34 • Interface February 2004
Ford Motor Company was at a crossroads in
1999. Discussions were ongoing about what to
do with the aging Rouge Manufacturing
Complex in Dearborn, Michigan – the flagship
of Ford’s worldwide operations. Many observers
predicted it would be abandoned due to old age
and deteriorating infrastructure. After many
internal debates among top management personnel
and several discussions with architect
William McDonough, a leading advocate of “ecoeffective”
design, Bill Ford, Jr. announced a
decision to continue operations at the Rouge.
He challenged Ford engineers to find ways to
make the Ford Rouge Center a model of 21st Century sustainable
Ford planners considered several novel approaches to environmental
challenges at the site. One McDonough proposal, adding a
green roof to a planned assembly plant design, was met with universal
puzzlement. Was this a serious suggestion? No one knew
for sure what a green roof was or what advantages it might bring.
Stormwater management is a major concern at the Rouge.
Most of the 1,100 acres that comprise the site are already built
upon or paved. Adding a green roof to a proposed new assembly
plant was evaluated as an initiative that could aid in minimizing
and cleaning water run-off. It would also help keep the new building
cooler in the summer and add to the lifespan of its roof. The
Figure 2: “Green” roof in autumn.
Figure 1: Ford roof in summer.
February 2004 Interface • 35
green roof could be a noteworthy
focal point of a sitewide
management plan to
include drainage swales,
water storage lagoons,
ponds, and porous pavement
in parking lots.
Making the business
case was another matter.
Obviously, building material
needs would change significantly
with the addition
of water-retaining vegetation
on the roof. Preliminary
cost estimates for a
green roof ranged from two
to three times the price of a
conventional roof system.
As part of an overall site
design, however, the cost of
all proposed stormwater
reduction initiatives was
weighed against the cost of
a traditional stormwater management system consisting of miles
of drainage pipes and a water treatment plant. In that context, the
business case was favorable, and the decision was made to go forward
with the green roof.
Building Materials were Upgraded
Structural steel for the project had to be ordered before roof
planning was completed. A preliminary roof design, based on
sedum plants growing in four inches of topsoil at saturated conditions,
added 25 psf to the original anticipated load. A truss and
design was specified,
and a threeinch
steel roof deck was
called for rather
than a traditional
1.5-inch deck. A
was used with a
top board of perlite
Due to the
potential for water
and root penetrations
to be problematic,
given to selecting
for the vegetation
bitumen system was selected based on performance expectations
and its two-ply design. A Paradiene Tarabase layer covers the
metal deck, and a Teranap waterproofing membrane is placed on
top of that. The combined thickness is 160 mils.
The company supplying the green roof, Xero flor, recommended
a specific root resistant membrane be used in addition to the
waterproofing membrane. The selected product is a 20-mil, highdensity
polyethylene film certified to German FLL standards. (The
FLL is a green roof industry standards testing and certification
organization. The American standards testing counterpart, ASTM,
Figure 3: The components comprising the Xero flor
green roof system.
Figure 4: Procedure for applying polyethylene root barrier, vegetation mat, and substrate sequentially at cultivation
site in Allen Park.
36 • Interface February 2004
is working on an adaptation of the FLL standards
for the American market.)
The Xero flor Green Roof
After devoting development time to creating an
original green roof system, Ford contracted a longestablished
company, Xero flor of Gross Ippener,
Germany, for the project. The Xero flor product is
an extensive green roof system utilizing layers of
lightweight foundation materials, thin substrate,
and vegetation. The saturated weight of the system
is 11 psf, making it significantly lighter than the
design specification of 25 psf. A unique feature of
the system is that the vegetation layer is grown at
ground level and transported to the roof after it has
Typically, Xero flor delivers the ready-to-install
product from its “farm” in Germany. Since Michigan
is not in the local delivery area, an alternate plan was developed
to grow the vegetation blankets near the facility where it was to be
installed. A fifteen-acre, Ford-owned site was selected to be the
cultivation area. Materials, including specialized machinery,
shadecloth, synthetic mats, absorbent fleece, drainage materials,
and sedum seeds were shipped from Germany to Allen Park (near
Dearborn) for the project.
Instead of soil, a growth mixture consisting of expanded shale,
sand, compost, peat, and dolomite was obtained locally and
spread over twelve acres of synthetic materials (see Figure 4).
