Music City Center trims green roof plan The Tennessean

Music City Center trims green roof plan The Tennessean

Project still will make statement

Two pieces of the meadow-like expanse have been sliced from the design to stay within the project’s $585 million budget.

That still leaves about 178,000 square feet of greenery covering 28 percent of the 14.5-acre roof.

While that’s considerably less than several of the living roofs across the country, it appears to be the largest such undertaking in the Southeast so far, according to the industry group Green Roofs for Healthy Cities .

It’s an appreciable amount of space, and it’s great they’ve adopted a green roof, said Councilman Mike Jameson, a self-declared greenie whose district will include the center.

I would like it to be more ambitious, and the initial design rendering was more ambitious.

He voted with a small minority against building the 1.2-million-square-foot convention center now under construction behind the Bridgestone Arena. He had called for full sustainable features if it were approved.

The green roof’s benefits include capturing stormwater, which will reduce area flooding and provide water for irrigation and flushing the center’s 500 toilets. It also will cut energy costs and help clean the air. But designers are focused on the statement that a major green building can make.

All the sustainable components that go into it really say that Nashville has made a commitment to make sustainable public buildings, said Paul McKeever, an architect on the project with tvsdesign of Atlanta.

The green roof is definitely one of the more visible elements of that.

Jameson said the original concept with a larger green roof would probably have paid for itself in the years ahead and made a better investment for the community.

That’s an unknown, according to the Nashville Convention Center Authority, which will oversee the Music City Center.

No estimates are available on what the savings might be with this or the originally conceived green roof, said Holly McCall, an authority spokeswoman.

As far as the green roof is concerned, the energy model for the roof has not been completed, so we can’t really give an estimate of savings at this time, she said in an e-mail.

Aside from any savings, going green is just the right thing to do, she said.

Plus, Metro requires new city buildings to win silver certification in the environmental LEED program. The Music City Center will meet the minimum, but a higher level with more eco-features would cost more.

Information about the possible price tag on the Nashville roof project can’t be released until the contract is awarded to a bidder, McCall said. That is expected in a few weeks.

Green roofs of the low-maintenance type planned here generally can cost about $10-$25 a square foot, depending on the size. With installation added, that could put the Nashville convention center’s green roof at $2 million or more.

The greenery is expected to extend the life — maybe by double — of the roofing over the portion where it lies.

It also has a structural function. The green addition will weigh in at up to 21 pounds per square foot, depending on whether it’s wet or dry. That’s as much as 3.7 million pounds.

The heft will provide ballast over trusses between exhibit halls below to combat wind uplift on the wide-brimmed roof.

Green roofs common

Green roofs date back at least to the Hanging Gardens of Babylon in 600 B.C. and today they’re commonplace in Germany and other parts of Europe. That’s becoming the case also in North America.

Some cities, including Toronto and Chicago, require green roofs on new buildings over a certain size. New York City and Philadelphia are among places with tax incentives to build them.

Cities are seeing rooftops as a way of delivering infrastructure benefits to the citizens, said Steven Peck, president of Green Roofs for Healthy Cities.

The federal government builds with green roofs and has 35 so far, with the oldest built in 1975 in Portland, Ore. They’re found on U.S. courthouses, federal office buildings and parking garages, with examples in Atlanta and Birmingham, Ala.

Nashville has at least 10 green roofs on government and commercial buildings, with one being the Public Square Park, above the underground parking garage at the Metro Courthouse. Those in Williamson County include one at Nissan USA and one at the Franklin Police station.

"Green roofs aren’t just about the buildings — they’re kind of a statement of greenness and progressiveness of the city," Peck said. "It says this is a green building. It’s giving back to the city, helping clean the air, helping cool, providing habitat for birds and nature."

That statement can go unnoticed if people aren’t able to see the roof.

In the case of the Music City Center, the vegetated roof can’t be viewed from the street, but it will be visible from several tall buildings, and a window is included inside the center to look out at it. The roof itself won’t be open for walking around.

The Target Center arena in Minneapolis, which looks like a roundish leaf from above, is providing an iconic image of the city, Peck said, and it’s seen only from other buildings and the air.

Every time you see an aerial shot of the city, the Target Center jumps out at you, he said. There’s a huge leaf in the middle of the city.

Sedum stores water

The Music City Center roof will not be a showy garden of tall flowers, trees and shrubs. The plants are mostly business. They’ll be hardy, low-lying sedum with fat, water-storing leaves that give them the ability to withstand drought.

The living part of the roof should provide a slow-motion kaleidoscope of soft colors as the different types of sedum — with names such as blue spruce, hens and chicks, and iceplant — flourish at different times of the year. Burgundy in fall will change to green in spring, and tiny red and yellow flowers will appear in summer.

Music City Center trims green roof plan The Tennessean

They’ll grow in 3-4 inches of a soil substitute made with shale bits that have been cooked until they explode like popcorn and are light with tiny crevices.

The roof system is laid out in layers like a sandwich, with a membrane to protect the building, a filter and a water collection system that will send excess water to a 300,000-gallon tank under Fifth Avenue North and Demonbreun Street for reuse. That saves the cost and unnecessary use of the city’s cleaned and chlorinated drinking water to flush toilets and water plants.

If someone thinks a green roof is no maintenance, they’re wrong, said Andy Sudbrock, owner of Southeast Green Roofs and Nashville Natives in Fairview, which provides plants for green roofs.

His company is one of two — the other is the Dutch-owned Sempergreen — that are part of roofing bids for the Music City Center project.

The care includes taking a walk over the greenery every few weeks to see whether any weeds need pulling. The sedum can handle being trod on, but not heavy traffic like in a park. The area will be lightly mowed every year or two also, with the snipped bits able to sprout threadlike roots and grow.

Sedums love it, Sudbrock said. The more you cut the sedum, the more pieces fall and root.

Sudbrock stood last week beside a series of sedum-dappled trays that lay on the ground in the bitter cold, the plants displaying their toughness.

You don’t baby it, he said. You make sure it can survive.

The plants, which will remain in the trays, will be transported in a few weeks and placed on top of a new performing arts center in Carmel, Ind. for a 3,000-square-foot green roof.

The Sempergreen system grows its sedum similar to the way a sod farm produces lawns. The company cuts the sod where the plants grow and rolls the surface into mats that are shipped out. Nashville’s would come from its USA headquarters in Virginia, which furnished plant mats for the 113,000-square-foot Target Center roof.

Maintenance required

A green roof could be an image builder or, if the plants died or the roof leaked, an embarrassment.

"Like any technology, there can be lots of problems if they get people in there that don’t know what they’re doing — that don’t have a lot of experience," Peck said.

The membrane that protects the building must be properly sealed, for instance, and the plants maintained.

The main architectural firm, tvsdesign, hired a green roof consultant because of the size and complexity of the roof, which will have a rolling surface like the hills of Middle Tennessee.

The Nashville contract requires an extensive warranty on the plants and roof, and maintenance ultimately will be up to the convention center authority.

Project Manager Patrick Holcombe said he and his team have great confidence in the technology and the roof that will result.

We want to be able to sleep at night, he said.

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