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  • Writer's pictureMarkus Virta

Navigating Major Changes in the 2021 WSEC

The 2021 Washington State Energy Code (WSEC) will become effective on July 1, 2023, replacing the 2018 WSEC. This update is crucial in achieving the state's 2030 mandate of zero fossil fuel emissions in new construction and a 70% reduction in energy use compared to the 2006 code. The State Energy Code Technical Advisory Group (TAG), State Building Code Council (SBCC), and the Mechanical, Ventilation and Energy (MVE) Code Committee have worked extensively to develop the new code.


The 2021 WSEC features well over 100 updates to the state energy code. For the purpose of this blog we are going to focus on the changes relating to solar PV systems and WAC 51-11C-41100 Section C411.

On-site Renewable Energy:

  1. New Commercial Buildings and additions larger than 10,000 square feet must include a renewable energy generation system (i.e. solar).

  2. Minimum capacity is 0.5 W/ft2 or 1.7 Btu/ft2 multiplied by the gross conditioned floor area.

  3. Exceptions apply if:

    1. Over 50% of the roof area is shaded for more than 2500 annual hours between 8:00 a.m. and 4:00 p.m.

    2. Over 80% of the roof area is covered by equipment other than on-site renewable energy systems, planters, vegetated space, skylights, or occupied roof decks.

    3. Buildings lacking adequate roof area for required on-site solar installation may install a lesser amount of on-site renewables, but not zero.

Additional Efficiency Credits:

  1. Buildings qualifying for one of the exceptions must achieve an additional 18 efficiency package credits from Table C406.2 (below).

  2. The additional 18 credits can be reduced based on a prorated fraction of renewable capacity installed on-site.

Table C406.2 is cut off by a page break in the code. It continues below:

On-site and Off-site Renewable Energy Accounting:

  1. Qualifying renewable energy must meet specific requirements.

  2. Renewable energy certificate (REC) tracking. For multitenant buildings where RECs are transferred to tenants, the plan for operation shall include procedures for tracking the quantity and vintage of RECs that are required to be retained and retired. The plan shall include provisions to transfer the RECs to building tenants, or to retire RECs on their behalf, in proportion to the gross conditioned and semi-heated floor area leased or rented. The plan shall include provisions to use a REC tracking system that meets the requirements of Section V.B of the Green-e Framework for Renewable Energy Certification. The plan shall describe how the building owner will procure alternative qualifying renewable energy in the case that the renewable energy producer ceases. C411.2.3

  3. The following are considered qualifying off-site renewable energy systems:

    1. Self-generation systems complying with Section C411.2.2.

    2. Community renewable energy facility systems complying with Section C411.2.2.

  4. Purchase contracts complying with Section C411.2.3.

Off-site Renewable Energy Documentation

  1. Documentation of off-site renewable energy procurement must be submitted to the code official.

  2. Purchase contracts must have a duration of at least 15 years.

  3. Records on renewable power purchased by the building owner from the off-site generator must be retained or retired by the building owner and made available for inspection by the code official upon request.

Solar Readiness

  1. A solar zone must be provided on buildings 20 stories or less in height above grade, either on the roof or another structure on the site.

  2. Exceptions apply under the following conditions:

    1. Solar exposure of the building's roof area is less than 75% of that of an unshaded area.

    2. Buildings, building additions, or changes in space conditioning or occupancy with a total floor area equal to or less than 500 square feet.

  3. Solar zone requirements include:

    1. Minimum area determined by 40% of roof area or 20% of electrical service size.

    2. Solar zones can consist of separated subzones, each at least 5 feet wide.

    3. Solar zones must be free of obstructions, except those serving photovoltaic systems within the zone.

    4. Proper shading and structural integrity must be maintained.

    5. Access pathways and provisions for emergency smoke ventilation must be provided as required by the International Fire Code.

    6. Future photovoltaic system interconnection provisions must be included in the design.

      1. A space for the mounting of a future overcurrent device, sized to accommodate the largest standard rated overcurrent device that is less than 20 percent of the bus rating.

      2. Lugs sized to accommodate conductors with an ampacity of at least 20 percent of the bus rating, to enable the mounting of an external overcurrent device for interconnection.

      3. The electrical construction documents shall indicate all of the following:

        1. Solar zone boundaries and access pathways.

        2. Location for future inverters and metering equipment.

        3. Route for future wiring between the photovoltaic panels and the inverter, and between the inverter and the main service panel.

The 2021 Washington State Energy Code (WSEC) represents a significant opportunity for the Washington State solar industry. The code's emphasis on on-site renewable energy systems, including solar PV, provides an opportunity for solar businesses to play an important role in new commercial developments. As commercial construction developers seek to comply with the new code, experience and in depth knowledge of PV system design, contractor engagement, selection, and construction oversight of rooftop PV systems will be critical in ensuring that they maximize the benefits of renewable energy while meeting the latest energy code requirements.


Whether a project calls for onsite, a combination of onsite and offsite solar, or solar ready zones, commercial developers have an opportunity, by leveraging our team's expertise, to position themselves as leaders in sustainable construction. Cascadia Renewables is committed to providing top-notch service and support to ensure that our clients meet their renewable energy goals and comply with the latest energy code requirements.


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- Markus and Callum



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