21 Acres Center Green Building Features
The 21 Acres Center is the first commercial building in a rural farm setting to achieve LEED ® Platinum
certification by the U.S. Green Building Council. The distinctive, 12,000 square foot building was
recognized with the highest-level certification for its integration of innovative green building and on-site
systems that provide a healthy, comfortable and resource-efficient environment.
The 21 Acres Center features retail space for the 21 Acres Farm Market, a commercial kitchen, classrooms
and educational event spaces. But its most important role is as a living laboratory for green building – an
exemplary structure built and maintained by a non-profit organization that is dedicated to education and
advocacy for sustainable living. This structure enables 21 Acres to provide unique access for the public –
from students and homeowners to commercial builders and industry professionals – to see and experience
cutting-edge green building technologies in action and to learn about the construction, operation and
maintenance of advanced building systems.
Built for Sustainability, Health and Comfort
The design of the 21 Acres Center blends principles associated with green
building – such as resource efficiency throughout a building’s life-cycle –
with the concept of a living building, in which electricity needs are
supplemented with on-site renewable energy generation, water needs are
reduced through the use of low-flow fixtures and composting toilets and
100% of stormwater and wastewater are managed on-site.
By following a deliberate and
iterative design process, the
21 Acres design team
achieved the successful
integration of features and
elements from both green and
living buildings.
The comfort and health of the building’s occupants was a top design
priority. Water filters ensure ultra-pure water for drinking and cooking. The
building interiors provide excellent acoustics and the ventilation system ensures clean, tempered fresh air
when needed. Operable windows provide ample natural light and views of the beautiful grounds and
organic farm surrounding the building. These features, along with the building’s many green technologies,
help ensure that the 21 Acres Center is as comfortable as it is efficient, providing an excellent environment
for work, study and meetings.
Below are some of the green building technologies incorporated into the 21 Acres Center and their ecoimpacts:
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Insulated Concrete Form Walls
Radiant Flooring and Geo-Thermal Heat Pumps
Living Roof and Stormwater Management
Rooftop Solar Panels
Energy Conservation
Indoor Environment: Air Flow, Water Quality and Acoustics
Composting Toilets and Wastewater Systems
Gardens, Grounds and Parking
The Building’s Envelope
Both the energy-efficiency and comfort of the spaces in the 21 Acres
Center begin with the building’s envelope – the walls, floor and roof
– and how these elements integrate with the effects of temperature,
humidity and airflow. Concrete was selected as the primary material
from which to build the walls and floors. To balance and optimize
heat and light without reducing the roof space to be occupied by solar
PV modules, a berm was constructed against the south wall of the
first floor and clerestory windows and translucent roof panels were
installed above the second floor walls. Together, these features work
to reduce the size of – and investment in – heating and cooling
equipment. And with more ambient daylight entering the building,
less energy is required for lighting.
Insulated Concrete Form (ICF) Walls
The 21 Acres Center utilizes thermal mass to maximize solar gain in
winter (reducing heating needs) and minimize solar gain in summer
(reducing cooling needs). Thick, well-insulated walls slowly absorb
heat during the day and release it after the sun sets. Concrete is a
good material for this type of construction, however concrete
contains a substantial amount of embodied energy and its large
carbon footprint challenges its choice as a green building material.
To mitigate this concern, the design team chose to use insulated
concrete forms (ICF). Two different ICF block systems that contain
between 42% and 90% recycled expanded polystyrene (EPS)
insulation were selected to shape the external and internal walls,
depending on the amount of structural support required. Though
more complex to implement in a two-story commercial building with
many window openings, this EPS block wall construction offered the
added benefits of diverting construction material away from the
landfill and reducing manufacturing and transport emissions.
Sustainable Materials Reduce
Embodied Energy
The goal for 21 Acres was to
select building materials that
eliminate or reduce the amount of
embodied energy. Embodied
energy refers to the energy
needed to employ a material
throughout its lifecycle, from its
production to its eventual reuse
or disposal. It includes inputs
such as the amount of energy and
labor used to extract,
manufacture, transport and
install it at the project site.
Green buildings seek ways to
reduce those inputs without
compromising the form and
function of the building. To avoid
waste, when a product or
material contains more embodied
energy, it is even more important
to ensure that it will be durable
and/or have a high potential for
reuse.
The 21 Acres design team
selected groups of materials that
could meet all the of the
building’s form and function
goals while also considering
environmental benefits like
recycled content, local sourcing,
low emissions, certified wood
content or rapidly renewable
content. Each of these attributes
was carefully evaluated for its
overall contribution to reducing
embodied energy.
