Facility Retrofit: Green Roof Revisit

By David Aquilina
Published in the October 2014 issue of Today’s Facility Manager

When the Ford Motor Company decided to renovate the Rouge [in the 1990s], what was the status of auto manufacturing at the complex?
At the time, the auto industry, like many manufacturers, was turning away from its historic industrial facilities and factories. It was an era of downsizing and decentralizing. By 1992, the Mustang was the only car still built at the Rouge. Ford and the UAW hammered out an agreement to modernize and maintain vehicle manufacturing at the Rouge in 1997.

As part of this, Bill Ford, Jr., great-grandson of Henry Ford, was keen on demonstrating that environmental improvements can be smart business with cost-effective solutions that are worthwhile investments. In 1999, Bill Ford announced the appointment of the architect William McDonough to design the sustainability plan to bring that vision into reality.

Managing stormwater was essential for the renovation of the Rouge to proceed. Can you summarize the problem?
Henry Ford selected the site because one of its main advantages was access to the rivers for shipping. But, it is low-lying land, and the Rouge was built on multitudes of wooden pilings. Over the years, it was paved over with impervious surfaces. The two main box culverts running through the complex also drain part of the City of Dearborn to the Rouge River. As the city and the complex both grew, more of the area was paved over. Runoff increased, and the infrastructure just did not have sufficient capacity.

So flooding was the problem, especially flooding in the buildings during very heavy rains. If Ford was going to maintain manufacturing at the Rouge, we needed to control and treat the stormwater.

William McDonough conceived the design of a comprehensive landscaped system to manage stormwater. Can you describe the system?
The system encompasses 100 acres of sustainable landscaping. It includes the 10.4 acre green roof on the truck plant, a 16 acre porous pavement storage lot for trucks coming off the assembly line, more than a dozen hedgerows and bio-swales, stormwater ponds and treatment wetlands at several locations, and native and sustainable plantings along the roadways.

Ford's Dearborn, MI manufacturing complex.
Upon completion in 1928, Ford’s Dearborn, MI manufacturing complex featured 93 buildings with more than 15 million square feet of total floor space. (Photo: Xero Flor.)

At the time, what was the fundamental challenge in finding a green roof system?
Remember that this was back in 2000. The various measures Bill McDonough suggested to the project team did not have that much of a track record at the time, especially at the scale we would be applying them. That was the case with the green roof. At the time, there was no green roof industry to speak of—or even very many studies on green roof installations—in the United States. That is why we ended up going to Germany.

[In Germany,] most of the green roofs we visited were plant-in-place systems with 4″ to 6″ inches of growing medium planted with plugs that fill in over time. However, because of the vast area to be covered, we needed a lighter weight alternative to reduce the structural loading of the building. We were also concerned with a plant-in-place system about the risk of leaving so large a surface area of soil, more than 10 acres, exposed to erosion and weed encroachment while the plants grew in over several years.

The attributes we were looking for included the essential considerations that go into evaluating alternatives for many green roof projects today: lightweight, ease of installation, minimal long-term maintenance, an instant green roof installed with full-grown plants, and proven performance.

What system was selected?
We selected the Xero Flor Green Roof System. Originally engineered in Germany, it was the available system at the time we thought would work best. At that point, it had been in use for about 30 years, and that was reassuring.

It is a pre-vegetated mat system. The mats are thin and light. The specific option we selected is installed with 1.25″ of growing medium integrated into the mats, and it weighs less than 10 pounds per square foot when fully saturated with rainwater. The mats are pre-cultivated on the ground. They go up on the roof with full-grown, mature plants and 90%+ plant coverage. Overall, the roof has performed so well that Ford installed the same system in 2012 for the 3,465 square foot area atop a portion of our world headquarters building.

How effectively does the overall landscaped system control stormwater?
It is very effective. It takes 48 hours for a drop of stormwater to flow through the landscaped system. It captures and treats stormwater for a once in 10 year, 24 hour storm (about 3″ to 4″ of rain) and achieves flood protection for up to a once in a century, 24 hour storm (about 5″ of rain). It reduces total suspended solids in the stormwater by 85%.

The region’s average yearly rainfall totals 31″, and the green roof itself retains more than 4.3 million gallons of runoff annually.

What are the maintenance requirements?
We have had the same maintenance routine in place for a decade. The roof is fertilized each spring. We check for weeds once a year. That is a main advantage of thin pre-vegetative mats installed without several additional inches of growing medium. This design minimizes weed encroachment because it is difficult for weeds to take hold in a very thin layer of growing medium.

