The impact of construction and demolition debris on the environment is staggering. More than 135 million tons of debris from construction sites is brought to U.S. landfills every year, making it the single largest source in the waste stream (Source: USGBC White Paper –Planning for Construction Waste). Reducing the amount of waste in a project is an important part of sustainable building and begins with the design process. Choosing alternative methods of construction such as prefabrication, preassembly, modularization, and off-site fabrication techniques is an effective way to design out waste.
According to the Whole Building Design Guide provided by the National Institute of Building Sciences, construction waste reduction is measured by material diverted by the waste stream divided by the total potential waste:
Quantity of materials diverted from the waste stream / Total potential waste quantity
Most efforts by the green building community, however, have focused on recovery, reuse, recycling or diversion of the waste post-construction, rather than reducing waste on the front end, through better management, procurement, and construction practices.
The U.S. Green Building Council’s LEED rating program recognizes and rewards points for waste that is diverted post-construction, but does not address the issue of waste minimization during construction.
In its LEED NC Version 3.0 under MR Credit 2 it says:
Intent: to divert construction and demolition debris from disposal in landfills and incineration facilities. The LEED rating system awards points for diversion of (recycled or salvaged) 50% of debris (1 point) or 75% of the debris (2 points).
This system ignores and potentially punishes a contractor who actually generates less waste to begin with, and some could argue it rewards contractors for generating large amounts of waste to achieve the goal of diverting 50% of waste.
Consider a typical 2,000 sq. ft. home that generates about 8,000 pounds of waste, or about 4 pounds per square foot - roughly 15% total waste (Source: National Association of Home Builders Deconstruction Series).
Contractor A is able to divert 50% of that waste from the landfill and as a reward, receives 1 LEED point for only sending 4,000 pounds to the landfill.
Suppose Contractor B is resource-efficient and generates 10% waste or 5,333 pounds of waste from the same 2,000 sq. ft. home, but is only able to divert 45% from the landfill. Contractor B sends only 2,933 pounds to the landfill, but LEED does not recognize this effort within its rating system – despite the fact that the contractor sent 26.7% less waste to the landfill on the same home.
Post construction recycling is just one method of reducing the amount of waste that ends up in our landfills. Waste avoidance through lean construction processes and minimization of waste through prefabrication and the use of building information modeling are much more effective techniques.
Modular construction by nature is material and resource-efficient. One of the great economies of modular construction is the ability to assemble repetitive units in controlled conditions. Another is to minimize material waste associated with conventional construction due to weather intrusion and construction site theft. Whole modular units – largely finished prior to arriving at the construction site – can significantly limit construction waste generated at the site and contribute directly to construction site waste management.
Modular construction capitalizes on the ability to move product in controlled manufacturing conditions, and on tight inventory control and project schedules. It is inherently waste conscious and can have minimum site impact if delivered carefully and strategically with respect to site constraints. In addition, since modular builders work in factory controlled environment, they can have many construction projects underway simultaneously in one location, so they are better able to re-inventory materials that may have been allocated to one project, for use in another. With site built construction, a general contractor would send any overage to the recycle or to the dump.
Off-Site Construction offers significant potential to minimize construction waste. Images courtesy Britco Structures.
Modular buildings arrive to a site between 60% to 90% complete and are built of the same materials and to the same codes as buildings constructed by conventional, on-site methods. Further, once assembled, modular buildings are virtually indistinguishable from their typical site-built counterparts. Pictured is High Tech High in Chula Vista, CA by Williams Scotsman. The school is LEED® Gold certified and made of renewable and recycled materials such as sealed lightweight concrete floors and high-density fiberboards.
A report published by the U.K. group, Waste & Resources Action Programme (WRAP) supports the fact that off-site manufacturing processes can help the construction industry reduce waste. Off site manufacture already offers the construction industry benefits in terms of time and cost predictability, health and safety and skills. However, this work shows that there is the potential to make a significant difference to the amount of waste the industry produces (Source: Current Practices and Future Potential in Modern Methods of Construction).
Some of the biggest waste streams in traditional construction are packaging (up to 5%), timber (up to 25%) and plasterboard (up to 36%). Up to a 90% reduction can be achieved by reducing wastes such as wood pallets, shrink wrap, cardboard, plasterboard, timber, concrete, bricks and cement by increasing the use of off-site manufacture and modular construction. WRAP has developed an excellent resource, the “Designing out Waste: A design team guide for buildings” report to help owners and contractors.
Estimates of the levels of site waste reduced using modular construction. Data courtesy WRAP
For example, modular manufacturers have materials delivered to the factory on pallets frequently. However, rather than disposing of the pallets as is common with on site construction, many manufacturers use companies that remove the pallets and even pay a few pennies to makes them available to supplier companies for reuse as is. This direct reuse results in very low embodied energy versus recycling. For modular manufacturers, pallets do not represent part of the waste stream, just a reusable delivery mechanism.
If we as a construction industry are to be serious about waste reduction, doesn’t it make sense to look at both parts of the equation? Why can’t we design out waste to simultaneously minimize the amount of waste generated during construction as well as managing post-construction waste?
About the Author
Tom Hardiman is the Executive Director of the Modular Building Institute (MBI). MBI is the international non-profit trade association representing commercial modular contractors. For more information, visit www.modular.org.