When it comes to the construction industry today, sustainability is a concern that is at par with affordability, convenience and durability. Modular housing has been picking momentum in the construction industry due to affordability and convenience but also for its multi-factored sustainability benefits. In this article we will discuss:
- How are modular homes sustainable?
- How to evaluate the sustainability of a modular home? – A Case Study
- What are some sustainable building materials for modular homes?
- 5 eco-friendly tips for green modular homes.
An environmentally sustainable building approach requires a holistic consideration of all aspects that minimize and optimize the consumption of energy, water and materials and reduce the environmental footprint of the built-up:
a. Minimizing waste and conserving resources
b. Reducing energy consumed in various building processes
c. Ensuring a sustainable lifecycle of materials from mining and transportation to disposal
d. Reusing and recycling of materials and
e. Ensuring responsible construction and demolition waste disposal
Prefabrication and offsite manufacturing contribute to a large percentage of new building construction all across the world that are looking for energy efficiency and are touting modular homes as the future of sustainable building construction.
How are modular homes sustainable?
The construction industry is responsible for around one-third of global energy use and one-third of global greenhouse gas emissions, both in developed and developing countries . According to the LafargeHolcim Foundation for Sustainable Construction, “Sustainability embraces the environment and its long-term endurance as a matter of concern for all humanity.” Considering the huge amount of energy and resources to build and operate the construction industry as well as the emissions and waste generated, the sustainability of all construction must perform well on all three parameters- environmental, economic and social:
What are the environmental factors that affect sustainability in modular homes?
Modular building offers more control over all aspects of production of the modules which significantly contributes to its environmental benefits. This means energy and resources are utilised much more efficiently while also causing less wastage in the factory and on-site. This ultimately reduces the environmental footprint of the construction.
- Energy and water consumption: Modular construction uses building processes that are energy and water efficient such that the prefabrication is 50% more efficient at using sources of energy, 30% more efficient at using water and 40% more efficient when it comes to using raw materials .
- Reduction in harmful emissions: In modular construction, there is a significant focus on use of materials that are healthy for occupants by the use of non-toxic and low VOC (Volatile Organic Compounds) materials which do not release chemicals into the atmosphere that cause detrimental health effects.
- Reduction of waste: Modular construction consists of manufacturing modules in factories that are built to very specific measurements. This ensures that there is efficient use of materials with minimal wastage. Since modular homes are assembled to stringent guidelines on site, studies show that they can reduce construction waste by 40% .
- Optimal usage of manufactured materials and natural resources: One benefit of modular construction is the efficient usage of material. Raw material efficiency can be increased by up to 40% during production in factories as can the use of recycled materials in partition walls and insulation on site.
- Overall environmental impact: Modular building construction can significantly bring down energy usage in both production, operation and maintenance. Well planned insulation and self-sustainable modular homes (eg: solar powered) can help bring down energy consumption up to 72% that greatly reduces its carbon footprint. The production being in a controlled environment in a factory means materials and labour are less susceptible to natural hazards of wind, fire and rain. There is minimal intervention of the site except the installation of a permanent foundation that significantly brings down environmental impacts (eg: machinery) by 30-70%.
What are the economic factors that affect sustainability in modular homes?
Modular construction has major economic benefits that lend it the additional advantage of economic sustainability. Modular homes work on space optimisation that bring down costs that are associated with unnecessary wastage of space in a home. Modular makes optimised use of raw materials in construction and the replication of these modules on a large site significantly affect the economy of the construction, in that the costs are reduced to a large extent. 5-20% cost reduction is observed in modular homes as compared to traditionally built construction.
A study conducted in 2012 by BRANZ in New Zealand regarding the economics of pre-fabrication underlined the following: 
- Modular home construction is almost 50% faster than traditional construction. This reduction in construction/assembly time brings around a savings of $1000-$1600 per week.
- General productivity (in labour) is also greatly improved in modular construction (up to 10%) and even a 1% increase in productivity in factory and on-site directly translated to $139M to the New Zealand economy.
These observations clearly point towards modular construction being more economically efficient in that it brings down construction costs, there is a reduction in defects and wastage in manufacturing and assembly and there is a significant savings in construction time. This makes modular construction cost effective and efficient, including some other factors like reduced land holding costs and a net increase in construction per year that would lead to more profit.
