Item No: 8g_Attach 
Date: March 22, 2022              P.O. Box 1209 
P.O. Box 1209 
Seattle, WA 98111-1209 
Seattle, WA 98111-1209 
Tel: 787-3000 
Tel: 787-3000 
www.portseattle.org 
www.portseattle.org 
SUSTAINABLE DESIGN APPROACH 
WORLD TRADE CENTER WEST (WTCW) ROOF REPLACEMENT 
PURPOSE 
This serves as a summary document for the sustainable design coordination for the World Trade
Center West (WTCW) Roof Replacement project. Additional information can be found in Project
Management's Notebook. 

SUSTAINABLE DESIGN APPROACH 
The WTCW Roof Replacement project has been identified as a Tier 2 project under the Sustainable
Evaluation Framework Policy Directive (SEF Policy Directive) adopted by the Port of Seattle
Commission in January 2020. Tier 2 projects are described as: 
Tier 2: Medium-sized, or more complex, projects that have opportunities for sustainability benefit
would be subject to targeted sustainability analyses and strategies. Tier 2 projects may receive a
cost per ton of carbon calculation. 
The scope of the project is to replace the existing 17,000 square foot roof on top of the WTCW
building.







Figure 1. WTCW Roof Replacement Project 
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Following the project kickoff meeting, the Project Manager and Sustainability Coordinator assembled
a Sustainable Project Assessment and Review Collaboration (SPARC) team The SPARC team
leverages port expertise and knowledge of existing and emerging sustainability practices to: 
(1) Identify, review, brainstorm, and recommend sustainability concepts and ideas for project and
operational teams to consider and evaluate during the development and design stage of port projects. 
(2) Encourage project and operational teams to evaluate and consider innovative strategies to reduce
emissions and energy use beyond traditional approaches. 
(3) Select and apply the relevant Sustainable Evaluation Framework criteria to highlight tradeoffs
and benefits during development of the Sustainable Design Approach (SDA).
PROJECT GOALS 
The SPARC team met in August 2021 to solidify project goals which were shared with the designer to
identify potential design alternatives/strategies moving into the 30% design process. 
Energy Efficiency and Environmental Health 
o  Reduce heat island effect within the urban core 
o  Explore opportunities to reduce the building's and construction project's carbon
footprint (ie, buy local, material reuse, recycled content, energy efficiency) 
o  Explore solar and Green Roof Technology 
o  Utilize construction best management practices 
Sustainable Asset Management 
o  Maximize total cost of ownership 
o  Consider ease and frequency of maintenance 
Materials 
o  Reuse materials if possible 
o  Consider environmentally-friendly alternative materials 
o  Reduce waste 
Financial Sustainability 
o  Balance project cost and function against environmental benefits 
Impacts to Tenant 
o  Ensure a safe project 
o  Minimize tenant and visitor disruptions 
SUSTAINABLE EVALUATION FRAMEWORK CRITERIA 
The goals identified by the SPARC team support three of the seven criteria articulated in the SEF
Policy Directive: 
Reduce GHG Emissions/Protect Health and the Environment. This project focuses on the
replacement and upgrade of existing infrastructure while limiting environmental impacts. Goals
focus on materials, reduction of carbon footprint, and construction best management practices. 
The project will explore that incorporation of solar. 

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Increase Resilience. The proposed improvements will upgrade the existing roof, limiting
future damage to the existing structure and upgrading the roof to meet current code
requirements. 
Advance Innovation. This project will explore the option of installing a green roof, which has
not been utilized by the Port before. 

SUSTAINABLE DESIGN STRATEGY 
The aforementioned goals were used to evaluate three design alternatives, two of which were analyzed
as feasible alternatives. A cost-benefit analysis was assembled for each alternative and
recommendations were presented to the project sponsors in October of 2021. 
DESIGN STRATEGIES 
Alternative 1: In-kind System. This was the original design plan for the project. This entails
installing new insultation where necessary, replacing the existing roof membrane, and installing
a roof overlay. For sustainability measures, design is reusing as many materials as are feasible
(ballast, insulation). Since this is an in-kind consideration, it was moved forward for further
consideration. 
Alternative 2: Green Roof. This design alternative considers the installation of green roof
technology. Elements include leaving the existing insulation and roof membrane in place,
installing a new membrane over existing, reusing as many materials as possible (ballast), and
installing approximately 11,000 square feet of green roof. This design allows for additional
environmental benefits and is technically feasible (ie, weight is comparable to weight of
existing ballast), so was moved forward for further consideration. 
Alternative 3: Solar. This design alternative considers the installation of solar technology.
Elements include leaving the existing insulation and roof membrane in place, installing a new
membrane over existing, reusing as many materials as possible (ballast), and installing solar
panels. This alternative was not carried forward due to glare and reflection concerns on
neighbors, poor positioning for solar energy, and constraints with the existing roof to hold the
additional weight of the solar panels. 
SUSTAINABLE DESIGN ALTERNATIVES ANALYSIS 
A cost-benefit analysis was prepared for Alternatives 1 and 2. Table 1 provides the summary matrix of
how each alternative meets the project goals. It was determined that Alternative 2, Green Roof, is
preferred since it provides multiple environmental benefits at a moderate cost increase. This is the first
green roof the Port will install and can serve as an innovative pilot project for consideration at other
sites in the future. Additional details are provided below. 
Alternative 1: In-kind System. An in-kind replacement roof is the lowest cost alternative but 
does not provide any environmental benefits and continues to contribute to typical issues facing
developed areas (heat island effect, high temperature runoff, carbon footprint, minimal habitat,
etc). 
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Alternative 2: Green Roof. Use of a Green Roof provides and innovation example and an
opportunity for the Port to pilot a new technology and achieve significant environmental
benefits in a location where none were previously. This alternative reduces heat island effect,
sequesters carbon, retains stormwater, reduces runoff temperature, creates additional pollinator
habitat, and provides additional rooftop insultation and interest to those tenants with a site line
to the roof. The initial and 20-year life cycle cost is more expensive than in-kind replacement,
but green roofs can potentially last for up to 50 years if maintained properly. 















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Table 1. Alternatives Analysis WTCW Roof Replacement 
Energy Efficiency and Environmental Health                          Materials                   Sustainable Asset Management/                        Tenant Impact 
Financial Sustainability 
Heat Island     Carbon Footprint       Stormwater         Habitat        Reuse of materials        ROM Cost     Life Cycle Cost     Maintenance      Tenant Disruption         Aesthetics 
Effect Reduction      Reduction      Retention/ Protection    Creation                                                   (20 years)*      Requirements 
Alternative 1     Ballast creates a   No additional       No additional            None         Ballast and insulation         $48/SF         $98/SF            Regular           Construction noise        Neutral 
In-Kind       heat sink                                                                                                 ($1.34M)      ($2.02)           inspection 
Replacement 
Ballast area        37.5g/SF            Water retention and      Pollinator    Ballast and insulation,         $108/SF        $163/SF           Regular           Construction noise,       Visual interest for
Alternative 2 
reduced                               mitigation of high       habitat       ballast reuse offsite (habitat   ($2.28M)      ($3.36M)         inspection        provides additional       tenants with site
Green Roof 
temperature runoff                     or stormwater)                                                                    noise insulation           line to roof 
Coloring is to provide easy translation of pros and cons. Green is a benefit to the alternative, red is a detriment for the alternative. Orange is considered neutral. 
*Green roof could have a life up to 50 years, which would bring the life cycle costs closer in line with one another. 












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