A multi-objective feedback approach for evaluating sequential conceptual building design decisions John P. Basbagill ⁎, Forest L. Flager 1 , Michael Lepech 1 Stanford University, Department of Civil and Environmental Engineering, 473 Via Ortega, Stanford, CA 94305, USA abstract article info Article history: Received 2 November 2013 Received in revised form 8 April 2014 Accepted 19 April 2014 Available online xxxx Keywords: Life cycle assessment Life-cycle cost Environmental impact Multidisciplinary design optimization Sequential decisions Conceptual building design Conceptual design decision-making plays a critical role in determining life-cycle environmental impact and cost performance of buildings. Stakeholders often make these decisions without a quantitative understanding of how a particular decision will impact future choices or a project's ultimate performance. The proposed sequential decision support methodology provides stakeholders with quantitative information on the relative influence conceptual design stage decisions have on a project's life-cycle environmental impact and life-cycle cost. A case study is presented showing how the proposed methodology may be used by designers considering these performance criteria. Sensitivity analysis is performed on thousands of computationally generated building alternatives. Results are presented in the form of probabilistic distributions showing the degree to which each de- cision helps in achieving a given performance criterion. The method provides environmental impact and cost feedback throughout the sequential building design process, thereby guiding designers in creating low-carbon, low-cost buildings at the conceptual design phase. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Multidisciplinary design optimization (MDO) methods exist that allow designers to explore very large design spaces, quickly evaluate many design alternatives, and find optimal or near optimal solutions for various performance criteria. The benefits of MDO methods are well documented in such industries as aerospace, automotive, and elec- tronics. Within the architecture, engineering, and construction industry, application of MDO methods has been shown to yield significant reduc- tions in building life-cycle environmental impact and cost compared to conventional design methods [1,2]. Although MDO has potential to improve design process efficiency and the quality of the resulting product, MDO methods are not widely used within the building design industry, particularly during conceptual design. The conceptual design stage has been recognized as a critical de- terminant of project environmental impact and cost [3,4]. At the con- ceptual design stage, many choices exist for building decisions, such as shape, orientation, massing, and materials for each building component. These decisions are typically made by architects in sequential fashion. For example, the architect may determine the orientation of a building before placing shading devices to minimize building cooling loads and life-cycle costs. Designers may also wish to understand a project's envi- ronmental impact and cost once the wall assembly system has been chosen but before deciding upon the cladding system. Such a multi- objective sequential feedback approach is typical in the Architecture, En- gineering, and Construction (AEC) industry in that project stakeholders often need to evaluate design decision trade-offs for competing objec- tives. For example, a designer wishing to minimize both environmental impact and cost may find that a certain window-to-wall ratio lowers carbon footprint at the expense of greatly increased life-cycle cost. Existing MDO methods do not accommodate sequential decision- making processes. MDO requires all design decisions to be made in parallel, instead of allowing designers to define variable values sequen- tially and thereby understand the impacts for each successive decision. Consequently designers utilizing MDO must decide on all building decisions before receiving feedback on any single design choice. Existing MDO methods therefore do not integrate well with the AEC industry, which relies on flexible and often-changing decision-making processes, especially at the early stages. A new method is proposed that integrates aspects of MDO methods with conceptual building design. By providing feedback to designers after every single design decision and allowing for easy modification of decisions, the method integrates well with dynamic decision- making processes common to the AEC industry. The method can accom- modate a range of building objectives, such as construction schedule performance, indoor comfort, and life-cycle energy use. The research here presents life-cycle cost and life-cycle environmental impact as the performance objectives of interest, since these objectives are recognized as important drivers in building design decision-making processes [5,6]. Researchers have identified several impact categories that are useful in measuring the environmental impact of buildings, Automation in Construction 45 (2014) 136–150 ⁎ Corresponding author. Tel.: +1 847 912 3850. E-mail addresses: basbagil@stanford.edu (J.P. Basbagill), forest@stanford.edu (F.L. Flager), mlepech@stanford.edu (M. Lepech). 1 Tel.: +1 650 723 4447. http://dx.doi.org/10.1016/j.autcon.2014.04.015 0926-5805/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Automation in Construction journal homepage: www.elsevier.com/locate/autcon