As a sort of insurance policy, we put in a commercial irrigation system when we installed the green roof. It uses the industrial mill water system that exists through the site for manufacturing process cooling. We used it regularly during the first growing season. In subsequent summers, the roof has been irrigated only about once a month during especially hot, dry spells.

What is the condition of the green roof today?
The original pre-vegetated mats retain a very healthy appearance with a dynamic mix of plant varieties. The most recent plant coverage study, conducted in 2010, found that 13 of the 15 original species were thriving with 93% to 98% coverage of hearty vegetation thriving across the roof.

I am still surprised by the variety of wildlife that has found a home up there. Killdeers and other birds nest on the roof. Butterflies, dragonflies and bees are there in abundance. We have a habitat for wildlife right in the middle of an industrial complex.

What lessons learned do you consider most important?
This green roof proved that a thin mat system, weighing only eight to nine pounds per square foot fully saturated, is practical and effective for a large-scale installation. We learned that a mat system with a thin layer of growing medium can be maintained without a great deal of routine attention. We’ve demonstrated that a landscaped alternative for stormwater management including a pre-vegetated mat green roof can be successful.

Aquilina is a business communications professional with experience writing on a variety of business topics. To learn more about Ford’s Rouge plant, visit www.thehenryford.org. For more on Xero Flor, visit www.xeroflora.com.


  1. I’m happy to report that this week I had the pleasure of speaking with both Roger Gaudette, director of engineering, and an original member Ford’s green roof design team, as well as Jack Murray, Ford’s EQO engineer directly responsible for the green roof. The Ford green roof has not been replaced – not once. Furthermore, besides natural rainfall, it has not been irrigated in the past three years. According to Ford representatives I spoke to this week, Ford is happy with their green roof and more importantly pleased that it is achieving the desired stormwater management goals. Sorry Jorg, you have been terribly misinformed. Please retract the incorrect information below.

    Furthermore, Clayton Rugh, PhD, Xero Flor America has posted a detailed summary of the Ford project refuting your comment. Please see discussion at:


  2. Great article and with excellent background information about this amazing Green Roof project. In my opinion, some items seem very misleading for facility managers and building owners.
    The mentioned Green Roof set up at Ford on the Rough can’t retain the amounts of water mentioned in the article. Actually, from my professional view and almost 35 years installing Green Roof in Germany and the US there are serious doubts that it is a good investment for stromwater retention. The system is irrigated – the system must be irrigated to thrive the plants. This artificial water supply reduces the amount of water that can be retained in a storm event, as thunderstorms in summer come very sudden and even highly sophisticates irrigation systems can’t sense that.
    Furthermore the system is so shallow that just by physics the water retention must be substantially lower than on a 4-5 inch extensive Green Roofs, which doesn’t require artificial irrigation (that’s why in the US and in Germany the best ROI is at around 4-5 inch depth).
    The operational costs of such thin layered systems are much higher (based on the irrigation) while the initial costs might be slightly lower when the irrigation system is not put into the calculation. The threshold from initial investment and operational cost is approximately at 3-5 years. In other words and at this point, the Green Roof at Ford Motor Company reduces their profit consistently and more that an extensive Green Roof system with 4 to 5 inch overall depth.
    A year before the install in the US as I toured Green Roofs with a Ford delegation on the engine factory of Mercedes in Germany (around 250,000 sf) it was impossible to demonstrate that 10 times lower initial costs combined with experienced Green Roof Architects and German trained Green Roof Professionals can substantially increase the ROI.
    A year later I consulted Mr. Wolfgang Berhrens (owner and inventor of XeroFlor GmbH) while he was showing me the production of the mats onsite in Detroit. In my opinion, the plants could have been grown directly on the roof for a fraction of the costs and in a deeper system. However, it seemed more lucrative and with less questions by doing things as they were done.
    My take-off from this project was that short and long-term ROI of US based companies is not relevant when CEOs have a vision in mind (big difference to Germany). Maybe this is one reason why Mercedes has over 15 Million sf of Green Roofs on their facilities and a consistently a higher profit over the last 10 years than the much bigger Ford company.
    Things can be done right –or at least much better- from the beginning and will continue to grow from there. How many Green Roofs did Ford install after this project and why not more of the same caliber?

Comments are closed.