Seattle Energy Code (SEC) for Residential Buildings

Where do I find the Seattle Energy Code?

If your project is inside Seattle city limits, you do not file under the state 2021 WSEC-R alone. Seattle adopts its own version, the Seattle Energy Code (SEC), which is the state code plus local amendments. For most residential projects the SEC is materially similar to the state code, but there are differences worth knowing before you start your plan set.

When the SEC applies

The Seattle Energy Code applies to permit applications submitted to the Seattle Department of Construction and Inspections (SDCI). The current edition is the 2021 SEC, effective for permits applied for on or after March 15, 2024.

For dwelling-type definitions — which buildings use the residential provisions versus the commercial provisions — the SEC follows the same split as the state code. Use the residential provisions for:

• One-family dwellings
• Two-family dwellings (duplexes)
• Townhouses
• R-3 buildings of three stories or less above grade
• R-2 buildings of three stories or less where dwelling units are accessed directly from the exterior

Use the commercial provisions for everything else, including 4-story-and-taller multifamily buildings and any multifamily building where dwelling units are accessed from interior corridors.

How the SEC differs from the state code (residential)

The 2021 SEC tracks the 2021 state WSEC-R closely. SDCI's official summary states that "stringency levels of existing 2018 SEC provisions are maintained, and a few 2021 amendments provide greater efficiency than both the 2018 SEC and the 2021 state code."

In practical terms for residential projects, expect:

• Stricter local enforcement. Seattle plan reviewers tend to ask for more documentation than smaller jurisdictions — a fully completed energy compliance certificate, supporting calculations for any UA trade-off, and explicit R406 credit selections shown on the plans.
• Local amendments to specific sections. A handful of SEC sections add stricter requirements than the state code or remove certain alternatives. The current text is published by SDCI and the International Code Council.
• Additional documentation at submittal. SDCI may request items beyond what your typical small-county AHJ wants.

For commercial projects (multifamily 4-story and up, mixed-use, ADUs in some cases), the SEC has more substantive differences from the state code, particularly around heat pump requirements and dedicated outside-air system efficiencies. Those projects need a designer or energy consultant who works in Seattle regularly.

Where to find the current SEC text

The authoritative source is the City of Seattle:

• SDCI Energy Code overview: seattle.gov/sdci → Energy Code
• 2021 SEC (read-only): linked from the SDCI page above

You can also view the 2021 SEC residential chapter on the UpCodes Seattle viewer for free.

Using WSEC.ai for a Seattle project

WSEC.ai's wizard runs the state 2021 WSEC-R calculation. For a Seattle project, the state code is your baseline, and the SEC adds amendments on top. We recommend:

1. Run the full WSEC.ai compliance check to lock in your prescriptive or UA trade-off path and your R406 credit selections.
2. Cross-check the SDCI Energy Code page for any current local amendments that affect your specific project type.
3. For complex or commercial Seattle projects, use a Plan Review — we will flag SEC-specific items before you submit.

If SDCI rejects a WSEC.ai-generated submittal because of a Seattle-specific amendment, email us at hello@wsec.ai with the correction request and we will help you resolve it.