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A new computer modeling tool developed in Portland is geared to help engineers and architects design green roofs to manage stormwater.

Portland-based green roof manufacturer Columbia Green Technologies recently launched a green roof stormwater performance model, developed in partnership with Portland State University researchers. The company has started using the tool while working with architects and engineers to predict how much rain hitting a planned green roof in a specific geographic location will be retained in the soil and how much will eventually drain out.

Data produced by the model, using factors like predicted weather patterns and scale and thickness of a proposed green roof, will aid architects and engineers in designing green roofs that are optimized for stormwater management, said Elaine Kearney, technical director at Columbia Green Technologies and a licensed landscape architect.

鈥淲e can get a little more sophisticated in terms of the performance of our green roofs,鈥� she said. 鈥淲here we are right now is getting (the tool) into designers’ hands.鈥�

Information gleaned from the modeling tool can prove that green roofs 鈥� like bio-swales and other more traditional methods of capturing and filtering runoff 鈥� are a viable alternative to meet city or county requirements for proposed developments to manage stormwater, Kearney said.

鈥淓very designer is faced with many possibilities,鈥� she said. 鈥淎 lot of times they are faced with a situation where they are deciding how to treat stormwater on-site 鈥� A lot of what they’re looking for is some solid numbers to make those decisions. When it comes down to it, stormwater is one of the biggest factors in making a green roof pencil out.鈥�

Development of the modeling tool was supported through an $80,000 grant awarded in 2012 to Columbia Green Technologies through Oregon BEST‘s commercialization program. The state-funded nonprofit, which supports clean technology innovation, paired the company with now-retired PSU professor Graig Spolek. His research in the university’s Green Building Research Laboratory using a rain simulator above trays containing a typical green roof soil mixture produced hard data on how much water was retained or flowed out over a certain period of time. This information was used to create Columbia Green Technologies’ modeling tool.

The Oregon BEST facilitated partnership is paying off, said Ken Vaughn, director of the organization’s commercialization programs.

鈥淓verybody is really interested in the aesthetics of green roofs,鈥� he said. 鈥淏ut increasingly people think about them in practical terms and how they retain and detain stormwater 鈥� Up until this work, there was no way to model with that type of precision on how a green roof can perform in terms of stormwater treatment.鈥�

Kearney traveled this week to Houston to give a presentation discussing the modeling tool at the American Society of Civil Engineers’ International Low Impact Development Conference and said the company’s research with PSU has broad ramifications for the industry. Civil engineers and architects are hungry for stormwater performance data to inform planning for green roofs and potentially combine them with other means of managing runoff, she said.

鈥淎 lot of the data that’s out there is on the retention of stormwater, and that’s the amount that stays in the green roof, (but) not a lot in detention, which is how long it stays in the green roof before it flows out,鈥� she said.

The advantage of using the modeling tool is it produces graphs that compare the amount of rainwater that flows off a green roof during a larger storm compared to a conventional roof surface, Kearney said.

鈥淵ou get this immediate graphic description,鈥� she said. 鈥淭hat’s really valuable because the engineer can say I can count on this exact performance. It’s always been an unknown just being able to put data behind it to get a full picture. It’s basically information to help people make an informed decision.鈥