Energy Code Guides
Plain-English explanations of Washington State residential energy code requirements. Written for homeowners, owner-builders, and contractors.
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📖The energy code in plain English
Every term you'll meet at the permit counter, defined without jargon — and what the county actually wants from you.
What is the WSEC?
Who the residential energy code applies to, what it requires, and which compliance path most single-family projects take.
How many credits do I need?
Find your building's size tier and the credit total you have to reach, plus where those credits come from.
Does this apply to my project?
🔧Additions & remodels
When work on an existing house triggers the energy code, and which requirements follow the scope you're doing.
Are small additions exempt? (under 150 sq ft)
Where the 150 square foot line sits, what it exempts you from, and what still applies on the other side of it.
Multifamily residential vs. commercial
Whether your multifamily project follows WSEC-R or WSEC-C, and why access type decides it rather than height alone.
Seattle Energy Code (SEC)
What changes for residential projects inside Seattle city limits, and where the SEC goes further than the state code.
I-2066 code status
What the pending state Supreme Court ruling means for your project, and what to do while it's unresolved.
Figure out your numbers
🗺️Climate zones: CZ4 vs CZ5
Look up your zone by ZIP and see what changes between western and eastern Washington. Includes the three counties that straddle the crest.
Windows and fenestration
U-factor requirements, area-weighted averaging, and why the NFRC label on the glass is the number that counts.
The UA trade-off path
How to offset a weak spot in the envelope with a strong one, and when judging the envelope as a whole beats meeting each minimum.
ERI / performance path (R405)
When whole-house energy modeling saves more than it costs — modeler fees, DIY software, and the project types where it pays off.
Choose your systems
🔥Choosing your heating system
Your single biggest credit decision. What heat pump, gas furnace, and electric resistance each earn you before anything else is chosen.
Water heating credits
Heat pump water heaters, NEEA tiers, and one of the most cost-effective places to pick up the credits you're short.
Radon-resistant new construction
Which Washington counties require passive radon mitigation, what to install at framing stage, and why retrofitting is far harder.
Build it and pass the test
💨Air sealing & blower door testing
What the test measures, when it's required, and why sealing is a framing-stage job rather than a finish-stage one.
AeroBarrier — fluid-applied air sealing
Costs, Washington installers, and how a sprayed aerosol seal fits the air-leakage credit thresholds for new construction.
Sill plate sealing and vapor retarders
Two of the most commonly failed inspection details in Washington — what's required and how to get them right the first time.
Stuck? Fix it
📋WSEC-R permit correction notices
The rejections plan reviewers write most often — short credit totals, missing glazing schedules, UA shortfalls — and the fix for each.
Failed blower door rescue
Test came in over target? Your options, from targeted sealing to credit swaps, without tearing out drywall.
WSU C3 calculator: common problems
Macro errors, antivirus blocks, crashes, and plan review rejections — how to work through each one.
How to run the calculator on a Mac
The C3 workbook is Windows-only. What actually works on a Mac or iPad, and what to skip.
WSU C3 alternatives
The options besides the state spreadsheet, side by side, and which one suits the project you're documenting.
Does REScheck work in Washington?
Short answer: no. Why the national tool doesn't satisfy a WSEC-R permit, and what to submit instead.