Urban sprawl and increased population growth are having negative social and environmental impacts. The United Nations projects the world’s urban population will increase from 55% to 60% in 2030 and 68% in 2050. The demand for more housing impacts green space availability, energy requirements, greenhouse gas emissions and more. The construction industry, which accounts for a third of energy and process-related carbon emissions, plays a crucial role in efforts to reduce building emissions. The type of construction affects the embodied carbon or the carbon footprint of constructing a building which can account for large percentage of the whole lifecycle emissions of a building. One of the new strategies that focus on low carbon, adaptive reuse and retrofit, is vertical extensions. VEs are building additions, sometimes referred to as roof stacking, rooftop extensions, or upward extension, that can provide additional floor space in urban areas. 

New opportunities exist for VEs but a knowledge gap in early decision-making for such projects influences selection of VEs as well as potential challenges and solutions to implement them. To investigate this gap, researchers Eunike Kristi Julistiono, Philip Oldfield, and Luciano Cardellicchio interviewed stakeholders including developers, architects, engineers, and contractors. Their paper “Vertical Extensions: Stakeholder Perspectives on Development Decisions and Construction Strategies” in the Journal of Architectural Engineering offers several solutions to VE adoption challenges, including design and coordination, construction logistics, and structural concerns with the base building. This research will help design teams considering VE projects in the future. Learn more at https://doi.org/10.1061/JAEIED.AEENG-1474. The abstract is below.


A vertical extension (VE) involves the construction of additional floor space on top of an existing base building. With growing urban populations and an urgency to reduce building-related carbon emissions, VEs might have the potential to be a sustainable and innovative solution to overcome the shortage of urban spaces. However, despite the growing number of projects and the emerging academic literature, limited research has documented the decisions that inform the development of VE projects or the lessons learned from stakeholders that were involved in their creation. This paper presents the early decision-making processes that are undertaken to select a VE as an appropriate development type to construct in practice, and the common challenges and solutions during its realization, through semistructured interviews with a broad range of stakeholders, including developers, contractors, architects, and structural engineers that have been involved in recently completed VE projects. The results identify that the main driver of VEs is economic profit, followed by sustainability goals and the desire to stay on the same site. The challenges are related to the complex design and coordination of VE projects, and onsite construction challenges. In addition, this paper identifies the diverse structural support and reinforcement strategies that are used in VEs and contributes to the knowledge by capturing the different aesthetic and construction approaches that are used in practice.

Explore the potential of VEs and their challenges in the ASCE Library: https://doi.org/10.1061/JAEIED.AEENG-1474.