Anchorage Daily News

For nearly 30 years, master gardener Marnie Isaacs' roof has been her lawn.

It has also been her garden.

Above her ceiling, tomatoes ripen on the vine and a horde of raspberry bushes is straining to escape a fenced, raised bed.

Isaacs and her husband, Jon, don't have to scale the walls to get to the greenery: Their home is mainly underground.

Witness a tried-and-true Alaska green roof.

These days, a passion for "green" roofs -- roofs covered with vegetation -- is taking root in North American cities such as Chicago, Seattle and Toronto, where city leaders are using them to combat urban blight and pollution.

Though they aren't common in Anchorage, green roofs certainly aren't new here. The Isaacs' roof has been sprouting in Turnagain for decades. And one of the city's most attractive buildings is the Anchorage Convention & Visitors Bureau's sod-roofed log cabin in the middle of downtown.

Green roofs aren't new to Alaska. The ultimate green roofs, perhaps, grew naturally on the traditional sod homes of the Arctic.

TRENDY TOPS

But the new wave of green roofs catching hold Outside and in Europe doesn't look anything like a traditional sod dwelling.

These newfangled "extensive" green roofs originated in Europe. The roofing plants are usually able to live comfortably without watering or fertilization. The intent is to trap storm water, filter water and air pollutants, improve urban aesthetics and cool the ambient air.

These roofs often involve installing interlocking plastic containers or mats filled with plants. The plants sit on top of a waterproof liner, a water drainage layer and possibly a fabric layer serving as a root barrier.

The vegetated mats or shallow containers are usually filled with shallow-rooted, hardy plants, especially sedum.

Typically, these roofs are installed on commercial and government buildings, but they also flourish on single-family homes.

Not all modern green roofs are planted with shallow-rooted plants. If a building can support the weight, trees, vegetables and other deep-rooted plants can also go on a green roof. But these roofs cost more and require irrigation and fertilization.

COLD EXPERIMENT

This summer, some Anchorage architects and landscape designers are trying to figure out if they can get more green roofs established in Alaska.

Because of Alaska's colder climate, these roofs probably won't look a whole lot like those in the Lower 48 or Europe.

For example, there's the new partial green roof at Denali National Park's new Eielson Visitor Center. The roof, installed in May, features patches of native tundra removed from the construction site.

On the Anchorage Hillside, a local firm, Black and White Studio Architects, is finalizing plans for a green roof at a new house.

Like the Isaacs home, this one will also be partially submerged in the ground, said Bruce Williams, the principal architect.

The roof will include places to sit and walk. The soil will be deep enough -- about eight inches -- to grow vegetables and flowers, he said.

"It's going to be pretty cool," he said.

"We've taken the landscape and put it over the house," he said.

A green roof can't just be installed willy-nilly, of course.

For example, to support all that additional weight, the roof on the Hillside home has been designed to support an additional 20 pounds per square foot over the 55 pounds that is normal for Alaska roofs, Williams said.

The plants -- probably a combination of wild grasses and wildflowers -- will be planted in trays with a waterproof layer and drainage system underneath, he said.

Roofs that are used to grow flowers, trees and other plants are termed "intensive." While they are potentially more attractive and useful, they can be a lot more costly.

GREEN WALLS

If a green roof sounds like too much trouble, a green wall might be an option.

Green walls are often built indoors, and Anchorage already has at least one.

Erma MacMillan, a sales manager at the Green Connection nursery, hired a California firm that specializes in green walls to install a vertical wall of ivy at the nursery this spring. The project cost about $135 per square foot, including labor, she said.

She sees the ivy, which frames a doorway on an interior wall, as "horticultural therapy."

The ivy grows from a series of shallow trays installed flush against each other so it looks like a continuous blanket of plants. The plants are secured in specially designed mats and a soil medium that resists erosion.

The nursery's green wall has its own watering system. An organic fertilizer helped get the plants growing.

"So far, it's worked great," MacMillan said.

---

Find Elizabeth Bluemink online at adn.com/contact/ebluemink or call 257-4317.

---

A primer on green roofs

WHAT'S A GREEN ROOF?

It's a roof that has been planted with vegetation. The concept is thousands of years old and not new to Alaska. Think traditional sod houses in the Arctic, as well as pioneer homes.

WHY PLANT ONE?

• You like the idea of lush greenery sprouting from your roof.

• To reduce the quantity of storm water runoff, allowing rainfall to replenish the local aquifer; also, to filter impurities from storm water, which ultimately reduces water treatment costs.

• To lower indoor temperature in summer.

• To provide wildlife habitat or grow food.

WHAT'S THE DOWNSIDE?

• It's not as simple as just planting a garden -- many plants are unsuitable for a roof because of extensive root systems and nutritional needs.

• You need to do a structural analysis first to ensure that the green roof doesn't overload your home's support structure.

• All components of the green roof need to be carefully selected and installed. The basic ingredients of a modern green roof include a waterproof base layer, a roof protection layer, inorganic soil and a drainage system.

• If you ever need to remove or inspect your roof, you are also going to have to remove a lot of plants and material.

WHAT ARE THE PERKS?

• Installing a green roof is one way for a building owner or operator to get a high environmental ranking from the U.S. Green Buildings Council, under its Leadership in Energy and Environmental Design Initiative.

• Some states (not Alaska) offer tax incentives for including green roofs or other eco-friendly building practices in the design of new commercial buildings.

GREEN ROOF TRIVIA

• A 2005 university study commissioned by the city of Toronto found that if all suitable roof space in the city were converted to green roofs, the city would save about $37 million per year, primarily in reduced energy costs.

• In summer, depending on the plants and depth of soil, green roofs retain 70 to 90 percent of the precipitation that falls on them.

• An installed green roof with root-repelling and waterproof layers costs $10 to $24 per square foot.

Source: Green Roofs for Healthy Cities

---

ON THE WEB

• Green Roofs for Healthy Cities:

greenroofs.org

• Green roofs in Seattle (click on "City Green Building"):

seattle.gov/dpd/planning

• U.S. Green Building Council:

www.usgbc.org

ADVERTISEMENT