02: Cost Estimation

02: Cost Estimation#

image

Description#

Cost Estimation / 5D modelling is a process in which BIM can be used for cost estimates throughout the life cycle of a project. ​It is a process in which BIM can be used to assist in the generation of accurate quantity take-offs and cost estimates throughout the lifecycle of a project. This process allows the project team to see the cost effects of their changes, during all phases of the project, which can help curb excessive budget overruns due to project modifications. Specifically, BIM can provide cost effects of additions and modifications, with potential to save time and money and is most beneficial in the early design stages of a project. Potential Value

  • Precisely quantify modeled materials

  • Quickly generate quantities to assist in the decision making process

  • Generate more cost estimates at a faster rate

  • Better visual representation of project and construction elements that must be estimated

  • Provide cost information to the owner during the early decision making phase of design and throughout the lifecycle, including changes during construction

  • Saves estimator’s time by reducing quantity take-off time

  • Allows estimator’s to focus on more value adding activities in estimating such as: identifying construction assemblies, generating pricing and factoring risks, which are essential for high quality estimates

  • Added to a construction schedule (such as a 4D Model), a BIM developed cost estimate can help track budgets throughout construction

  • Easier exploration of different design options and concepts within the owner’s budget

  • Quickly determine costs of specific objects

  • Easier to train new estimators through this highly visual process

Quantity take-off and cost estimating ​#

In the design stage, the Information Models can generate more accurate quantities for project cost budgeting, project cost control and cost evaluation on design options, etc. as far as practicable. In the tender stage, the Information Models can be used for extracting quantities in the preparation of pricing documents [and the Information Models shall form part of tender information to indicate the design intent layout and the material quantities for the tenderers’ information]. ​

5D modelling / cash flow forecasting ​#

In the construction stage, the Information Models can be used for extracting quantities for project cost control, cost evaluation on the variation of works, cash flow forecast, spending analysis, interim payment, etc. as far as practicable. The 5D Model shall be adopted in the regular project progress meeting to indicate and compare the current cash flow status with the baseline forecast to facilitate project management.

Resources Required#

  • Model-based estimating software

  • Design authoring software

  • Accurately built design model

  • Cost data (Including Masterformat and Uniformat data)

Team Competencies Required#

  • Ability to define specific design modelling procedures which yield accurate quantity take-off information

  • Ability to identify quantities for the appropriate estimating level (e.g. ROM, SF, etc.) upfront

  • Ability to manipulate models to acquire quantities usable for estimation

References for Additional Information#

Lee, H., Lee, Kim, J. (2008). A cost-based interior design decision support system for large-scale housing projects, ITcon Vol. 13, Pg. 20-38, http://www.itcon.org/2008/2 Autodesk Revit. (2007) “BIM and Cost Estimating.” Press release. Autodesk. 11 Sept. 2008. http://images.autodesk.com/adsk/files/bim_cost_estimating_jan07_1_.pdf Dean, R. P., and McClendon, S. (2007). “Specifying and Cost Estimating with BIM.” ARCHI TECH. Apr. 2007. ARCHI TECH. 13 Sept. 2008. http://www.architechmag.com/articles/detail.aspx?contentid=3624. Khemlani, L. (2006). “Visual Estimating: Extending BIM to Construction.” AEC Bytes. 21 Mar. 2006. 13 Sept. 2008. http://www.aecbytes.com/buildingthefuture/2006/visualestimating.html Buckley, B. (2008). “BIM Cost Management.” California Construction. June 2008. 13 Sept. 2008. Manning, R.; Messner, J. (2008). Case studies in BIM implementation for programming of healthcare facilities, ITcon Vol. 13, Special Issue Case studies of BIM use, Pg. 246-257, http://www.itcon.org/2008/18 Shen Z, Issa R R A (2010) Quantitative evaluation of the BIM-assisted construction detailed cost estimates, Journal of Information Technology in Construction (ITcon), Vol. 15, pg. 234-257, http://www.itcon.org/2010/18 McCuen, T. (2009, November 18). Cost Estimating in BIM: The Fifth Dimension. Retrieved September 21, 2010, from Construction Advisor Today: http://constructionadvisortoday.com/2009/11/cost-estimating-in-bim-the-fifth-dimension.htm

Potential Output Information#

Quantity Takeoff Information in Defined Structure Cost Estimate

Source: BIM Project Execution Planning Guide, Ver. 2.2 with minor revisions.