Eco-impact:
 An ICF containing 90% recycled EPS and used to form teninch thick block walls requires two-thirds less concrete than
conventional construction while retaining significant
thermal and acoustic benefits.
 The ICFs used in the 21 Acres Center structure kept 17,000
pounds of polystyrene out of landfills and saved 576 cubic
yards (58 truckloads) of concrete.
 Industry statistics show that using ICFs in wall construction can result in up to 44% less energy
being needed to heat a building and up to 32% less energy to cool in summer than conventional
construction methods.
Radiant Flooring and Ground Source Heat Pumps
All of the space heating for the 21 Acres Center is provided by the earth via ground source heat pumps and
distributed through a radiant floor system.
For the radiant floor heating, a grid of plastic tubing embedded in the polished concrete floors circulates
warm liquid—a mixture of water and antifreeze—that transfers heat to the people and objects in the space
above. Room thermostats use slab sensors and radiant system valves to modulate and direct heat
distribution to each area. The radiant floor heating provides a comfortable indoor environment that feels
warmer at a comparably lower space temperature than HVAC systems.
The highly efficient ground source heat pumps transfer heat energy for space heating and generating hot
water. A closed loop system draws warmth from the earth through a series of tubes – or loops – installed in
the ground. As the liquid slowly moves through the tubes, it absorbs heat from the earth where the yearround ground temperature remains about 55 degrees. When the warmed liquid is pumped into the building,
the heat pump extracts and concentrates the heat from the earth-warmed liquid and returns the chilled liquid
to the loops in the ground to repeat the process. Next, the heat gets transferred to a separate system of tubes
and liquid circulating through the radiant floors at mild temperatures, typically up to 90 degrees. This is
lower than temperatures needed for typical HVAC systems, thus requiring less energy.
A second heat pump is used to create higher temperatures for hot water. In a similar process to the space
heating described above, it distributes heat to the domestic water supply and maintains it at a temperature
of around 130 degrees. A backup gas water heater is on-site, but is rarely needed.
Eco-impact:
 Heat pumps are the most efficient heat source in terms of energy input/output.
 Ground source heat pumps have a coefficient of performance (COP) of 3.2, which means they
output 3.2 units of heat for every unit of energy consumed. They are more efficient than the less
expensive air-to-air heat pumps and are 320% more efficient than electric baseboard heat, which
has a thermal efficiency of nearly 100% (meaning nearly every unit of energy is used directly for
hearing). Their operational costs are significantly less than other HVAC systems.
 A gas furnace or water heater could be as low as 80% thermal efficiency, which means for every
100 BTUs of gas consumed only 80 BTUs are used for heating. The rest either does not combust,
or is exhausted as waste heat. The most efficient water heaters are 98%-99% efficient, which is
still much less efficient than heat pumps.
Living Roof and Stormwater Management
A well-insulated roof also plays an important role in keeping the building comfortable. The 21 Acres
Center incorporates a living roof (also called a green roof or eco-roof) – a vegetated roof cover with
growing media and plants taking the place of bare membrane, gravel, shingles or tiles. It includes a
waterproofing layer, drainage mat, growing media and plants covering the surface.
The living roof at 21 Acres offers many benefits in addition to the obvious appeal of growing things. Its
structure and density provide insulation, while extending the life of the roof membrane by protecting it
from UV radiation. Evaporative cooling from the living roof lowers the roof surface temperature during
warmer months, helping to keep the building cool. The plant and soil matrix slows down the flow of water
from the roof during rainy months, and the water that is not absorbed by the plants is guided down to rain
gardens on the site where it can recharge the natural ground water system.
All stormwater is handled on-site via the rain gardens, pervious paving in vehicle traffic areas and
conveyance swales. Rather than being routed to the storm drain system, which exacerbates pollution of our
rivers and oceanwater, stormwater is allowed to slowly infiltrate back into the earth to recharge natural
acquifers.
Eco-impact:
 The living roof reduces the heat island effect and absorbs carbon dioxide.
 The soil and plantings provide a habitat for diverse plant, animal, insect and bird species and serve
as a filtration system for rainwater falling on the roof.
 Infiltration of stormwater on-site helps recharge groundwater.
Rooftop Solar Panels
The remainder of the roof holds a 25.2 kW rooftop photovoltaic (PV) array which generates approximately
25,000 kilowatt hours annually. Power generated by the solar panels that is not used by the 21 Acres Center
is delivered back to the electrical grid through net-metering for an equivalent credit applied to the facility’s
account.
The building is equipped with computerized circuit breakers that measure electrical consumption at the
breaker panel. An energy monitoring system graphically displays daily production and consumption
numbers on a public touch screen kiosk and provides feedback about the effectiveness of the energy saving
features.
