Cost estimation traditionally starts with a Bill import and often involves re-engineering by having to re-measure the quantities off a drawing. This is a time intensive process of having to re-measure the quantities off a drawing, quantifying almost 50% to 80% of an estimators time in a day or on a project tender.
Electronic Quantity Take-off(QTO) is the introduction to BIM. QTO offers the capability to generate take-offs, counts and measurements directly from a 2D PDF,DWFX or IFC file. The software also offers the users to create electronic mark-ups and annotations and share the information with 3rd party members. This provides a process where quantities, global formulas and data information stays consistent throughout the project and changes can be readily accommodated within QTO and updated automatically in the estimating software.
As a result a Quantity Surveyor on site can utilize the estimators take-off and references to drawings with ease and compare apples with apples. Alternatively the Quantity surveyor can with ease quickly calculate work completed and share information visually for a client’s monthly progress certificates or subcontractor’s progress.
BIM vs Bill of Quantitites
With Building information modelling supporting the full project lifecycle it offers capabilities to integrate various costing efforts with estimating software. Architects typically do not provide cost estimates on projects as part of their standard services, but the native capability of BIM to quantify and calculate is changing the nature of project deliverables for most professionals. Typically professional QS when building a Conceptual or “elementary” bill are the first serious effort to predict the cost of a project and align decision making with those estimates. Project information at these early stages is usually general and at a high level. Although BIM models will assist professionals in identifying detailed costs, this will only offer a “Schedule of Quantities” unlike estimating software which produces a Bill of Quantities.
The level of detail encapsulated within a BIM object is represented in building elements (objects, families, assemblies) in a model – which is contained and shared in an IFC (Industry Foundation Class) format to which can be exported to Excel. Future development will allow estimating software users the ability to share cost data on an IFC object within a project model.
Objects and assemblies can be encoded with data in a building information model to some extent. Additional information can be affiliated with objects in an external database as well. Costing applications harvest information from BIM objects in various manners – either enhancing object definitions within the model, or using a unique identifier to link objects to more detailed information stored externally from the BIM application in a database or common data environment (CDE).
Design software offers the capability to generate take-offs, counts and measurements directly from a model.
This provides a process where information stays consistent throughout the project and changes can be readily accommodated. Building information modelling supports the full project lifecycle and offers the capability to integrate costing efforts throughout all project phases.