Greening the roof

Sandra Ruthven’s garage roof is the ideal poster child for the environment.

Remodeled and installed with a low-water, low-soil rooftop garden a year ago, it’s now a colorful ecosystem in the sky, attracting bees, hummingbirds and the neighbors’ admiration – oh, and a few annoying baby tree seedlings. Overall, though, it’s been an impressive success, and a learning experience for Ruthven and her family.

“It’s been great,” says Ruthven, who designed and installed the roof with her daughter Jenny, then a horticulture student and now a professional roof designer. “It’s a good test roof.”

With some 60 varieties of plants, the roof is a true testing ground. Some plants didn’t make it through the cold winter or the dry summer – the lithodora, the mondo grass, the blue spruce sedum. Some of the thymes didn’t do so well either, which was a surprise. And the north side of the roof, which caught all of last winter’s snow, isn’t as lush as the south.

Overall, however, the roof looks beautiful: a patchwork quilt of reds, oranges, yellows, lime-greens and browns. The red heuchera and pink-flowered bee balm are soaring 2 feet high, attracting bees. A ground-cover euphorbia has cascaded over the gutter; other super performers include sedums, candytuft and oregano.

And there’s surprisingly little maintenance to be done, says Ruthven, who gets up there three or four times a year, mostly to pull out baby trees that have blown in. She doesn’t prune (“You’re supposed to leave it all up there, because that’s the only way it’ll gain humus,” she explains) and turns on the soaker hose for 15 minutes every other day. (A green roof planted only with sedums would need water only once a week.)

Ruthven’s 441-square-foot green roof is the result of several weekends’ worth of work. After tearing off the shingles and bolstering the roof’s support, she and four other friends worked all day to install the framework of felt, waterproof membrane, a grid of Trex supports and a Z-pattern soaker hose. (The full process can be found at A soil-less pumice mix was hauled up, and planting began: one plant per square foot, which Ruthven had previously laid out in a pattern on the ground.

The project cost was $4.19 per square foot, though to have a professional company install it for you can cost up to $12 per square foot, plus any roof reconstruction costs. (The roof has to be strong enough to support the weight.)

Now, Ruthven gets to enjoy the benefits.

“The biggest benefit is stormwater management,” she says. “Instead of flowing right off and adding to the problem of taking pollutants into Puget Sound, we just get a trickle, and even that drains more gradually.” In places like Portland, Ruthven points out, cities actually offer green roof building incentives precisely to effect this kind of solution to stormwater issues.

The garage also stays cool, says Ruthven, cutting the need for insulation. The neighbors are complimentary. And some plants look even better on a roof – small bulbs look cute and the kinnikinnick blooms are more visible from below.

Would she do anything different next time?

“When I made a green roof for my mother, I did an actual design, with only 25 varieties of plant in sweeping patterns,” Ruthven says. “I think that makes more of a statement.”

Interested in doing a green roof? Sandra and Jenny Ruthven will be teaching a free green roofing class next month at the City of Tacoma Envirohouse.

Rosemary Ponnekanti: 253-597-8568

Learn how to Green your Roof

What: Green roofing class taught by Sandra and Jenny Ruthven.

When: 10:30 a.m. Aug. 20.

Where: Envirohouse, Tacoma Landfill, 3510 S. Mullen St., Tacoma.

Cost: Free.

Registration: 253-573-2426,