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Rooftop meadow planned in West End

Daily Journal of Commerce

January 28th 2002

The first development in Portland using an eco-roof to take advantage of a height bonus offered to developers who top a building with soil and plants began construction Jan. 18.

The Mosaic, an eight-story condominium in the city's West End near Portland State University, will be completed in about 13 months.

"The entire roof will look like a meadow," said architect Jeff Myhre of the Myhre Group Architects. "Once there are larger buildings around looking down on it, we want the rooftop to be attractive."

Myhre is a principal of the Myhre Group Architects, which worked with Victoria, British Columbia architect Jan Zak to design the condominium project for Victoria developer Mosaic Properties Inc.

The city began looking into incentives to promote eco-roofs over a year ago - after Tom Liptan, an environmental consultant with the Bureau of Environmental Services, determined that living roofs could significantly ease the burden on the city's overloaded stormwater systems.

A living roof retains 15 to 100 percent of the water that falls on it, according to Liptan's calculations on test roofs. Those calculations, together with projections that rooftops will eventually cover 20 of the city's 135 square miles, convinced city officials to find ways to promote living roofs, which are more expensive for developers than a standard roof system.

An amendment allowing buildings to exceed height restrictions in exchange for topping them with eco-roofs was unanimously passed by the city council and took effect in the spring of 2001 - after The Mosaic building had already completed the first stage of design review.

"Originally we had planned a rooftop garden to be used by all tenants," Myhre explained, "but it counted as a habitable area - putting us over the FAR limitations."

FAR - floor area ratio - regulations limit a building's total floor area based on the size of its footprint or base area. Essentially, the larger a building's footprint, the more total floor area the building can contain and so the taller it can be built.

The Mosaic building sits on an unusually small lot - just 4,875 square feet - and so was severely constrained by FAR restrictions.

"When you get a site so small it becomes very challenging to design an effective layout," said Myhre. "Going vertical was the only choice to make it pencil out."

The original idea for a rooftop garden, which would have had potted plants, had to be scrapped after it was learned the space counted as habitable in the FAR calculations. To get the desired floor area for condominium space, the planners then moved ahead with a plan to donate money to a city art fund - another method to obtain FAR bonuses. The design review board approved plans based on the proposed art fund donation.

When FAR bonuses for eco-roofs became available, the building planners saw a way to move back toward original plans for plants on the roof - and obtain the necessary FAR bonuses.

So far, The Mosaic is the only building to announce plans to use an eco-roof for height bonuses, according to Ruth Selid, a city planner who helped facilitate plan approval for The Mosaic.

"The design team heard there would be an adoption of eco-roof bonuses and thought that's great - that's what they would like to be doing anyway," Selid explained.

The Mosaic will be Portland's first building built in the Vancouver, B.C. style of architecture, according to Myhre. The style is distinguished, in part, by a slender form, a concrete structural system and floor-to-ceiling, wall-to-wall glass exterior walls.

Myhre isn't sure why the style of slender glass towers associated with Canada's closest city had not made it to Portland before this. But, after putting one of the buildings through the approval process here, he thinks it may have something to do with Oregon's strict energy codes.

"Getting the building to meet energy code approval was very difficult and something we spent a lot of time on," Myhre recalled. "Most buildings that are all glass experience significant solar gains and heat loss."

To bring the design up to energy code standards, the design team specified glass with a high thermal value, and insulated concrete floor slabs where exposed at the edge of the building.

"The eco-roof helped with energy calculations, believe it or not," Myhre added. "When you have that much dirt on the roof it gives you a pretty high insulating value."