIM, i.e. Building Information Modeling, is a technology that enables estimators/cost engineers avail accurate and detailed information required for estimating the project costs, thus reduce the variability in cost estimates.
According to the American Association of Cost Engineers, “Cost engineering is defined as that area of engineering practice where engineering judgment and experience are utilized in the application of scientific principles and techniques to the problem of cost estimation, cost control and profitability.”
Cost Estimation Challenges and BIM
Ideally an estimator deduces, rather predicts costs based on the production function, empirical cost inference and approximating unit costs for bill of quantities. Cost estimations for a construction project is a daunting task, this is because it is difficult to judge the exact requirement of material quantities based on the design, moreover as the project progresses designs might be altered and requirements might change.
In such a scenario, keeping track of design changes, accordingly estimating material quantities, tracking the changing production functions and accruing the costs at each stage becomes all the more complex. More often than not, projects go over budget and profit margins are compromised.
This is the reason why, BIM modeling has become extremely popular with cost estimators. BIM- abbreviated for building information modeling, is a bottomless information cabinet. Ideally once a 3D BIM model is ready, quantity take offs and project schedule information is loaded into the model. Now the estimated costs against every schedule are added. In a Revit BIM cost estimation model, every department involved in the construction process can see how costs are accrued at every stage.
Any changes in the design at any given point are immediately reflected across the quantity takes offs and the project schedules in a BIM model.
As a result, the corresponding cost estimations are also affected accordingly. Due to this feature of BIM 5D modeling, it becomes possible to know how the iterated changes affect the estimation.
There are three crucial steps to using BIM for quantity measurement and costing:
- Creating 3D models with complete details of the building geometry
- Based on this geometry, dynamically populating the Bills with quantities from the model
- Auto-annotating the 3D models by dynamically linking the bill descriptions and the accrued costs to the project schedules
BIM Cost Estimation and Value Engineering
Cost engineering and value engineering go hand in hand. These two disciplines coexist and evolve by being mutually beneficial. Implementing BIM for cost estimation throughout the construction project furnishes accurate and detailed information, thus, enables engineers take correct and informed decisions. With clear view/understanding of a project, engineers take the best decisions during the early stages of project development, thus reducing the need for value engineering.
Managing Highly Detailed Cost Estimation Projects using BIM Capabilities
Fair cost estimates, also known as bid estimates are usually carried out for evaluating bids, analyzing contract changes and availing permits and approvals. As a project progresses, the level of details and its complexities increase. These complexities can be easily managed using BIM.
Within a BIM model, objects families and assemblies are created; and building information is abstracted based on certain set standards. A graphical representation of this information is created to promote better visualization and easy understanding. Using costing applications, information from a BIM model is culled. Corresponding cost estimations for every process is fed into the database. Now, this database created in a costing application is exported back into BIM, thus loading the model with detailed cost estimates.
Other than costing, several objectives like material take offs, environmental compliance, energy analysis etc can be achieved using BIM capabilities.