Resilient Housing for Climate Hazard Mitigation

Publication Date: 2023

Abstract

The Geohome project at North Carolina State University is interested creating a hurricane-resistant dwelling with a unique design that draws from nature. The unit’s wood frame emulates the structure of the coastal live oak; its water-, wind- and fire-resistant cement shell evokes the tubular shape of coastal seagrass; its protective window and door coverings embody the protective features of coastal bobcats, and it perches high on protective stilts like a great blue heron to avoid flood damage. These nature-based resilient design features are combined with the aim of improving residential building performance in hurricane conditions. Typical light-wood framing can be unsuited for coastal construction, as evidenced by the $24 billion in North Carolina property damage caused by Hurricane Florence. Having completed the design and construction of a partial prototype in 2020, our team is preparing to construct a computational model of the entire Geohome building and test it using finite element analysis. This report provides an overview of this work in progress.

Introduction

The Geohome project at North Carolina State University re-envisions light wood residential construction to maintain the benefits of affordability, sustainability, and familiarity while increasing resilience to disaster. It offers protection from hurricane- and tornado-force winds, elevation to avoid flooding, and an innovative enclosure system that reduces damage from wind forces. In addition, its unique framing geometry distributes loads more efficiently, reducing wood quantities and cost and its monocoque cladding system protects the building frame, thereby further reducing the amount of wood required and its accompanying cost.

In Summer 2021, construction of a full-scale prototype of a portion of a Geohome building was started at a facility near the campus of North Carolina State University, however COVID-19 closed the facility before it could be completed. In Fall 2023, finite element analysis will be conducted on a computer-based model of a Geohome building. The data gathered from this testing will help determine if the structure can provide enhanced climate hazard mitigation. While constructing a physical prototype before constructing a 3D computational model may seem counterintuitive, prototyping was, in this case, a significant part of the design process rather than an outcome of the computational model-testing phase. This reversal of conventional sequencing has helped to ensure that the next step in the project, computational model construction and testing, will be based on an improved design.

Research Objectives

The following objectives were identified as part of this project: * Develop a collection of nature-based design lessons for resilient, hurricane-resistant housing; * Construct a full-scale partial prototype of a Geohome building; * Conduct a finite element analysis on the computational model of the structure to measure its structural performance characteristics related to wind resistance; * Outfit a prototype with a sensor array for measuring displacement during a hazard event; * Analyze and disseminate the results of finite element analysis and field sensor data testing in order to contribute to climate hazard mitigation and resilient design knowledge; and * Consider the potential for commercial development of Geohome buildings.

In 2018, Hurricane Florence caused significant property damage in North Carolina. Because many of the state’s most vulnerable citizens live in low-quality housing in areas prone to hurricanes and flooding, they were particularly hard-hit by this disaster. Such losses are not necessary and suggest an extreme gap between current building design and the increasing power and frequency of climate disasters (U.S. Global Change Research Program, 2018[^Globa, 2018]). Buildings must not only adapt to this growing multi-hazard environment, they must also be adaptive to the unpredictable effects of future climate change. The incremental change brought about by building code revisions is commendable but cannot keep pace with our changing climate and increasing disasters. As climate disasters intensify, it is all too likely that building codes will fall further behind despite best efforts to keep pace with an increasingly hazardous environment (Urbanek, 2018¹).

The need for resilient buildings that are capable of mitigating the effects of the climate crisis is urgent. Unfortunately, current buildings are not designed to withstand a 100-year flood every decade or a Category 5 hurricane every year. Moving forward, we face choices. We can continue to build the way we have and face ever increasing annual property damages, we can pursue incremental changes to building codes that already lag behind environmental conditions, or—as this research project seeks to explore—we can try to create a new kind of architecture that is adapted to the realities of the 21st Century climate.

Methods

Theoretical Framework

The Geohome project combines nature-based lessons in resilient design with the theoretical underpinnings of systems theory, human ecology, and environmental justice. Systems theory outlines a comprehensive method and cognitive framework for understanding complex systems (von Bertalanffy, 1969²). It emphasizes the role of processes and relationships in understanding, analyzing, and modeling dynamic systems and synthesizing the complex environmental, social, and economic factors of systems. It adopts an integrated human ecology approach to synthesize relevant aspects of human behavior, hazard analysis, and environmental design. Human ecology targets the interrelationships between humans and their environment (Steiner, 2002³). However, a comprehensive systems approach has not been consistently applied to hazard mitigation research. The Geohome project is grounded in systems theory and human ecology to help ensure a comprehensive analysis of the social, environmental, and economic conditions at work in the coastal built environment.

Environmental justice is a critical concern in the development of the Geohome project as well. Socially vulnerable households often inhabit areas more prone to disasters. Environmental justice performance criteria are woven into the goals of the Geohome project and cross-referenced with other architectural and environmental performance criteria to help ensure that the project addresses the 17 Principles of Environmental Justice outlined by the First National People of Color Environmental Leadership Summit (Energy Justice Network, 1991⁴).

