Window Replacement in Washington State: L&I Rules and Climate

This article is about Washington State, not Washington, D.C. In Washington State, window replacement is construction work, and the Department of Labor & Industries (L&I) states that "Washington State requires all construction contractors to register with L&I" (L&I: register as a contractor; L&I contractor verification) ¹³. You can check any installer's registration in L&I's online lookup before you sign.

The other half of the answer is weather. The Cascade Mountains split the state into two climates: a wet, mild, cloudy west and a drier, sunnier east with hotter summers and colder winters ⁵⁶. All 39 Washington counties fall in ENERGY STAR's Northern climate zone, so the same window criteria apply statewide, but what matters most on a given house may differ: condensation and rain in Seattle or Olympia, summer sun and deep cold in Spokane or Yakima ⁸⁹.

L&I contractor registration

L&I's registration page says all construction contractors must register, and it describes two types: general contractors, who "can perform most types of construction work," and specialty contractors, who "can only perform work in the specialty they are registered in" (L&I: register as a contractor) ¹. L&I's advice to homeowners notes that hiring a registered contractor does not guarantee that problems won't happen, but that it may give you protections that are not available otherwise (L&I: hiring a contractor) ².

Exemptions in state law

The exemptions sit in RCW 18.27.090. Two matter most for a homeowner (RCW 18.27.090) ⁴:

• Small, casual work. Work on one project where the aggregate contract price for labor, materials and all other items is less than $500 is exempt as "casual, minor, or inconsequential." The exemption does not apply when the work is part of a larger job, when a job is split into contracts under $500 to evade the law, or to a person who advertises in a way that suggests they are a contractor ⁴.
• Your own property. A person working on their own property is exempt, but not someone doing contractor work on their own property in order to sell, demolish or lease it ⁴.

A window job priced at $500 or more falls outside the small-work exemption, so for most hired installations the registration rule is the one to plan around (RCW 18.27.090) ⁴.

How to check a Washington contractor

L&I's verify tool searches by name, contractor or tradesperson license number, workers' comp account or Washington UBI number ³. L&I's hiring guidance includes these suggestions ²:

• confirm the contractor has an active license;
• review the license history for previous lawsuits or license violations;
• get references and a written contract whose terms you understand.

Is the installer registered as a general contractor, or as a specialty contractor whose specialty covers window work? Ask, then confirm it in the L&I lookup ¹³. The guide on how to choose a window installer covers the rest of the vetting.

Washington's climate, east and west of the Cascades

The 2025 State Climate Summary for Washington, from the North Carolina Institute for Climate Studies at North Carolina State University, explains that the Cascade Mountains act as a physical barrier, so the climate differs greatly between the western and eastern parts of the state ⁵. The Washington State Climate Office puts it simply: western Washington "is much wetter and milder than eastern Washington," and eastern Washington is generally colder in winter and warmer in summer ⁷.

The wet, mild west

West of the Cascades, the Western Regional Climate Center describes summers as cool and comparatively dry and winters as mild, wet and cloudy ⁶. Most of the state's precipitation falls in winter ⁵. The strongest winds there generally come from the south or southwest in late fall and winter, and in the interior valleys winds can be expected to reach 40 to 50 mph each winter ⁶.

For windows, that means long stretches of cool, damp weather with the heating on. NFRC's consumer guide at efficientwindows.org explains that condensation forms when the inside surface of a window is colder than the indoor air, and that it can lead to mold and mildew ¹². Wind-driven rain also tests the seal between the window and the wall. The Department of Energy notes that even the most energy-efficient windows can leave a house drafty and lead to moisture condensation if they are not properly installed ¹⁵.

The drier, sunnier east

East of the Cascades, summers are warmer, winters are colder and precipitation is lower than in the west ⁶. In summer, the east gets 80 to 85 percent of possible sunshine ⁶. Winters bring the opposite problem: average minimums below 30 °F across central and eastern Washington ⁵. A window here has to hold heat in through a cold winter and manage strong sun through a hot summer.

Wildfire smoke and closed windows

Washington's Department of Health advises residents during smoke events to "close windows and doors, unless it is too hot to maintain safe temperatures," and to reopen them when air quality improves, such as during rain or wind shifts ¹⁶. If you are replacing windows, a sensible check is that every new sash closes and locks fully, and that you know which windows you will open for cross-ventilation once the air clears ¹⁶.

What the climate means for frames and glass

ENERGY STAR sets window criteria by climate zone, using ratings from the National Fenestration Rating Council (NFRC) ¹⁰. Every Washington county is in the Northern zone in ENERGY STAR's county list, from King and Pierce to Spokane, Yakima and Walla Walla ⁹. The Northern criteria are ⁸:

All ENERGY STAR windows, in every zone, also have to meet an air leakage limit of 0.3 cubic feet per minute per square foot ⁸.

