Figure 1: A breakdown of global CO2 emissions by sector (Why the Building Sector, 2020).
Luna Oiwa is a student in the Master’s in Engineering Management program at Cornell University, interested primarily in sustainable buildings. She organized Cornell University‘s Business Impact Symposium, which our Founder & Principal, Drew Shula, participated in this March.
She currently serves as a Built Ecology Intern at WSP USA, having previously worked as a Project Manager at Cornell Sustainability Consultants and a Project Intern at Taitem Engineering. This essay was originally submitted to a Cornell-run essay competition, in which it earned first place.
Climate change is indisputably one of the most important topics of the day. Less clear is our ability to pinpoint exactly who is to blame or to be held responsible for its increasingly catastrophic consequences. Does the burden fall on consumers or industry, on developing or developed nations? Is it right to assign guilt to the current generation of Earth’s inhabitants, when we inherited already-broken systems from past generations?
But most importantly, what can we do about it right now? One approach that can be used to unpack the complexity of the issue is to look at the data— and that data can lead to some surprising results. Amidst an economic shutdown in the face of the COVID-19 pandemic, global greenhouse gases have been predicted to decrease only 5% in the year 2020 (Storrow, 2020). This is a disappointingly meager decline given the immense amount of change that the global economy has undergone in recent months. It can be seen as an indication of how little a difference it makes when consumers make efforts to cut back on their carbon footprints through personal lifestyle changes. The major issues at hand are instead rooted in systems, and resolving them requires system-level changes (Bardaglio, 2020).
As the industry liable for 40% of global greenhouse emissions, this truth is especially pertinent for the building industry (Why the Building Sector, 2020). The building industry is responsible for 88 million tons of C&D waste per year in the US, about 40% of the nation’s total landfill waste output (Sajip, n.d.).
In light of this data, what would the necessary “system-level change” to address environmental impact look like for the building industry? This paper will attempt to answer this question through a discussion of three relatively recent innovations in the realm of building: modular construction, 3D-printing of building components, and design for disassembly (Dfd). The major metrics used in comparing the environmental impact of these innovations with the traditional processes and technologies they are set to replace are (1) material use and material waste, and (2) energy use and emissions. While this paper will place a focus on environmental sustainability, it also acknowledges the importance of economic and social sustainability by examining issues such as cost, regulatory compliance, and labor requirements.
Modular construction is a construction method in which a substantial portion of a structure is pre-built in an off-site factory before being transported to the project site for final assembly. Modular construction is not a new concept in the U.S. In the post-war years of the 1940s and 1950s, government-backed modular construction became a popular means of providing housing for war veterans. The subsequent decline in the demand for such housing, coupled with the Ronan Point tragedy of 1968— in which a partially prefabricated apartment complex underwent catastrophic failure— led to decreased American interest and trust in the concept of modular construction (Bertram, 2019).
However, recent demand for affordable housing, skilled labor shortages, and developments in Building Information Modeling (BIM) and other technologies that would facilitate the modular build process all appear to be encouraging a resurgence of an interest in modular construction among the American public. Between up-scale hotels such as the AC Hotel New York NoMad in New York City and custom-made residential homes such as those built by Ithaca’s own Carina Construction, “modular” building has become more widely accepted as a method that can produce high-quality results at reasonable cost. In fact, this enthusiasm is expected to grow: according to the Modular Building Institute (MBI), modular construction will increase from 3% to 5% of all new commercial construction in North America over the next five years.
Figure 2: Modular house construction at work (photo taken during an internship).
Material Use & Material Waste
Traditional construction methods are inherently wasteful. Even at an institution like Cornell, it is difficult to ensure that recyclable waste is diverted from landfills unless workers are held by contract to meet requirements set by the LEED green building standard (King, 2019). There appear to be few incentives in place for waste diversion: it takes time on the part of the project manager to educate contractors on proper waste diversion, it takes substantial effort on the part of those contractors to abide by those rules, it creates additional logistic concerns regarding waste pickup, and as a result, increases costs for the building owner. From a life cycle perspective, the additional energy required by the separate vehicles used to pick up recyclables may in fact outweigh the benefits of the waste diversion effort.
