23. BIM-Based Quantity Take-Off

Estimating represents an important aspect of the building process that can benefit from computable building information. Quantity take-offs (QTO) are usually performed at different stages of the project and with different purposes (e.g., for cost estimates and auditing). The conventional approach to perform a QTO represents a time-consuming and error-prone process. Relevant building information needs to be extracted from drawings and unstructured documents, which might be outdated or inconsistent. This chapter focuses on the requirements to support BIM-based QTO. Crucial aspects comprise defining a clear project structure as well as establishing a transparent information management. To organize building-related information, the application of a project-specific Work Breakdown Structure (WBS) is proposed. The structure and content of the generated models needs to adhere to the WBS. In this context, geometric and alphanumeric information at various Levels of Detail (LoD) need to be included. Based on these prerequisites, a workflow for an automated generation of QTO is presented.