BIM: A Collaborative Effort to Define the Quantity Takeoff Information Exchange for Use In Building Information Tools

This article presents the collaborative effort between professional estimating associations to develop the Information Delivery Manual (IDM), defining the information exchange about a facility from the design model to the cost estimator. In 2007, the Association for the Advancement of Cost Engineers (AACE) initiated the effort, which has become a project of the buildingSMART alliance (bSa). Since its inception, the American Society of Professional Estimators (ASPE) and the Royal Institute of Chartered Surveyors (RICS) have joined the project.

The project is active and is listed as the Quantity Takeoff Information Exchange (QTie) project on bSa's website athttp://www.buildingsmartalliance.org/index.php/projects/activeprojects/. The project's goal is to establish agreed-upon exchanges at different levels of development of a facility as a means to standardize the information provided for the cost-estimating task. In doing so, QTie will reduce time wasted and streamline the information exchange in a consistent format.  This article begins with an introduction to the IDM concept based on the National BIM Standard (NBIMS) Version 1 -- Part 1, followed by a discussion about IDMs from an estimator's perspective. From there, the article will discuss the QTie scope and its progress to date. The group's work in the collaborative effort is briefly discussed in the following section along with examples of work in the current project's task groups. The article concludes with an overview about the anticipated end product of the QTie project. 

NBIMS was established in 2005 and is a project of bSa. According to the NBIMS charter, its mission is to improve the performance of facilities over their full life-cycle by fostering a common, standard, and integrated life-cycle information model for the architecture/engineering/construction (A/E/C) and facility management industry. NBIMS is intended to serve as a standard that will allow for the free flow of graphic and non-graphic information between all stakeholders. NBIMS relies on subject matter experts within specialized domains of the A/E/C industry to define the standards required across disciplines working in BIM. Domain experts assemble to form workgroups for projects to document the business process and IDM corresponding with the process. 

Figure 1 (below) is an excerpt from NBIMS Version 1 - Part 1 (p. 95) depicting the workgroup formation and tasks for IDM development. An IDM defines the information exchange requirement, which in turn defines the relationship between any two entities. As such, IDMs codify the information exchanges that occur daily in the course of normal business processes. Ultimately, IDMs are the means for information exchange that will facilitate interoperability between the multiple discipline specific software applications in a BIM by providing a structure for the organization of data required for a specific type of exchange. The data required by an IDM is a subset of the entire facility's data model. 

Figure 1. NBIMS development by work group.
 

The QTie project focuses on the IDM specifically for cost estimating in BIM. The project works to identify the information exchange needed from the design model to the estimator for quantification and input into the construction model. The first phase of the project began with AACE and the University of Oklahoma's (OU) development of a process diagram depicting the information needed to complete the quantification of cast-in-place concrete. The images in Figures 2 and 3 display select portions of the AACE and OU project. Figure 2 is a small portion of the process for the quantification of cast-in-place concrete. The diagram reflects the estimator's query of the design model for information pertaining to the task. As the estimator moves through the design model, data is gathered for the quantification task. As object data is extracted from the design model, the estimator performs the quantification task in sub-processes referenced by the page number symbol associated with each aspect quantification activity. 
 
Figure 2. Information Exchange from Design Model to Estimator (partial).

 
 
Figure 3. Information extracted by estimator from design model for input to construction model (partial).
 

Figure 3 depicts the estimator's task of quantification of the data extracted from the design model, processed, and input into the construction model. Each activity within the design model lane includes a symbol with a sub-process mark referencing the tasks associated with each activity. 

The QTie project is scoped into three sub-projects: counting; assembly/quality; and assembly with methods. Figures 2 and 3 are from the assembly with methods sub-project. In addition to the process flow diagram, the project includes defining criteria for the take-off process. The next step for the workgroup is to develop the IDM for each information exchange.

The three sub-projects within the QTie scope represent three different types of take-offs. All quantity takeoffs begin with counting and progress in complexity as an estimate moves through the levels of project development. Typically, the levels of development correlate with the levels of completeness in a project's design as it moves from schematic through construction documents. The project team is working to develop an IDM for quantification of cast-in-place concrete at each level of project development. The workgroup's goal is to demonstrate proof of concept with the cast-in-place concrete process IDM. 

In December 2008, a "Cost Engineering and Estimating Memorandum of Agreement" was signed with the goal being to develop best business processes, practices, and open standards for use by all software vendors in the development of applications that are interoperable and produce reliable and predictable cost-estimation results. Among the signees were the professional estimating associations of AACE, ASPE, and RICS. Since that time, ASPE and RICS have joined AACE in the workgroup for the QTie project. Along with the original three sub-projects, the collaborative effort has advanced another project for which work is progressing among a group of estimators. For this project, the workgroup is defining the basis for establishing consistent quantification of BIM objects. Participants have volunteered for one of four task groups. 

The task groups seek to:

• Define the levels of measurement detail

• Establish implementation strategies coordinated with software vendors

• Define measurement rules for civil/structural/architectural

• Define measurement rules for mechanical/electrical/plumbing.

The Levels of Measurement Detail group is working to cross-reference the levels of development established by other stakeholders in the A/E/C industry for both the traditional and BIM environment. Reference documents for this task include documents from AACE, ASPE, American Institute of Architects, U.S. General Services Administration, and Construction Management Association of America. This activity is considered the first step in establishing a consistent level of development for a project when referenced in the QTie. The next step for the task force is to establish a common list of terms for use in identifying the level of a cost estimate. From there, the task force will associate each level of estimate with the appropriate level of development for a project in BIM. The task force then will begin work on defining rules of measurement associated with the established levels of estimates. A candidate standard for NBIMS is the ultimate goal of the initiative.    

The workgroup holds a general Web meeting once a month. The task groups meet independent of the general meeting on various days and times. The project is seeking participation from anyone with an interest in the quantity takeoff and cost-estimation processes of a project in BIM.