Building at a factory— as is done in modular construction— allows for a more organized and pre-established system for waste diversion. It allows for the option of accumulating and storing waste from various construction projects in one area rather than having the separated waste be transported from the project site to the waste processing facility in multiple batches. Studies indicate that modular builds can reduce waste by up to 90% compared to traditional build processes due to better control over inventories, decreased exposure of building materials to outdoor conditions, and more streamlined and efficient build processes (Sajip, n.d.).
Figure 3: Construction and demolition waste (Shooshtarian, 2019).
Energy & Emissions
All else equal, decreases in use of virgin materials and decreases in waste production will lead to decreases in overall energy and emissions. This is due to the elimination or reduction of energy-intensive steps such as resource extraction, material transport, and material processing.
From an energy perspective, another benefit to modular construction is that it reduces the amount of heavy machinery required at a project site. This reduction has the potential to decrease the energy required to operate and transport the heavy machinery, in addition to the amount of energy required to get workers to and from the project site on a day-to-day basis (Du, 2019). The reduced dependence on heavy machinery generates additional benefits such as decreased noise pollution, air pollution, and environmental disturbance in the areas surrounding the project site (Sajip, n.d.).
Lastly, standardization of build processes is made easier and high product quality is maintained in the modular build process due to the inherent advantage of building in a controlled environment. This improved quality aids in ensuring that structures are built to be air-tight and well-insulated. The associated energy and emission reductions across the entire duration of time that the building is occupied can be substantial.
The ability for a building to adapt to the changing needs of its occupants is crucial, as buildings are often renovated or even entirely demolished due to changes in owner or occupant needs far before the building reaches a state of disrepair. In other words, designed lifespan matters little if a building will be taken down before that time is up. Modular builds allow for a greater degree of flexibility in adapting buildings to new specifications and changes in building code; this reduces frequency of renovations, and therefore reduces construction-related energy use significantly in the long run (Bertram, 2019).
Traditional construction often involves many levels of contractors, sub-contractors, and sub-contractors under those sub-contractors. By having the bulk of the build take place at a factory, this hierarchy can be simplified, the project timeline can be reduced by up to 50%, and overall costs can be reduced (Betram, 2019).
Another interesting point to note is that the factory environment may encourage increased automation, due to the controlled environment and reduced need to transport expensive machinery between sites. With less people working on the project and fewer opportunities for human error, modular construction may have the potential of improving worker health and safety in the building industry (Maley, 2019).
3D-Printed Building Components
Another recent development in building technology is the advent of 3D printing. 3D printing involves computer-controlled layering of a material to create a product. The additive nature of this process has the ability to reduce material waste significantly compared to traditional “subtractive” building processes such as wood-cutting.
3D printing was first developed in the 1980’s, but earlier printers were expensive and limited in functionality. Interest in the application of 3D printing in the building industry has recently been revived, in part thanks to the development of BIM software. Today, many 3D printers designed to construct houses, bridges, and the like have been built with the support of major civil engineering companies and research institutions from around the world. The bulk of 3D-printed building projects in current media involve printing of the entire primary structures, walls, and foundations of buildings, but printers have the potential to be used for smaller building components as well.
Figure 4: 3D printing process of a building in Africa (Be More 3D, 2019).
Material Use & Material Waste
The two main printing technologies are Selective Laser Sintering (SLS) and Fused Deposit Modeling (FDM). SLS is a process in which a laser is used to melt particles of a powdered material together. FDM is a process in which ductile materials are extruded through the head of a nozzle, and hardened while cooling. While SLS utilizes materials with high strength and flexibility (such as polysterene and nylon), FDM utilizes thermoplastic fibers that can be used in conjunction with a wide variety of materials, such as wood fibers, metal, and sandstone (Hager, 2016). One project in particular that capitalizes on modern 3D printers’ ability to use a variety of materials is Gaia, or RiceHouse, a project created by the Italian company WASP. WASP made a point of using soil and waste byproducts of rice production for this project, in order to demonstrate the potential for the technology to bring about truly local sourcing of materials (Chiusoli, 2018).
3D printing has introduced the option of creating irregularly-shaped building components that were previously too costly and impractical to manufacture. From a material waste perspective, this is wonderful news: if developed correctly, this could create a world in which structures are completely optimized to use only the minimum amount of materials to meet desired strength criteria, reducing overall resource consumption and perhaps altogether eliminating the need for C&D waste diversion protocols.