There are many factors that influence the social sustainability of a modular construction where despite the technical benefits of this construction there is a defined attitude towards the perception of modular construction. By its very definition, modular construction is repetitive. But this repetitiveness is often equated to not being original or customised to the user’s requirements. This unfortunately affects the social acceptance of modular housing. It is incorrectly assumed that modular houses are temporary and not economical. Some factors that ensure the social sustainability of modular homes is the increased safety of labour due to fewer accidents on site. Modular construction leads to significantly lesser human errors in both manufacture and assembly and the processes afford more safety and healthier workplaces for all stakeholders involved.
How to evaluate the sustainability of a modular home? – A Case Study
A 2014 study investigated how modular construction can support sustainability in the built environment through a detailed case study of ‘The Stack’, a recently completed modular rental housing block in New York City. The design, manufacturing and construction processes were studied and analysed to derive how modular processes can fulfil sustainability goals in construction industry. Let’s examine these processes in detail: 
What is the Modular Design Process?
The design of a modular home consists of choosing a project delivery system. This system ensures to organise the design, manufacturing, and construction services for a building. The developers chose first an architecture firm (Gluck +) and then an innovative modular manufacturer (Deluxe Building Systems), based in Pennsylvania for the project. Some factors that contributed to this decision and affected the sustainability of the end product included: their experience with steel modular manufacturing, their specialisation and expertise in modular engineering, their financial strength and the location of the manufacturing facility closer to the construction site. A collaboration between the developers, designers, client and modular manufacturer ensured a design process that took into account:
- Pricing of the manufacturing process
- Developing efficient logistics between the manufacturing plant and construction site
- Designing and solving all structural and engineering issues involved in modular construction
- Preparing mock-ups for elimination of error in design
- Developing lean approaches for manufacture of modules for more efficient design and waste management in every step of design
- Sustainable procurement of materials
This detailed design process took care of efficient management of resources and materials that would optimise their usage in manufacturing and assembling. Developing streamlined logistics between them would ensure that the project schedules are shortened to a large extent that brings sustainability of economics by reducing project budgets. This process also eliminates the unnecessary wastage of resources and materials used in a project by arriving at an efficient system in a controlled environment.
What is the Modular Manufacturing Process?
The Deluxe Building Systems developed shop drawing packages for the manufacture of the modules for the 28 residential units at their factory in Pennsylvania. The shop drawing packages included the details for each part being produced. They also adopted lean fabrication practices to improve the module production efficiency and reduce potential waste during production. Two examples of this sustainable manufacturing process: 
- The members of each module’s steel chassis were cut via computer numerical control (CNC) cutters using a laser and water jet. Bending was done by hammering with press brakes and similar tools. The steel chassis was assembled by manual and robot welding.
Since the metal fabrication was completed at the factory with efficient tools and expert welders, it was possible to increase the process efficiency and reduce steel waste. Since the process is streamlined, material wastage and energy consumption in production is greatly reduced as compared to conventional construction process.
- Gypsum board was cut by an automatic gypsum board cutting machine. The pre-cut gypsum board was nailed to the cold-formed steel walls using the fully automatic drywall board manufacturing machine.
These tools significantly improved production efficiency, with minimal waste due to precise cutting and nailing. As these procedures were all conducted inside a factory building, there was also no danger that the gypsum board would suffer from water damage due to exposure to the elements, which is often a problem on conventional building sites.
What is the Modular Construction Process?
The modular construction process follows the conventional building method by the digging of a permanent foundation. This provides the adequate base for the stacking of the modules first floor onwards. The modules were transported from the manufacturing plant in Pennsylvania to the construction site in New York by adopting a lean concept for just in time delivery and production that allowed them to eliminate waste in terms of both manpower and time.
- Highly experienced crew assembled the modules on site using cranes and all modules were lifted directly from the flatbed trailer into their final location. This significantly reduced the errors in the module assembly process on site.
- After all modules were stacked according to the design, only field finishing work was left. Most finishes were applied in the factory itself which increased the economic benefits of modular construction.
- In all, 56 units were stacked after which the external façade was installed. Almost 50% of the work tasks were executed in the factory itself and hence the assembly of modules only took a short period of two months.
A Comprehensive View of Sustainability in Modular Homes
Several inherent opportunities offer advantages of sustainability in modular construction. The project schedule can be significantly shortened by the efficient planning of the project, increasing productivity of materials and manpower and lesser weather related delays as most processes are carried out in a controlled environment. There is minimal material wastage by a streamlined production process and reduction in carbon emission by transporting of only finished modules to site instead of multiple visits with raw materials.