Reading the NFRC label

• U-factor measures how well the window keeps heat from escaping; lower is better, and the label scale runs from 0.20 to 1.20 ¹¹. In a long, cool western Washington heating season and a cold eastern winter alike, this is the number that ENERGY STAR caps for the Northern zone ⁸.
• SHGC (solar heat gain coefficient) measures how much solar heat comes through, from 0 to 1; low numbers resist solar heat and high numbers allow it ¹¹. The Northern zone sets a minimum rather than a maximum, because winter sun can help heat a house ⁸. DOE's orientation table for cold climates suggests the lowest U-factor you can afford on north-facing windows, the highest SHGC with the lowest U-factor you can afford on south-facing ones, and a low SHGC or shading on east and west windows ¹⁵. In the sunny east, the question of shading west-facing glass may come up more often.
• Air leakage measures how much air enters through the window; ENERGY STAR caps it at 0.3 cfm per square foot ⁸¹¹.
• Condensation resistance is rated on a scale of 1 to 100, and the higher the number, the less likely condensation is to form on the inside surface ¹². The same guide advises a significantly higher rating in colder climates ¹². It is worth asking for on any quote in the damp west.

Frames and spacers

The consumer guide says the frame and sash make up 10 to 30 percent of a window's area, that the frame material has a major impact on the window's thermal characteristics, and that the U-factor takes in both frame and glass ¹³. Common frame materials include wood, clad wood, vinyl, fiberglass, composites and aluminum, with or without a thermal break ¹³. Rather than comparing materials in general, compare the rated U-factor and condensation resistance of the exact unit quoted; the frame materials comparison covers durability and upkeep.

The spacer between the panes matters for condensation too. The guide notes that in cold climates spacer systems can reduce heat loss, condensation and water damage, that non-metallic and warm-edge spacers cut condensation, and that heat and cold pass easily through metal spacers ¹⁴.

Questions for a Washington quote

• What are the NFRC-rated U-factor, SHGC, air leakage and condensation resistance of the exact window quoted, and does it meet ENERGY STAR's Northern criteria ⁸¹¹?
• What spacer system does the glass use ¹⁴?
• How will the installer flash and seal the opening against wind-driven rain?
• On a sunny east-side or west-facing wall, is the glass the same on every side of the house, or matched to orientation ¹⁵?

The energy-efficient windows explainer and the article on window condensation go deeper on both topics.

Cost and next steps

Washington prices follow the same drivers as anywhere: the number of windows, frame material, glass package, full-frame or insert installation, and labor. This page does not quote Washington or city prices, because the national surveys do not publish reliable local figures; the window replacement cost guide sets the national surveys side by side. Whether your job needs a permit depends on your city or county, and the article on window replacement permits explains why answers differ.

When you are ready, you can compare quotes from window installers.

About these figures

• ¹ Official record: L&I statement that all construction contractors must register, and the general and specialty contractor types, checked October 26, 2026.
• ² Official record: L&I hiring guidance (active license, license history, references, written contract, registration not a guarantee), checked October 26, 2026.
• ³ Official record: L&I verify tool search fields, checked October 26, 2026.
• ⁴ Official record: RCW 18.27.090(9) and (12), the under-$500 casual-work exemption and its limits, and the own-property exemption, checked October 26, 2026.
• ⁵ Reported: North Carolina Institute for Climate Studies 2025 State Climate Summary for Washington (precipitation over 100 inches west, under 10 inches in Central Washington, summer highs, winter lows, winter precipitation), checked October 26, 2026.
• ⁶ Official record: Western Regional Climate Center Washington narrative (west and east seasons, sunshine percentages, winter wind speeds), checked October 26, 2026.
• ⁷ Official record: Washington State Climate Office description of the wetter, milder west and the colder-winter, warmer-summer east, checked October 26, 2026.
• ⁸ Official record: ENERGY STAR Northern zone criteria and the 0.3 air leakage limit, checked October 26, 2026.
• ⁹ Official record: ENERGY STAR county climate zone spreadsheet listing all 39 Washington counties in the Northern zone, checked October 26, 2026.
• ¹⁰ Official record: ENERGY STAR statement that criteria vary by climate zone and rest on NFRC ratings, checked October 26, 2026.
• ¹¹ Official record: NFRC label definitions and scales for U-factor (0.20 to 1.20), SHGC (0 to 1) and air leakage, checked October 26, 2026.
• ¹² Official record: NFRC consumer guide (efficientwindows.org) explanation of condensation and the 1-to-100 condensation resistance rating, checked October 26, 2026.
• ¹³ Official record: NFRC consumer guide (efficientwindows.org) statement that sash and frame are 10 to 30 percent of window area and list of frame materials, checked October 26, 2026.
• ¹⁴ Official record: NFRC consumer guide (efficientwindows.org) description of spacer systems and condensation, checked October 26, 2026.
• ¹⁵ Official record: DOE Energy Saver consumer guide on installation and cold-climate orientation guidance, checked October 26, 2026.
• ¹⁶ Official record: Washington State Department of Health smoke guidance on closing and reopening windows, checked October 26, 2026.