Evidence of material use reduction can already be seen in popular 3D-printed buildings of the day. With 3D printers, using less material can save not only physical resources, but also time: it becomes practical to build hollow walls with a wider range of materials. Taking this even further, 3D printing can be paired with finite element analysis and computational design software to optimize structures for particular load conditions. Of particular relevance is Computer-Aided Optimization (CAO), a type of software that takes inspiration from the natural growth process of trees to shape structural models with the intention of creating a uniform stress distribution across any added piece of material. A similar type of program is the Soft Kill Option (SKO), a type of software that takes inspiration from the natural process of adaptive bone mineralization to build structures that are weakened at underloaded points and reinforced at points experiencing high loads (Baumgartner, 1992). This type of detailed structural analysis may be the ultimate way of reducing material use for particular needs.
Energy Use & Emissions
The 3D printer of the construction world is a highly sophisticated piece of machinery that can do what previously took multiple less-efficient pieces of equipment. Assuming that construction printers of the future will be reasonably durable and not too difficult to transport, the use of 3D printing can decrease the amount of energy required for overall equipment transportation and operation, and thereby decrease associated emissions substantially.
As with modular construction, 3D printing and an increase in automation across the construction process has the potential to improve worker health and safety in the building industry. However, it is important to note that the decreased need for human labor may lead to a backlash concerning unemployment.
Another challenge exists in meeting building codes and local regulations. As there have yet to be regulations developed that are specific to 3D-printed buildings, it is unclear whether requirements regarding topics such as structural strength, fire resistance, and thermal insulation will be modified in any way to account for an entirely new generation of buildings.
Design for Disassembly (Dfd)
Design for Disassembly is a phrase that applies a life-cycle approach to building: it refers to buildings that are designed to be taken apart at the end-of-life stage, so that their components can be reused in the construction of new buildings. Design for disassembly is a bold proposal to “close the loop” on our current system of extracting raw materials, utilizing them for a finite period of time, and throwing those materials away after one use.
This concept has been implemented more commonly in product manufacturing than in the building industry. However, it is not new to construction: one of the most well-known examples of Dfd as applied to buildings is the case of the Crystal Palace by architect Sir Joseph Paxton. This building was constructed in London’s Hyde Park in 1851. Six months later, the structure was disassembled and reassembled at the nearby Sydenham Hill, where it remained until a fire in 1936 (Merin, 2013).
Several points are stressed in the modern-day approach to Dfd. First, as with modular construction and 3D printing, BIM has been deemed a highly useful technology in the development of Dfd. Several research papers have been written on the niche topic of expanding BIM capabilities to include end-of-life considerations. The hope is that BIM can be used to facilitate documentation of building components, ensure that quality standards are met, and track useful metrics such as build-time durations (Crowther, 2018).
Second, the key is to build for durability. It is crucial to use high-quality materials that will last multiple rounds of use. Third, it is important to be prepared for inevitable maintenance and renovation jobs. This can be done by designing components to be easy to take apart. The modern approach to Dfd has been to envision a building as a series of layers— the envelope, or “skin”; the structure; the MEP system, or “services”; and the interior space— each with different intended lifespans. Rather than demolish and replace entire sections of a building, this approach encourages replacement of only the components that require replacement at a given point in time.
Figure 5: The “layers” of a house according to Dfd principles (Chen et al., 2018).
Material Use & Waste
As can be imagined, Dfd has an enormous potential to reduce the amount of virgin materials utilized and the amount of waste produced across the construction industry. Although recycling is currently a popular option for dealing with C&D waste, reuse may be a good alternative for materials that cannot be recycled.
Energy & Emissions
The embodied energy associated with the built environment accounts for about 20% of total global energy consumption. Even current practices of recycling C&D waste are highly energy-intensive. With the reduction of use in virgin materials, Dfd provides an opportunity to significantly cut down on the quantity of C&D waste produced and subsequently energy wasted worldwide (Crowther, 2018).
However, it is important to note that in certain cases, building components that are designed for reuse will have a higher environmental impact than traditional building components in the event that they are not reused (Eckelman, 2018).