The Stack had a shorter project duration of up to 30% as compared to standard construction. This reduction in construction period was due to off-site construction carried out in the plants. This helped the economic sustainability of the project by cost savings from the project’s financing costs. All manufacturing processes and assembly produced high quality of finished housing units for occupants that would reduce the operational energy consumption of each unit during the building’s life. This will cause a direct reduction in carbon emissions from the consumption of energy and also reduce the subsequent energy bills for the occupants.
Some units of the Stack were assigned to low and middle income group persons under social housing and addressed the need for affordable housing in the densely populated New York City. Also modular building provides a safe and healthy work atmosphere for workers who are also not exposed to hazardous work conditions that are affected by weather and temperature extremes. There is a significant reduction in traffic complaints and dust, noise and other pollutants on site that causes less disputes with neighbouring sites.
The Stack minimised job-site environmental impacts by reduction in material waste, air and water pollution, dust and noise, and overall energy costs. Two important benefits of modular building are a significant reduction in construction waste and need for resources. Also at the end of the life of a modular building, it can be easily dismantled, separated into components, recycled and reused all over again. There is also a reduction in energy consumption during the building’s operational lives which greatly controls its carbon footprint.
What are some sustainable building materials for modular homes?
Modular homes employ the use of energy efficient and sustainable building materials. Lean design and manufacturing processes ensure minimal wastage of building materials and maximum recycling of construction waste:
- Roof and wall panels: Modular homes focus on the excellent insulation for energy efficiency. Quality insulation ensures that not much energy is consumed to heat or cool buildings. Wood is a renewable and recyclable insulating material for roof and wall panels and modular homes employ the use of certified and sustainably sourced timber. Steel also has great insulating properties while also being completely recyclable upon dismantling. Roof panels and internal walls are also made of durable recycled materials.
- Windows and Doors: In modular homes, windows and doors are built using certified materials that can withstand all building loads and have excellent insulation properties. Recycled aluminium is widely used as a sustainable material and its manufacturing and construction waste are infinitely recyclable. Green modular homes also employ windows and doors that are rated for their energy efficiency.
- Floors: Timber, steel, concrete and bamboo are materials that are commonly used for floors in modular homes. Timber and timber grade bamboo are sustainably sourced and certified to the highest green building standard. All these materials also provide excellent insulation in modular homes.
- Modular homes use renewable and recycled materials that also emit lesser harmful chemicals. They also use paints, sealants and adhesives that little to no volatile organic compounds or VOC. This makes for cleaner and healthier environments in the long term.
5 eco-friendly tips for Green Modular Homes.
- Green modular homes can be installed with equipment to harness renewable energy such as solar panels and wind and water mills depending on the local climate factors and location of site. The house can produce most to all of its own energy requirements for lighting, heating and cooling. Extensive planning can even help the house to function off-grid and significantly reduce its carbon footprint.
- An important consideration for green modular homes is to plan for efficient insulation that prevents the loss of heating and cooling and reduces the subsequent energy bills. Installing energy efficient doors and windows offers great insulation and a reduced electrical load. Sustainable options such as certified energy efficient wood stoves can also be used for heating.
- Energy consumption can also be reduced by design that incorporates natural lighting in the modular home. This reduces the need to use artificial lighting during the day. LED or CFL lighting should be used for energy efficiency.
- A green modular home can harvest enough rainwater to fulfill its own water requirements. Rain water harvesting tanks and a treatment system can be installed to collect and treat rain water so that it is potable and be used for kitchen and gardening purposes. A grey water treatment tank attached to the kitchen and laundry is also an efficient system to recycle and reuse water and reduce environmental pollution.
- Energy can also be saved by installing an energy efficient plumbing system. Pipes made using certified green materials and appropriately routed to reduce pipe lengths can significantly reduce heat loss and save a lot of energy. Water consumption can also be reduced by using water efficient showers and faucets and the use of a low-flush toilet that uses much less water than a conventional toilet.
Modular housing fulfil all the aspects of sustainability and can provide a holistic sustainable experience to occupants throughout the lifecycle of the building. All processes in modular building can be further customised to be eco-friendly by the installation of green plumbing and HVAC systems that use low energy, recycle and reuse water and also use alternate means of energy production such as solar powered roof panels. All of these interventions significantly bring down the energy and carbon consumption of the modular building.
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 Ahn, Yong Han & Kim, Kyoon-Tai. (2014). Sustainability in modular design and construction: a case study of ‘The Stack’. International Journal of Sustainable Building Technology and Urban Development. 5. 10.1080/2093761X.2014.985758.