Energy Code Guides
Plain-English explanations of Washington State residential energy code requirements. Written for homeowners, owner-builders, and contractors.
What is the Washington State Energy Code?
Plain-English explanation of WSEC-R 2021 — who it applies to, what it requires, and how to comply.
Read guide →How Many Energy Credits Do I Need?
Credit requirements by building size: small (5.0), medium (8.0), large (9.0). R406.2 vs R406.3 explained.
Read guide →Climate Zones: CZ4 vs CZ5
Interactive ZIP code lookup. Western WA (CZ4) vs Eastern WA (CZ5) — what changes and why it matters.
Read guide →The UA Trade-Off Path
An alternative to prescriptive compliance. When it makes sense and how it works.
Read guide →Windows and Fenestration
U-factor requirements, area-weighted averaging, NFRC labels, and how your window package affects compliance.
Read guide →Choosing Your Heating System
The biggest single credit decision. Heat pump vs gas furnace vs electric — what each earns you under R406.2.
Read guide →Water Heating Credits
Heat pump water heaters, solar water heating, and one of the most cost-effective ways to earn R406.3 credits.
Read guide →Air Sealing & Blower Door Testing
Air leakage requirements, when testing is required, and what to expect from a blower door test.
Read guide →Radon-Resistant New Construction
Passive radon mitigation is required in seven Washington counties. What to install at framing stage and why retrofitting is much harder.
Read guide →Additions & Remodels
How the energy code applies to additions, renovations, and window replacements. Size thresholds and exemptions.
Read guide →Are Small Additions Exempt? (Under 150 sq ft)
Additions not greater than 150 square feet are exempt from R406 credit requirements under WAC 51-11R-50200 R502.1.1. Here's what still applies.
Read guide →Multifamily Residential vs. Commercial Energy Code
Under the 2021 WSEC, whether your multifamily project uses WSEC-R or WSEC-C depends on access type, not just height. Here's where the line is.
Read guide →I-2066 Code Status
What the pending WA Supreme Court ruling means for your project and what to do in the meantime.
Read guide →WSU C3 Calculator: Common Problems
Mac compatibility, antivirus blocks, macro errors, crashes, and plan review rejections — and exactly how to work through each one.
Read guide →Seattle Energy Code (SEC)
How the 2021 Seattle Energy Code differs from the state WSEC-R for residential projects inside Seattle city limits.
Read guide →Failed Blower Door Rescue
Test came in over target? Here are your options — from targeted sealing to credit swaps to AeroBarrier — without tearing out drywall.
Read guide →AeroBarrier — Fluid-Applied Air Sealing
Costs, Washington installers, and how AeroBarrier fits R406.3 Category 2 credit thresholds for new construction.
Read guide →ERI / Performance Path (R405)
When whole-house energy modeling saves more than it costs — hiring fees, DIY software, and the project types where R405 pays off.
Read guide →Sill Plate Sealing and Vapor Retarders
Two of the most commonly failed inspection details in Washington — what the code requires and how to get them right the first time.
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