Mukilteo pulls off City Hall’s weed-filled sod roof

MUKILTEO — The green roof atop City Hall is leaving some people red-faced.

Work crews this week, using a vacuum truck, began removing a weed-infested environmentally friendly roof above the year old, $9 million City Hall’s council chambers.

The roof consists of a layer of soil with native plants and grass.

Roofs like this mimic the way plants and soil absorb and filter rainwater naturally, reducing the volume of storm-water runoff. One is being used for the Winter Olympics expansion of the downtown Convention Center in Vancouver, B.C.

The vegetation roofs also provide insulation from extremes of cold and heat, which saves energy.

Problems were apparent by May, Mukilteo public works director Larry Waters said.

“We didn’t get what we paid for,” Waters said. “Half of it looks green, it’s just not a real green roof. It’s a Charlie Brown weed patch.”

By then, it was clear that subcontractors had mistakenly added mulch full of weeds and alfalfa, which overtook natural ground-cover plants — such as sedum — specifically added for insulation and to control storm-water runoff.

“We’ve been working with the contractor for months trying to figure out how to deal with it,” he said. “It’s a first time for us — we’re not exactly experts on dealing with green roofs.”

Contractor Sierra Construction of Woodinville will pay for replacing the roof, Waters said.

Sharon Collman, a horticulture and pest management expert with the Washington State University Extension Snohomish County, said experts often design green roofs using a series of plant trays. Individual trays can easily be removed if weeds show up or if there’s any other problem, she said.

Marine said that wasn’t done at City Hall.

“Had they done trays, it would have been easier,” he said.

Waters said he feels sorry for the contractor, but under terms of the city’s agreement, the contractor has to cover the cost.

City Hall was touted during its construction as among the most environmentally friendly public buildings in Snohomish County.

A green roof also is planned for the new Mukilteo Community Center. Construction of the new center begins next year.

The 15,000-square-foot City Hall at 11930 Cyrus Way was recognized by the Washington, D.C.-based Green Building Council in 2008 as a Leadership in Energy and Environmental Design structure.

It also includes geothermal heating and natural lighting.

Marine said he’s certain the green roof will be a boon to the city over the long term.

“If you saw it in the spring, it was very nice,” he said.

Oscar Halpert: 425-339-3429,

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