Project Manager Brad Liljequist chronicles the building of zHome, a ten-unit townhome in Issaquah, Washington—the first multifamily zero-energy community in the United States. Part 10: Designing for Disassembly
Note from Brad Liljequist: Patti Southard has been involved in zHome since its beginning in 2006 and has helped inspire and leverage its core goal of market transformation in myriad ways. This is her second guest installment of the zHome blog, written with Kinley Diller.
One of the key principles considered during the design of zHome was that of "Design for Disassembly" (DfD).
DfD is a building design process that allows for the easy recovery of products, parts and materials when a building is disassembled or renovated. The process is intended to maximize economic value and minimize environmental impacts through reuse, repair, remanufacture and recycling. A DfD process involves developing the assemblies, components, materials, construction techniques, and information and management systems to accomplish this goal.
So when all is said and done, how does zHome stack up when it comes to DfD, now that it’s built? To tease this out, I looked at 14 key questions of DfD through the lens of zHome and provided assertions as to what kind of a letter grade zHome might deserve under each. The overall grade worked out to an A-.
1. How long will the buildings last?
Structures designed to be highly adaptable yet durable will outlast their less flexible counterparts. zHome was intentionally designed for long term durability and to be an integrated part of its community. zHome is anticipated to be around for at least 150 years. Grade: B
2. How easily can the building be transitioned to different uses?
A building that can easily be adapted to serve different functions is much more likely to accommodate the changing needs of its tenants over time. zHome has open floor plans and gives the residents a lot of flexibility of layout, minimizing the need for future remodeling. However, the layout and wall materials between units make it a poor candidate for conversion to other uses such as apartments, retail, etc. Grade: B
3. What will happen to the building when it has reached the end of its life?
Any structure that lends itself to disassembly by hand has a much greater likelihood of passing its genetic code on down to the next generation of buildings. zHome was originally designed as a panelized system that could be disassembled and the panels reused elsewhere, though a crane and truck would be needed to move the panels because of their size and weight. Grade: B
4. How easy will the building be to maintain?
Using products and techniques that allow for easy building maintenance will not only reduce operating costs, but will also reduce the need for replacement and renovation long term. At zHome, a lot of thought went into the durability and ease of maintenance of everything from the finishes to the mechanical systems. For example, the ground source heat pump system is extremely durable, and could possibly outlast the building. Grade: A
5. How efficient is the building (energy, water, human, etc.)?
In addition to the usual concerns of energy and water, a little time should be spent considering human efficiency. zHome is extremely efficient when it comes to energy and water, and the layout of the units makes for fairly compact and efficient human movement. Grade: A
6. How adaptable will the building be to changing local climate conditions?
If you want your building to last through the decades it’s going to need to either be designed to withstand what nature sends its way or to float above it all. zHome is built with rainscreens and significant overhangs which should afford it significant weather protection. It also is designed well for passive ventilation and minimal energy input needs. Grade: A
7. Will the people taking the building down in 100 years know how to disassemble it? Will the tools to do so be readily available?
If you design your building so it can be disassembled by hand and with tools that need no electricity or gasoline, you can be fairly sure that the building will be able to be reused no matter what state our post-peak oil future may be in. zHome’s connections are fairly evident, although the size of the panels are such that a crane will be needed for disassembly. Grade: B
8. What connections are used between the different building elements?
How easy are they to undo? Adhesives severely compromise the adaptability of a structure and impede the regular replacement of those building components with shorter lifecycles. zHome greatly minimizes adhesives at the jobsite, and all of the panels are lag bolted together. The panels themselves were made offsite and designed to be durable and reusable – further disassembly of the panels would be very difficult. The stairs were designed to be easily unfastened, moved and reused. Grade: B
9. Will people who use the building like it?
Buildings that people like feel the love, while buildings that don’t get neglected. And neglect begets water damage that begets mold. Finally, mold begets the wrecking ball. zHome has a pleasant, timeless feel and aesthetics which should keep people loving it for a long time to come. Grade: A
10. How toxic are the building materials?
A little thought, research and guesswork now can go a long way toward making your structure a much less costly endeavor to repair, maintain and disassemble in the future. zHome went to great lengths to keep out toxic materials, including zero formaldehyde in the building and all caulks and finishes were zero or low VOC. Electrical conduit did end up being PVC due to cost and oversight issues. Grade: B
11. How long will the different layers last?
Remember that the bond between two layers must be replaced every time either of the materials is replaced. The materials selected for zHome were chosen for their durability with an eye toward reducing the replacement frequency of materials. zHome installed 50-year siding and 40-year roofs. Grade: A
12. How many different materials are going into the building?
A key DfD principle is to minimize the number of different types of components and materials so that when it comes time to renovate or deconstruct there are large marketable quantities of similar materials that can be recycled. zHome has a fairly diverse palette of materials which will create a lot of work keeping items separated when the buildings come down many years from now. The diversity of materials was in part due to the fact that one goal of the project was to showcase different regional green building products. Grade: C
13. Who else has been asked to think and provide input on these issues?
Taking human nature and long-standing maintenance procedures into account from the get-go will result in a much higher level of user satisfaction (and thus user upkeep). The entire zHome team worked collectively on these issues while utilizing an Integrated Design Process. Grade: A
14. How will the mechanical, electrical, and plumbing (MEP) systems be run through or attached to the building? Can these systems be minimized?
Planning your layout and minimizing MEP runs helps reduce cost and complexity. At zHome this was carefully considered and reworked through the WaterSense certification program to minimize hot water runs. Mechanical systems are located centrally for easy access. Grade: A
There were many instances with zHome where the Integrated Design Process uncovered strong synergies between the DfD principles and the desire to cut C&D waste. One example of this was that by utilizing an exposed frame system (making the project simpler to deconstruct at a later date) no ceiling panels were needed, thereby eliminating waste from cut remainders and miss-cuts.
Another key principle for the construction of zHome was to reduce the amount of materials ending up in the waste stream. In addition, zHome is being recognized by King County as a CleanBin jobsite for their commitment to keeping C&D garbage separate from C&D recyclable material. zHome earned a strong A+ with an overall diversion rate of 98 percent!
For more information on Design for Disassembly please read the DfD guide, which is available by going to www.GreenTools.us and doing a search for DfD.