Research Question

The Geohome research program is founded on answering a fundamental question: What would a disaster-proof building look like? To answer this question, the project looked to how plants and animals adapt to extreme environments and applied nature's lessons to the design of buildings. Over the past decade, I have traveled to the world’s hottest, wettest, windiest, and snowiest places, trying to understand natural adaptation to extreme environments and I accumulated a collection of design principles based on my observations.

My observations are framed in this document as Nature’s Principles of Resilient Design. The first principle is resilience—the ability to adapt to change. The second is regeneration, which is the restoration or replacement of components, relationships, and processes needed for system health. Efficiency, defined as the minimal expenditure of energy for maximum achievement of or striving for goals, is the fourth principle. Next is diversity, a rich variety of unique components, relationships, and processes. And, finally, interdependence—the tendency for components, relationships, and processes to rely on each other to achieve goals.

As a result, Geohome project design draws from lessons from nature (see Table 1). Its framing emulates the structure of the coastal live oak. Its water-, wind- and fire-resistant shell evokes the tubular shape of coastal seagrass and aquatic tusk shells, which can withstand water pressure even at 2,000 meters. Its protective window and door coverings embody the eye structure of coastal bobcats and it will perches high on protective stilts like a great blue heron, making it less susceptible to flood damage. As coastal live oaks entwines their roots and branches to create a storm-resistant shield, Geohome buildings will use a unique root-like foundation system to distribute loads. These and other nature-based resilient design strategies will help Geohome buildings adapt to nature's forces rather than try to resist them. The result is a new kind of building designed with nature-based solutions to withstand hurricanes, flooding, earthquakes, and wildfires.

Table 1. Architectural Applications of Resilient Plant and Animal Attributes

Study Site

A prototype of the Geohome will possibly be built in the town of Oriental, North Carolina, on the Inner Banks. This area, along with the Outer Banks of North Carolina and Florida, are extremely hurricane-prone. The site is on a large creek, as is typical of many homes on the Inner Banks. The site is lightly wooded with loblolly pine trees, which are also typical of the area. The density of surrounding structures in the prototype site is also representative of typical Inner Banks residential neighborhoods.

Data Collection

The project’s research methods are grounded in environmental justice, data science, and computer simulation testing methods. Strategies for data collection, analysis, and synthesis are grounded in whole building modeling techniques (Pang et al., 2012⁵). Whole building modeling allows a comparison of a building’s actual and expected performance in real time. Building performance simulation will be employed to create a realistic model of real-world building performance (Hensen & Lamberts, 2012⁶). Data will be collected through finite element analysis, then compared to standard building framing performance. Experimental outcomes will test the primary research hypothesis that the structure can provide a safe, affordable housing option that is less easily damaged during disasters.

Once a computational model of the structure is constructed, finite element analysis will be conducted to gauge system response to simulated hurricane forces. Finite element analysis employs engineering calculations to obtain information on the response of systems to loads. Using finite element analysis to obtain such information will reduce the number of physical prototypes and experiments needed and produce test results in a measurable, mathematical format. Results of finite element analysis can then inform the design of the prototype to be field tested with a sensor network.

Before the design and construction of the partial prototype in Summer 2021, data on ecosystem resilience was collected from the Outer Banks and Inner Banks of North Carolina. The purpose of this research was to learn how plants and animals adapt to extreme environments and then apply these nature-based lessons to the design of an innovative system for safer coastal housing. Once a satisfactory design was developed, the partial prototype structure was constructed at a facility in Raleigh. However, the facility was closed in August 2020 due to COVID-19, which halted the construction of the prototype. Nonetheless, valuable lessons were learned about the framing and structural shell of the building during construction. Specifically, strengthening framing was deemphasized in favor of developing a stronger, monocoque shell.

Projected Findings

This section describes a framework for the findings to be determined once results and conclusions of project testing is complete. Data collected from finite element analysis and field testing with the sensor network in an actual natural hazard event will provide a tangible answer to the primary research question of what a disaster-proof building might look like. While the Geohome building is not literally intended to be hurricane-proof, it is intended to go beyond current building codes by employing and testing the nature-based resilient design principles outlined above. The results of data analysis through finite element analysis and field testing will provide answers about the validity of each of the five architectural applications listed in Table 1. The answers revealed by testing will also point toward and answer to an overarching question: Can we create a new kind of architecture adapted to the realities of life in the 21st Century?

Deliverables resulting from the project will include a partial full-scale prototype for hurricane-resistant housing, a 3D computational model of the full Geohome, and test results from finite element analysis. Published results contributing to knowledge on hazard mitigation and resilient design will also be produced. Testing will advance mitigation-related practice by determining the system's viability for further development and deployment in communities often affected by disasters.

Data collected from testing will help the research team refine the design. Such resilient structures could then play a role in improving building codes for a safer built environment and significantly reduced property damage. Looking forward, I aim to partner with industry and community leaders to create affordable, hurricane resistant housing. Specifically, I anticipate that collaboration with the manufactured housing industry will facilitate market adoption of the resulting structures. With nature as our teacher, I am confident that we can adapt our dwellings to our climate so that people of all means can live safely and securely in North Carolina and beyond.

References