The Business Case: Seattle Green Roof Saves $70,000 on Stormwater

This article is reprinted with permission from Living Architecture Monitor – June, 2016

The ‘Little Wing’ office building was constructed on a corner lot in Seattle next to existing, adjacent residential buildings in 2013. The building’s core was placed to one side in order to maximize the efficiency of plumbing utilities and to provide a buffer between the adjacent residential uses. The civil engineer had initially planned to do underground detention tanks to meet on-site stormwater regulatory requirements, but Jason Twill, Vulcan Inc. Project Manager, challenged the team to see if a combination of a green roof for retention/filtration and rainwater harvesting tanks for non-potable water reuse could do double-duty… which they did.

By eliminating underground stormwater detention (~$80k), and a secondary storm/sewer discharge connection 18 feet below the street, which would have required excavation, street closures, etc. to the cost of approximately $170k, the project was able to save roughly $250,000 on traditional infrastructure. This savings more than paid for the cistern, (~$140k) and allowed the size of the green roof to be roughly doubled to 4,200 sf. The extensive green roof was a layered system provided by Columbia Green Technologies, which also provided technical support to the design team. In addition to providing an immediate “green” amenity to the building, the project also received more LEED points as a result of the inclusion of the vegetated roof. The net savings from stormwater alone was $70,000.

Project Overview

• Project: ‘Little Wing’. Built 2013
• 54,000 sf Experience Music Project administrative office building
• Location: Seattle, Washington
• LEED platinum
• Uses a combination Cistern / Green Roof to manage stormwater
• Extensive Green Roof: 4,200 sf
• Green Roof System: Columbia Green Technologies’ Extensive Layered
• System planted with sedum tiles
• Cost: Rainwater harvesting cistern (~$140k)
• Cost: Green Roof (~$40k)
• Savings: Eliminate underground detention tank (~$80k)
• Savings: Eliminate secondary storm/sewer discharge connection below the street (~$170k)

Project Team

Vulcan Inc.                        Owner / Developer
Howard S. Wright            General Contractor
Collins Woerman             Architect
Wayne’s Roofing, Inc      Green Roof Installer
Columbia Green                Green Roof Provider

Courtesy: Columbia Green Technologies. 

Written by Andrea Saven, GRP, LEED AP, RLA

Technical Director, Columbia Green

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