Eco-impact:
 The energy produced by the solar array at 21 Acres provides enough power to offset
approximately 15% of the facility’s electric consumption.
 The monitoring system facilitates the building manager’s ability to track how the building uses
energy. If energy use of a particular system increases or declines in an unusual way, it can be a
symptom of a problem or a change in occupant behavior. This system allows the manager to
investigate issues immediately before they show up as large energy bills.
Energy Conservation
To address energy use by occupants inside the building, 21 Acres has incorporated a number of energy
conservation features and technologies that reduce energy use while ensuring that the space remains
comfortable and useful.
Large, well-placed, thermal windows and strategically placed skylights allow ample daylight to enter the
building, even on the darkest winter days. The special skylights are filled with a nanogel that blocks the
heat of UV rays and reduces heat loss during cold temperatures while allowing light to pass through.
Lighting is often a big energy consumer, particularly in commercial buildings, and day-lighting
significantly reduces the demand for lighting. When daylight is not sufficient, high-efficiency light fixtures
are used. Ambient light sensors read available light levels during the day and turn off fixtures when light is
not needed. Occupancy sensors turn off lights in areas that are not occupied.
An 11-horsepower, gearless traction elevator uses approximately 70% less energy than a conventional
hydraulic elevator and uses no hydraulic oil, avoiding the risks of soil and groundwater contamination and
fire.
Cooling and airflow inside the building are managed without the use of conventional air conditioning or
HVAC systems, which are among the most energy-intensive building systems.
Eco-impact:
 The combination of energy conservation features at 21 Acres reduces the facility’s overall energy
use by approximately 24% over a conventional building.
 By reducing the demand for energy, the building’s energy cost reduction is closer to 47%.
Indoor Environment: Air Flow, Water Quality and Acoustics
Buildings are where we spend approximately 90% of our lives. An important metric for a successful green
building is a healthy indoor environment for its occupants. Construction of the 21 Acres Center was
optimized to maintain high indoor environmental quality with fresh, clean, well-circulated air that is
uncontaminated by the off-gassing of toxic chemicals from building materials and finishes. Materials were
selected to minimize potential toxins from paints, glues, fire retardants and surface finishes that collect
dust, mold, dirt and organic material carried in by the air or its occupants. The combination of carefully
selected materials along with the building’s ventilation system discourages the entry of dust, particulates or
other toxins into the indoor environment.
Fresh air enters the building through two large duct openings that penetrate the earthen berm. The ducts,
which are large enough for a human to stand in, temper the air before it enters the building, allowing
entering air to warm in winter and cool in summer. Ultra-quiet, energy-efficient fans draw in large volumes
of fresh air that then passes through a UV lamp unit to kill any bacteria and MERV 13 air filters to remove
particulates. The air is then distributed via ducts in the berm to further temper the air. During the cold
winter season the air can be warmed to room temperatures before entering rooms by passing through heat
exchangers containing water heated by the ground source heat pumps. Fresh air is replenished only when
the space is occupied and reaches preset CO2 levels to minimize loss of space heat as the fresh air supply
exhausts through the building ventilation system.
Water quality for drinking and cooking was also a priority for the 21 Acres Center. Municipal water
typically contains chemicals including chlorine and fluoride. It can also pick up contaminants from the
water source and water distribution systems. Depending on the water usage, 21 Acres employs a one or two
stage filtering process. The first stage, at the water entry point to the building, removes chlorine, organic
chemicals, lead and parasites, which is sufficient for the majority of building uses typically related to
washing (e.g. hands, dishes, equipment). However, water used for consumption, as in food preparation,
cooking, and drinking, goes through a second stage of filtering which removes fluoride, lead, rust, arsenic,
copper, nitrate, sodium, sulfate, chloroform, giardia and cryptosporidum for ultra-pure water. This ensures
that water for consumption at 21 Acres is of the healthiest quality possible and consistent with the
organization’s mission to provide chemical free food.
While acoustics are often overlooked, special attention was focused on maintaining comfortable, efficient
acoustics inside the building’s offices and meeting spaces. Many building projects that elect to minimize
floor and ceiling finishes end up with lots of hard surfaces that can bounce sound around in undesirable
ways. The proprietary ceiling system in the 21 Acres Center combines structural decking with a perforated,
finished ceiling that offers amazing acoustical benefits, minimizing noise and making it easy to hear
someone speaking from across the table or across the room.
Eco-impact:
 While difficult to quantify for the 21 Acres Center specifically, numerous studies have shown that
reducing indoor air pollution from material off-gassing has positive short-term and long-term
effects on the health and well-being of a building’s occupants.
