Are Small Additions Exempt from the Washington Energy Code?

The R502.1.1 Exemption — What It Actually Says

Per WAC 51-11R-50200 R502.1.1: “Additions not greater than 150 square feet in floor area shall not be required to comply with the provisions of Section R406.”

Section R406 is the energy credit section — the part of the code requiring you to earn a certain number of “credits” by choosing efficiency upgrades. For projects exempt from R406, you don’t need to pick credits, fill out the Schedule R worksheet, or calculate energy performance trade-offs.

This is the section wsec.ai’s wizard exists to help with. If your addition qualifies for the R502.1.1 exemption, you don’t need our tool.

What Still Applies (Even for Exempt Additions)

The R502.1.1 exemption is narrow — it only waives R406. The rest of WSEC-R still applies to your addition:

• R402 — Envelope requirements: New walls, floors, and ceilings in your addition must meet minimum R-values for your climate zone.
• R403 — Mechanical systems: Any new mechanical equipment installed must meet current efficiency requirements. Duct insulation requirements still apply.
• R404 — Lighting: New lighting installed in the addition must meet high-efficacy requirements.

Don’t read “R406 exempt” as “WSEC exempt.” You still need code-minimum construction; you just don’t need the credit-selection math.

Exactly 150 Square Feet — The Code Contradicts Itself

An addition of exactly 150 square feet is, by the letter of the code, both exempt from Section R406 and required to earn 2.0 credits under it. Two provisions cover the same square footage and disagree:

• R502.1.1 exempts additions “not greater than 150 square feet” — and “not greater than 150” includes 150.
• Table R406.3, item 5 charges 2.0 credits for additions “150 square feet to 500 square feet” — and “150 to 500” also includes 150.

Both readings are literal. wsec.ai treats exactly 150 square feet as exempt, because R502 is the scoping section — it decides which additions enter R406 at all, and Table R406.3 only prices the ones R502 sends there. An addition sitting exactly on the exemption line is de minimis; charging the full credit package at the threshold the code chose as its floor would read the exemption out of the code.

Projects at exactly 150 sq ft get a caveat in the app showing both citations. If your building official reads it the other way, their reading governs — and you’ll have the citation ready before you submit.

Examples

• 8’ × 12’ bedroom addition (96 sq ft) — R406 exempt. R402/R403/R404 apply.
• 10’ × 14’ sunroom (140 sq ft) — R406 exempt.
• 10’ × 15’ addition (exactly 150 sq ft) — the overlap above. wsec.ai treats it as R406 exempt and flags the conflicting citation.
• 12’ × 14’ kitchen bump-out (168 sq ft) — exceeds 150 sq ft, NOT exempt. Falls in the 150–500 tier (2.0 credits required).
• 20’ × 25’ family room addition (500 sq ft) — addition-small tier boundary (2.0 credits required at exactly 500 sq ft).

What Documentation You Still Need for Permitting

Even with the exemption, your local AHJ will likely require:

• Construction drawings showing the addition
• Insulation specifications meeting R402 minimums
• Mechanical equipment specifications (if installing new equipment)
• A statement that the addition qualifies for R502.1.1 exemption — this is usually a simple line on the building permit application or a one-page certification

When the Exemption Doesn’t Apply

The R502.1.1 exemption is ONLY for additions. It does NOT apply to:

• Alterations or renovations of existing space (those have their own Chapter 5 rules)
• New construction of any size
• Repeat applications — you can’t claim two 100 sq ft additions to skirt the threshold; AHJs treat connected work as one project

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