The Z6 Environmental Program: Plant Prefab’s Guidelines for Sustainable Design & Construction

Plant Prefab
Apr 22, 2019 · 7 min read
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Plant Prefab aspires to create homes that are as healthy as possible for inhabitants and the environment. The Plant Design Studio is therefore particularly focused on creating an industry-leading sustainability program. Inspired by the “Cradle to Cradle” ethic, we consider our homes’ ecological footprint at every stage, from planning and construction, through a lifetime of operation and change, to the end of its life cycle, when the home or pieces of it must be replaced, deconstructed, or salvaged. As much as possible, we strive to eliminate waste; use as little energy as possible and renewable energy when we need it; minimize indoor and outdoor air pollution; and minimize water use. Overall, we seek to create homes that respect both human and natural systems.

To keep ourselves honest — and to give our customers an objective, third party measure — we use the United States Green Building Council (USGBC)’s LEED Program and the Environmental Protection Agency (EPA)’s Energy Star ® program to clarify our performance.

To get Energy Star certified, according to the EPA, “homes must be at least 15% more energy efficient than homes built to the 2004 International Residential Code (IRC), and include additional energy-saving features that typically make them 20–30% more efficient than standard homes.” Energy Star certified homes qualify for an increasing number of special mortgage programs.

The LEED Program, which stands for Leadership in Environmental and Energy Design, is more comprehensive than Energy Star and covers water and resource conservation, in addition to energy and indoor air quality.
Our first LivingHome was the first home (ever) to achieve LEED Platinum, LEED’s highest level of certification. Since then, twenty-seven LivingHomes have been certified LEED Platinum and five more LEED Gold, making us one of the most experienced designers of homes at the highest level of LEED certification.

However, as a point-based program with relatively few requirements, LEED doesn’t directly address key environmental measures that we believe should always be minimized. As a result, we developed our own internal environmental program, called Z6, which clarifies and quantifies the six key metrics we aspire to achieve/minimize: Zero Energy, Zero Water, Zero Emissions, Zero Carbon, Zero Waste and Zero Ignorance. We do a percent calculation for each Z6 and those with a score of 85% or above are considered achieved. It is worth noting that some of the Z6 (energy, for example) are based on a projection and actual use will certainly vary. Some, such as water, are impacted by tasks that Plant does not do (landscaping). While no LivingHome has yet achieved absolute zero on every measure, the point is to get as close as possible — to minimize, or neutralize negative impact; to constantly learn and improve; and to move into a domain of actually positively addressing environmental issues with elements that, for example, sequester carbon and improve indoor air quality.

The following are details about each Z6 goal, general strategies we use to achieve each goal, and case study information about the LivingHome 6, one of our most popular LivingHomes.

Z6 Goals

Very low energy requirements that are completely satisfied from renewable sources. Reduce energy use as much as possible and produce all power needs from renewable resources.
To make every LivingHome as self-sufficient as possible, we find ways to dramatically reduce the demand for energy (insulation, high performance windows, low energy lights and appliances, etc.) and integrate technologies that produce the majority (or all) of the power it needs.
The LivingHome 6 is 51% more energy efficient than the baseline that is mandated for all new California construction in Title 24. This results in almost 40% less energy use than other, similarly-sized California homes. And that’s not including electricity produced by the solar panels. Most LivingHomes we’ve completed include solar power and many of them have been designed to achieve zero energy or electricity.

No potable water for landscape irrigation and at least 30% less indoor water use than the average home.
To conserve water, all LivingHomes use low-flow water fixtures and are made grey water ready so that waste water from the bath, shower, washing machine, and dishwasher can be used for landscape irrigation. We also advocate native and climate-appropriate landscaping wherever possible.
The LivingHome 6 uses 40% less water for indoor uses than an average home and therefore exceeds our goal. The amount of water required for irrigation is site and climate dependent, but a homeowner in California can reduce outdoor water consumption by more than 80% simply by using native plants rather than a lawn.

Clean indoor air with very low levels of harmful off-gassed emissions, including mold, Volatile Organic Compounds (VOCs), and formaldehyde/urea.
To achieve this, we minimize and/or eliminate the sources of these pollutants from paint, millwork and engineered wood with formaldehyde, wood-burning fireplaces, and poor ventilation. We also include indoor plants that absorb the dangerous compounds.
The LivingHome 6 includes no-VOC paints and stains, formaldehyde-free millwork, and motion control-based vents in the bathrooms that automatically vent humidity that could cause mold. Based on our own analysis, the LivingHome 6 earns a score of 74%, which is more than twice the rating of a standard home.

No construction waste.
Modular design and fabrication processes reduce construction waste because materials do not spoil by being left outside, cut-offs and surplus materials are easily reused, and better workmanship results in fewer mistakes. We also work with fabricators who carefully separate construction waste to recycle as much as possible. We try to use materials that are recycled or reclaimed, as much as possible, and that are Cradle-to-Cradle certified or inspired (see Carbon below).
80–90% of the waste generated during the construction of the LivingHome 6 is reused, repurposed, or recycled. Typical site-built homes score 25% on our waste rating system; the LivingHome 6 achieves a score of 85%.

Carbon required to manufacture and transport the materials and the home itself are reduced as much as possible and any carbon that is expended is offset through a verifiable means.
To reduce the embodied carbon in the home, we use as many reclaimed and recycled materials as possible and try to source materials that are manufactured locally and/or that are Cradle-to-Cradle certified. Carbon offsets are purchased to compensate for the carbon we project is required
to produce the materials, build the home, and ship it to its final site.
We calculated the embodied carbon of the major materials in the LivingHome 6 from the quantity required and published values of carbon emissions. We also included estimates of the carbon emitted by transporting the materials to the factory and, in the form of modules, from the factory to site. Based on our calculations, we estimate that 34 tons of carbon are used to create the LivingHome 6 and we therefore purchase an appropriate number of offsets from CarbonFund (carbonfund.org). The projects funded by CarbonFund range from renewable energy and landfill or dairy farm methane use to energy efficiency and reforestation.

Informed homeowners who are aware of the environmental consequences of their actions. Make people aware of the resources they use in LivingHomes.
Because the behavior of a home’s inhabitants has a significant impact on its environmental performance, we strive to make homeowners aware of their energy and water use. Studies have shown that people who get feedback on their energy use tend to use 20% less than those who are uninformed. A home walkthrough and a manual, as well as an installed smart energy monitoring system, ensure that our homeowners have all the information they need about how their lifestyle choices impact their resource use.
We are able to give our homeowners real-time feedback on the energy and resource usage, letting them know how they can improve their efficiency and reduce their consumption.


Plant Prefab is the first prefabricated design and construction company in the United States dedicated to sustainable construction, materials, processes, and operations. We provide the time and cost advantages of prefabricated construction, without the usual limitations: We can work with your architects (or you can work with ours) to create your own design, or you can choose from one of our award-winning standard LivingHomes and make it yours. We build healthy, high-quality homes for individuals, architects, and developers alike.

All Plant Prefab projects are built in our 62,000 square-foot home factory in Rialto, CA. The Plant Design Studio has fourteen years of experience helping California families build their dream homes. Our LivingHomes have won considerable industry recognition including the AIA’s top sustainable award, the United States Green Building Council’s first ever LEED Platinum rating for a residential home, Architizer’s Jury and Popular Choice Awards, Green Builder Magazine’s Home of Year, Business 2.0 “World’s 11 Coolest Products,” Business Week’s “Architectural Wonders of the World,” and the Sustainable Quality Awards Grand Prize.

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