 Fresh air supply is ensured to create a healthy indoor environment, but the system runs only when
the space is occupied to minimize its impact on the building’s energy consumption.
Composting Toilets and Wastewater Systems
The site of the 21 Acres Center posed some unique challenges for handling wastewater. Because it is
situated on a flood plain and above a shallow water table, extra measures were taken to manage wastewater
in an environmentally safe manner.
Like most commercial buildings, potable water enters the 21 Acres Center from a municipal main.
However, unlike most commercial buildings, human waste and wastewater is processed on-site via two
systems. Clivus Multrum® composting toilets are used for human waste. Gray water waste is treated by a
series of Nibbler® bio-digesting tanks located in the earthen berm on the south side of the building and
gravity fed to a Glendon® Bio-filter System located away from the building. Each of these systems mimic
living organisms that breathe air, consume organic material, and, in the process, produce essentially pure
water and inert bio-solids.
Much of the water that is used inside a typical commercial building is used to transport waste from the
restrooms, drinking fountains and washing stations to the public sewer system. To lower water usage in
restrooms and manage wastewater, 21 Acres installed waterless urinals, low-flow fixtures and composting
toilets, which use 95% less water than a typical 1.6 gallon toilet.
The composting toilets use foam rather than water to carry the waste from the bowl to the composting unit,
so very little water is required during each flush. The sloped design of the composting unit uses gravity to
separate liquids from solid waste allowing solids to decompose aerobically. The liquid settles to the bottom
of the composting unit where it is pumped to a storage tank. The nutrient rich liquid can be processed for
plant use. After a period of several years, the remaining bio-solids can be removed and used to fertilize
horticultural plants. The composting toilets otherwise look and operate just like ordinary, odor-free toilets.
Gray water from the building flows through a series of bio-digesting tanks in the berm before entering the
biofilters. The bio-digesting system is specially designed to handle commercial kitchen wastewater,
filtering oils and decomposing solids with a combination of anaerobic and aerobic bacteria prior to sending
the wastewater into the biofilter system.
The biofilter uses no chemicals or disinfectants, ozone or ultraviolet processes. The system, which is
located on the Back 18 behind the 21 Acres Garden Shed, consists of different layers of sand and gravel
placed in a watertight box built into the soil with a sand fill placed over the top of the entire area. Effluent
is pumped into the bottom of the filter and allowed to wick itself up through the sand. The filtering
progresses as the water rises through the layers, and what spills over the rim of the box and into the
surrounding soil is clear water. Any remaining effluent remains under the cover sand.
Eco-impact:
 The composting toilets together with waterless urinals and low flow fixtures reduce water use at
the facility by 85% over conventional fixtures.
 Processing of all gray water and wastewater on-site ensures that water is recycled and filtered
before being returned to the environment.
 Water reduction measures save approximately 38,000 gallons annually, and a total of 46,000
gallons are kept out of the municipal sewer system.
Gardens, Grounds and Parking
Despite the disruption to the site during construction of the 21 Acres Center, more than two-thirds of the
original vegetation was protected or restored. A reduction of the heat island effect was accomplished using
light colored pavers for both the parking and pedestrian surfaces. These small pavers allow runoff to
penetrate and infiltrate downward into the sand and gravel base below. Vegetated bio-swales and rain
gardens adjacent to the pavement also provide filtration of sediments and contaminants in the storm water
runoff draining onto the pavement.
Rounding out the on-site green features are two electric vehicle (EV) charging stations available to all EV
owners. 21 Acres participated in the U.S. Department of Energy’s EV Project.
Eco-impact:
 The walks and driveways at 21 Acres absorb one-third the heat of typical asphalt.
 Approximately 3.7 million gallons of water fall on the site annually. None of that water leaves the
site via the storm drain system – the water either infiltrates, evaporates or is used to recharge a
wetland on the site. From the wetland the water flows underground, eventually draining into the
Sammamish River.
 Promoting the use of electric vehicles helps reduce carbon emissions because EVs emit no tailpipe
pollutants and they operate more efficiently than gasoline-based cars.
 EVs convert about 59-62% of the electrical energy they consume to providing power to the
wheels, whereas conventional gasoline vehicles convert only about 17-21% of the energy stored in
fossil-fuel-based gasoline to power at the wheels, according to the U.S. Department of Energy.
Comfort and Sustainability
The integration of the many building systems and materials utilized at the 21 Acres Center noticeably
affects its level of efficiency and comfort. The green building features help to minimize the facility’s total
energy consumption, make it more sustainable overall, and do so without sacrificing convenience or
comfort for the building’s occupants.