That’s not just dirt they’re spreading on the roof at Pacific Plaza, there between South 12th and 13th streets and between Pacific Avenue and Commerce Street in downtown Tacoma.

It’s Tagro – a product composed of recycled material best described as compost. Including biosolids. With sawdust and other growth media.

Now brown, that roof will soon be green, as will the building itself – but in another way.

Flowers will bloom and the rain that falls in the autumn will be collected in a cistern located below street level. Grass will grow and flowers will colorfully awaken, all to the delight of the workers who inhabit the higher floors of nearby office buildings.

The garden will not be open to the public, but it will serve the public good.

So green is the building that it will likely earn LEED Platinum status – LEED from Leadership in Energy and Environmental Design – as awarded by the U.S. Green Building Council. It’s a rating only the buildings that meet strict criteria for energy efficiency and environmental benefit can earn.

So green is Pacific Plaza that it likely will serve as a standard by which other buildings are measured.

So says Dan Putnam, a principal developer of the project and CEO of PCS Structural Solutions, a company that will occupy a slice of the office space on an upper floor of the building.

“It’s become a better and better project as we went along,” Putnam said this week.

The project: What once was merely a parking garage with a nod to retail – Park Plaza South – will become a parking garage, retail space and office building combined.

Cost: “North of $40 million,” Putnam said.

Design: BLRB Architects.

Owners: Pacific Plaza Development LLC owns the air rights and has secured a 99-year lease with the City of Tacoma for the ground. The city remains owner of the parking facilities, which will be managed by Republic.

Space: 35,000 square feet can accommodate retail and a restaurant facing Pacific Avenue; 70,000 square feet available for office space on the top two floors; 150,000 square feet can accommodate 500 cars.

Office space: Seventh floor pre-leased to PCS Structural Solutions and BLRB Architects; eighth floor is available. “We’re about to announce some significant leases,” Putnam said. “It didn’t hurt for DaVita to stay.”

That roof: Putnam credits Craig Sivley, former assistant public works director for the city, with coming up with the idea for a turf roof. Putnam admitted he was reluctant. “I said a soft ‘no’ three or four times. He kept asking.”

Watering the 30,000-square-foot roof: Rainwater will be collected in a cistern – with a capacity of 190,000 gallons – that once served as a bathhouse. The cistern also will supply water for toilets and urinals. Oil-soaked rainwater once went from the site into the Thea Foss Waterway. No longer.

Green roof size matters: “We’re pretty sure it’s the largest in Washington,” Putnam said.

Cost of turf roof: $200,000 for Tagro and installation.

Other green matters: Exterior “Swisspearl” facade composed of recycled material. Skylights and large windows will help with lighting. HVAC systems upgraded for sustainable practices.

Special features: Sides of the building will be lit by structural “lanterns” as the enclosed stairwells are opened and extended beyond earlier dimensions.

The real payoff: Putnam, who grew up in Tacoma, calls the project “a dream come true.” He recently invited his mother, Lois, to come up to the roof and see what her son had done. “She was overwhelmed,” he said.

C.R. Roberts: 253-597-8535

c.r.roberts@thenewstribune.com