One of the greatest concerns regarding Dfd is whether the quality of materials can be maintained with reuse. Reliability is especially important to address here because Dfd has not been tested in the building industry to the degree that modular construction and 3D printing has. It is not surprising that there is skepticism about reusing building materials, because second use is often associated with inferior quality, and inferior quality is something that cannot be tolerated when it comes to building structures for human use. Many research studies are currently examining this issue, including studies on shear walls with reusable bolted end-plates (Ding, 2020), dowels and other concrete connections (Ding, 2018), as well as alternatives to steel-concrete composite slabs (Eckelman, 2018).
There are many logistical challenges. On the technical side, engineers will need to work towards entirely new specifications in order to make Dfd a reality. These new criteria include a need to minimize the number and complexity of components and connections, eliminate composite materials and structures where possible, eliminate inseparable finishings where possible, improve on lightweighting and durability of components with component transportation in mind, and a need to use BIM extensively, among other things.
It is difficult to predict whether Dfd will prove expensive in comparison to traditional construction. On the one hand, it is a time- and labor-intensive process. On the other hand, Dfd has the potential to “stimulate the creation of a brand new market for… salvage[d] materials” (Rios, 2015).
Because Dfd is so labor-intensive, it has the potential to provide employment for large numbers of unskilled workers. Locally, this can be seen in the Finger Lakes Reuse Center’s deconstruction program (Cohen, 2019). Unfortunately, the Reuse Center’s program was halted by stringent local safety regulations. A similar challenge can be foreseen in regards to Dfd and building codes in general.
Many things currently stand in the way of popularizing the above-described build processes. Among these are a general lack of information, the intimidating up-front costs that come with changing operational processes entirely, building codes and regulatory compliance, and both skepticism and fear of change among building experts and the general public. However, as with any innovation, it can be said here that product quality can improve, costs can decrease, and public confidence can increase as economies of scale and widespread adoption take place.
This is as perfect a moment as there will ever be for the building industry to step up and become part of the solution to the climate crisis. In a way, this conversation has already begun to take place: the industry has been adopting increasingly more ambitious green building standards. The scope of these standards have broadened in numerous ways: for one, the green certification process has gone from involving only building owners to drilling down to the details of working with material product manufacturers (Shula, 2020). This kind of collaboration is absolutely necessary in order for radical changes like modular construction, 3D printing, and Dfd to take root.
Last summer, I had the opportunity to speak with Diane Cohen, the Director of the Finger Lakes Reuse Center in Ithaca, NY. I remember that at the end of our chat, she asked me a question that has stuck with me ever since: “what more can engineering do for waste reduction [and for sustainability as a whole]?” I would like to live in a world in which I no longer feel like an outlier when pushing for sustainability initiatives in my field: a world in which this type of conversation is normalized. I believe the building industry can do better, and I hope that Cornell’s civil engineering department will work overtime to incorporate this mindset in its teachings.
Bardaglio, P. (May 2020). Executive Director of Ithaca 2030 District. Personal interview.
Baumgartner, A., Harzheim, L., & Mattheck, C. (1992). SKO (soft kill option): the biological way to find an optimum structure topology, International Journal of Fatigue, Volume 14, Issue 6, Pages 387-393, ISSN 0142-1123,
Be More 3D Launched the Construction of the First 3D Printed House in Africa. (2019). Retrieved May 18th, 2020 from https://www.3dnatives.com/en/be-more-3d-first-3d-printed-house-africa-111020194/
Bertram, N., et al. (June 2019). Modular construction: From projects to products. McKinsey & Company. Retrieved May 18th, 2020 from https://www.mckinsey.com/~/media/mckinsey/industries/capital%20projects%20and%20infrastructure/our%20insights/modular%20construction%20from%20projects%20to%20products%20new/modular-construction-from-projects-to-products-full-report-new.ashx
Chen, D. A., Ross, B. E., & Klotz, L. E. (2018). Parametric Analysis of a Spiraled Shell: Learning from Nature’s Adaptable Structures. Designs 2018, 2(4), 46; https://doi.org/10.3390/designs2040046
Chiusoli, A. (Sept. 2018). The First 3D Printed House with Earth. WASP. Retrieved May 18th, from https://www.3dwasp.com/en/3d-printed-house-gaia/
Cohen, Diane (Aug. 2019). Director of Finger Lakes Reuse Center. Personal interview.
