<1
\ Office of Administration
& and Resources Management
Vital Statistics
Facility Type: Office
Construction: Leased/New Construction
Location: Denver, Colorado
Size: 314,200 gross square feet (partially
occupied by EPA)
Opened: January 2007
LEED© Status: Gold for New
Construction (version 2.1)
LEED Points Earned: 40 of 69 possible
EPA's Region 8 Office was built as a. demonstration project of the General
Services Administration's (GSA's) Office of Federal High-Performance Green
Buildings. This "build-to-suit" office and retail space was designed and
constructed through a. design-build public-prwate partnership to be as sustainable as
technology and budget would allow, incorporatingsustainabilty elements developed
jointly by GSA and EPA. The building now stands as a hallmark of erw iron mental
sustain ability in Derwer's Lower Downtown Historic District. Since the Region 8
Office opened in 2007, one of its most successful sustainablefeatures has been the
vegetated or "green" roof, the first of its kind in Colorado.
Studying a Groundbreaking Green Roof
The green roof at the Region 8 Office, which is ENERGY STAR© certified, consists
of plants growing in trays made of recycled plastic, which cover 20,000 square feet
(nearly 60 percent) of the 35,000-square-foot total roof surface of the tiered 8th, 9th,
and 10th floors. When first installed, the trays contained 40,000 individual plants
rooted in 4 inches of soil. Four species of sedurn were selected for visual appeal,
survivability in harsh environments with temperature extremes, and for their capacity
t. o wit hstan d drou ght c o ndit i ons.
A team of EPA researchers from Region 8 and EPA's Office of Research and
Development's National Risk Management Research Laboratory led a series
of research studies to address the numerous challenges faced by the green
roof—limited natural precipitation, increased solar radiation, high wind velocities,
predominately sunny days, and a thin layer of soil. The research team collaborated
with partners from Colorado State University's (CSU's) Department of Horticulture and
Landscape Architecture, the Denver Botanic Gardens, the Urban Drainage and Flood
Control District (UDFCD), the Alliance for Sustainable Colorado, and the City of Derwer.
EPA dedicated 2,000 square feet of the green roof to conduct research on eight
additional species, six of which are native to Colorado.
Office Green Roof
Sustainable Facilities at EPA / Denver, Colorado / Region 8

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Overcoming Green Roof Growing Pains
An extensive green roof has a shallow growing medium with a modest roof load,
limited plant diversity, minimal watering requirements, and is often not accessible.
Due to the porous and well-drained nature of the typical soil used in extensive green
roofs, the success or failure of the system depends on a species' ability to grow
in the medium. This challenge is exacerbated for extensive green roofs in areas
characterized by high elevation and a semi-arid climate. Over time, the original
plantings of solely sedum species proved less than ideal for the local climate.
Accordingly, the best approach for a green roof in the Denver area was to feature an
array of plants that are adaptable to dry, porous soils. Furthermore, choosing diverse
plant species can provide habitat for birds and insects in urban areas.
The green roof was originally equipped with a drip irrigation system. However,
because the drip lines were placed on top of the trays instead of within the
subsurface, the exposure to sunlight caused them to degrade. Researchers also
suspected that the soil did not allow for water to spread laterally across the trays,
which limited the growth of the plants. As a result, the drip system was replaced with
a spray irrigation system in 2009,
The research team confirmed that watering practices should reflect seasonal
conditions. Spring irrigation in March, April, and May might not be necessary,
depending upon the amount of natural rainfall and the ambient temperature. In
contrast, the summer months are the most crucial months for irrigation. Winter
watering can be useful for maintaining healthy plants during warmer, dry periods.
However, in seasons where regular snowfall is accumulating and melting on the green
roof, winter watering is not necessary, in very dry years, watering can help prevent
plant loss due to desiccation.
Notably, shading beneath or at the edge of the solar photovoltaic panels can produce
a synergy with the green roof substrate, keeping the area cooler and requiring less
irrigation.
Urban Heat Island
A "heat island" is an urban area that experiences higher temperatures than nearby
rural areas. The annual mean air temperature of a city with 1 million people or more
can be 1.8 to 5.4 degrees Fahrenheit warmer than its rural surroundings. In the
evening, the temperature differences can be as high as 22 degrees Fahrenheit, Heat
islands affect communities by increasing summertime peak energy demand; air
conditioning costs; air pollution and greenhouse gas emissions; heat-related illness
and mortality; and water quality.
Stormwater Management
When the Region 8 Office was designed,
mitigating stormwater runoff with green
roofs was a non-standard practice.
Therefore, the building developer had to
provide significant data up front without
reasonable assurances that the project
would be approved by the local drainage
district, UDFCD, or prove effective in
its designed purpose—detention and
infiltration of stormwater.
Stormwater performance data collected
from the green roof and compared to a
conventional, gravel roof on a building
across the street from the Region 8 Office
supported the hypothesis that the green
roof is effective at detaining and infiltrating
stormwater runoff. This is especially
tnie for snowmelt events and for smaller
precipitation events (generally less than 1
inch of rainfall in a 24-hour period).
Data from the Region 8 Office project was
used to establish the installation of green
roofs as an approved best management
practice for infiltrating and detaining runoff
by UDFCD. Developers can now choose
to install a green roof without additional
analysis, using design specifications and
performance criteria provided directly by
UDFCD.