Distribution of seeds from eleven species of sedum and cuttings
from two additional varieties of sedum was spread randomly over
the twelve-acre plot. An irrigation system and shadecloth were utilized
to keep the young plants moist during the initial growth
period. The vegetation blanket was grown from May to September
2002 and installed in September and October.
Green Roof Installation
One major concern with the green roof installation was that
the transfer from field to roof had to be quick and efficient. The
Figure 5: Green roof membrane application.
Figure 6: Workers position individual squares of sedum on fleece underlayment.
February 2004 Interface • 37
roofing contractor, ChristenDetroit, coordinated efforts with
the grower, Xero flor, to assure that cutting and transport
operations took place sequentially over a four-week period.
The vegetation blankets were cut into 1m x 1m squares,
placed on wooden pallets, and loaded onto flatbed trucks. The
materials were driven to the Rouge and hoisted to the roof by
extension forklift trucks.
Pallets were placed on motorized four-wheel transports at roof
level, and vegetated mats were distributed
to areas to be covered.
Prior to installing the mats, remaining
system materials were rolled
out. These included the root-resistant
membrane, the drainage material,
and the fleece layer. Due to
windy conditions on several days,
the sublayers were thoroughly wetted
down to remain in place (Figure
5). This was also helpful for getting
the vegetation off to a moist start
after some drying occurred during
Placement of the mats on the
roof was similar to installing shingles
on a roof. Pieces were staggered
appropriately with edge
materials butted together (Photo 6).
The mats have a six-inch “flap” that
extends from one side of the
square. This allows each piece to be
overlapped and held in place by the
square next to it.
As the vegetation blanket was placed on each section of the
roof, that portion of the roof’s irrigation system was installed. The
plants were watered on a daily basis for the first couple of weeks
Below: Figure 8: Flowering plants on the roof.
Left: Figure 7: Roof-dwelling birds (kildeer) appeared during
the spring of 2003.
Figure 9: Aerial view of new assembly plant and green roof.
GREEN BUILDING CO$T
The state of California recently published a study comparing
the cost of 40 green buildings (most of them LEED certified)
to conventional buildings. They determined that, on
average, the initial costs of green buildings were only 2%
higher, and the long-term benefit-to-cost ratio was 10 to 1.
— Grist Magazine
38 • Interface February 2004
after being transferred to the roof. During 2003, the irrigation system
was used on an as-needed basis as the vegetation filled in.
Plans are for it to be used sparingly in 2004 and possibly discontinued
altogether after plant establishment is complete.
Maintenance activities during the first year were minimal.
Because the plant coverage was approximately 70% shortly after
installation, some vegetated areas were subject to weed infiltration.
Weeding was performed periodically during the first summer
and tapered off as sedum coverage increased. It is anticipated that
weed removal will be a maintenance item in the second year,
although to a lesser extent than in the first year.
Mowing is not required. The sedum selected for this installation
is a low-growing variety that tends to propagate horizontally
rather than vertically. To replenish lost nutrients in the substrate,
a slow-release fertilizer application is planned each spring.
Green roof benefits are varied and not always obvious. Extending
the life of the roof by minimizing expansion and contraction
effects is predictable. Cooling the building interior in summer is
an understandable benefit as well. Stormwater reduction and
water cleansing advantages are notable as compared to a conventional
roof. For the Rouge, however, bringing back wildlife to the
site is a welcome change. Birds and butterflies are finding refuge
on the roof (Figures 7 and 8), and workers are excited about the
prospect of improving the environment that they work in and
around every day. At 10.4 acres, the world’s largest living roof has
finally gotten off the ground. Hopefully it will benefit everyone at
the Ford Rouge Center and become a blueprint for future industrial
green roofs in North America. ■
Donald K. Russell is manufacturing
sustainability manager for the
Environmental Quality Office of Ford
Motor Company. For the past three
years, he has been part of the Rouge
Heritage Team evaluating environmental
initiatives for the Ford Rouge
Center. His recent projects include
the green roof at the new Dearborn
Truck Plant and a phytoremediation
research study to identify plants
capable of cleaning contaminants
ABOUT THE AUTHOR
DONALD K. RUSSELL
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