Crowther, P. (Sept. 2018). Re-Valuing Construction Materials and Components Through Design for Disassembly. Unmaking Waste in Production and Consumption: Towards the Circular Economy. ISBN: 978-1-78714-620-4, eISBN: 978-1-78714-619-8.
Ding, T., Xiao, J., Wei, K., & Lu, Y. (2020). Seismic behavior of concrete shear walls with bolted end-plate DfD connections, Engineering Structures, Volume 214, 110610, ISSN 0141-0296, https://doi.org/10.1016/j.engstruct.2020.110610.
Ding, T., Xiao, J., Zhang, Q. & Akbarnezhad, A. (2018). Experimental and numerical studies on design for deconstruction concrete connections: An overview. Advances in Structural Engineering. (Advances in Structural Engineering, 1 October 2018, 21(14):2198-2214). SAGE Publications Inc. ISSN: 20484011-13694332. DOI:10.1177/1369433218768000
Du, Q., Bao, T., Li, Y. et al. Impact of prefabrication technology on the cradle-to-site CO2 emissions of residential buildings. Clean Techn Environ Policy 21, 1499–1514 (2019). https://doi-org.proxy.library.cornell.edu/10.1007/s10098-019-01723-y
Eckelman, M.J., Brown, C., Troup, L. N., Wang, L., Webster, M. D., & Hajjar, J. F. (2018). Life cycle energy and environmental benefits of novel design-for-deconstruction structural systems in steel buildings, Building and Environment, Volume 143, Pages 421-430, ISSN 0360-1323, https://doi.org/10.1016/j.buildenv.2018.07.017.
Hager, I., Golonka, A., & Putanowicz, R. (2016). 3D Printing of Buildings and Building Components as the Future of Sustainable Construction?. Procedia Engineering, Volume 151, Pages 292-299, ISSN 1877-7058, https://doi.org/10.1016/j.proeng.2016.07.357.
King, T. (2019, November). Cornell Facilities. Personal Interview.
Maley, S., Mar, R., & Sabherwal, A. (April 2019). From the Design Quarterly: Embracing modular and prefab for future-ready design. Stantec. https://ideas.stantec.com/design-technology/from-the-design-quarterly-embracing-modular-and-prefab-for-future-ready-design
Merin, G. (2013). AD Classics: The Crystal Palace. ArchDaily. Retrieved May 18th, 2020 from https://www.archdaily.com/397949/ad-classic-the-crystal-palace-joseph-paxton
Planet Friendly Homes by Carina. (2020). Carina Construction. Retrieved May 14th, 2020 from https://carinaconstruction.com/go-green/
Rios, F. C., Chong, W. K., & Grau, D. (2015). International Conference on Sustainable Design, Engineering and Construction Design for Disassembly and Deconstruction – Challenges and Opportunities. Procedia Engineering. doi: 10.1016/j.proeng.2015.08.485.
Sajip, J. (n.d.) Modular Construction: A Sustainable Building Method. NY Engineers. Retrieved May 18th, 2020 from https://www.ny-engineers.com/blog/modular-construction-a-sustainable-building-method
Shooshtarian, S., et al. (July 2019). We create 20m tons of construction industry waste each year. Here’s how to stop it going to landfill. The Conversation. Retrieved May 14th, 2020 from https://theconversation.com/we-create-20m-tons-of-construction-industry-waste-each-year-heres-how-to-stop-it-going-to-landfill-114602
Shula, D. (March 2020). Cornell Business Impact Symposium. Virtual event hosted by the Johnson Graduate School at Cornell University.
Storrow, B. (April 2020). Why CO2 Isn’t Falling More during a Global Lockdown. Scientific American. Retrieved May 18th, 2020 from https://www.scientificamerican.com/article/why-co2-isnt-falling-more-during-a-global-lockdown/
Why the Building Sector? (n.d.). Architecture 2030. Retrieved May 14th, 2020 from https://architecture2030.org/buildings_problem_why/
Why Energy Efficiency Upgrades. (n.d.). Office of Energy Efficiency & Renewable Energy. Retrieved May 18th, 2020 from https://www.energy.gov/eere/why-energy-efficiency-upgrades