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Under the Roof: Energy-
Efficient Design
Beyond reducing the uifcan heat island
effect with its green roof, the building's
integrative energy-saving design features:
•	Forty-eight solar photovoltaic (PV) panels
with peak output of 10 kilowatts.
•	High-efficiency window glazing, external
shading and interior light shelves,
daylight and occupancy sensors, and
reduced power use for lighting based on
open workspace floor plans.
•	Improved heating, ventilation, and air
conditioning design parameters and
equipment efficiency, variable frequency
drive chillers, underfloor air distribution,
and an air-side economizer.
•	Increased insulation in walls (R19) and
roofing (R31).
The building's two "L" shaped wings with
a central atrium maximize daylighting and
allow building managers to take advantage
of local environmental conditions in
operating the building. The temperature
and lighting can be adjusted to balance
comfort levels in each "L" based on ambient
daylighting and heat gain conditions. The
central atrium helps reduce energy use
because it is a partially conditioned space
that acts as a thermal buffer for the building
as a whole.
Green roofs can mitigate the heat island effect by providing shade and removing heat
from the air through evapotrans pi ration. When compared to a conventional, gravel
roof on a building across the street, the temperatures on the Region 8 Office's green
roof were lower during hot weather and higher during cold weather. The cooling and
warming properties of the green roof derive from the retention of moisture in the
green roof's plants and growing medium.
Because temperatures on the green roof are less extreme than those of the
conventional roof, the green roof waterproof membrane suffers less physical
stress. This may explain why green roofs can last two to three times longer than
a conventional roof. Not having to re-roof as frequently lowers the amount of
construction debris generated and saves money on roof maintenance.
Lessons Learned
Research with CSU and an evaluation by a green roof expert revealed the following
lessons from the green roof installation at the Region 8 Office. These lessons can
educate others in the best approach for designing green roofs in the semi-arid and
arid West.
•	Plants are more vulnerable to temperature fluctuations when soil depth is 2 inches
or less. Soil depth should be at least 4 inches to support evapotranspiration, which
helps maintain a constant temperature across the green roof.
•	Plants can die from intense ultraviolet (UV) and hot temperatures from the plastic
tray edges. In addition, exposed irrigation lines are subject to degradation from UV
rays.
•	When the winter turns unseasonably warm, it can send a signal to plants to end
their dormancy cycle. Should this signal occur during freezing temperatures, plants
become more susceptible to die-back.
•	In the fall, cut back dead flower heads and stems. During the following spring,
seeds should be shaken out of their seed pods onto the green roof to encourage
the germination of new plants.
•	Reflective heat from windows and metal siding inhibits plant growth. Thus, cacti
should be planted in areas with the highest reflective heat.
•	Scouring from strong winds is the main cause of soil loss; parapet walls help
prevent wind scour.
•	Winter watering should be done during periods of low precipitation.
The Region 8 Office's green roof can help guide the design of future green roofs
in semi-arid climates. The University of Colorado at Denver, working with EPA staff
and UDFCD, developed a comprehensive resource called Design Guidelines and
Maintenance Manual for Green Roofs in the Semi-Arid and Arid West. Using these
guidelines and standard software for modeling stormwater runoff reductions,
developers can design, construct, and access the many benefits of green roofs.
Contact Information:
United States Environmental Protection Agency
1200 Pennsylvania Avenue, NW Washington, DC 20460
August 2017
EPA 908 F 017 002

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