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United States

U.S. Climate Zone 4C home maintenance

Seattle is a representative analysis location; confirm the project zone through PNNL county data.

Official profile

4CMixed–MarineRepresentative: Seattle, Washington

Zone 4C is DOE’s Mixed–Marine classification represented by Seattle, Washington; ENERGY STAR shows R60 for an uninsulated attic and R49 with 3–4 inches existing.

Official insulation comparison

Official insulation comparison for U.S. Climate Zone 4C home maintenance
ConditionGuidanceScope
Uninsulated atticR60ENERGY STAR groups Zone 4C with Zones 5 and 6 for this retrofit table.
Existing 3–4 inchesR49Official retrofit table condition

This is a comparison value, not a bag count. Choose the applicable added R-value and a current named-product label before calculating material.

Calculate named-product bags

Seasonal priorities for this profile

  1. Spring

    Trace roof and wall water paths.

    Wet assemblies must be corrected before insulation or finish work.

  2. Summer

    Inspect attic air sealing and ventilation details.

    Intentional ventilation and leakage controls are different.

  3. Fall

    Review exterior wood and drainage condition.

    Preparation follows observed moisture and coating condition.

Use the profile correctly

  • Confirm the actual project zone using the cited official lookup or the authority that applies locally.
  • Inspect existing material, moisture, air leakage, safe access, wiring, fixtures, and combustion equipment before top-up.
  • Use the exact current product coverage card; do not transfer bag data between U.S. and Canadian products.
  • Treat representative locations as classification examples, not local forecasts or code boundaries.

Sources and scope

Source links reviewed July 16, 2026. A review date is not the document's publication date.

  1. U.S. Department of Energy: Prototype Building Models — Climate Zone RepresentativesUnited States · government standard

    Representative locations classify a zone; they are not a substitute for local weather or code data.

  2. Pacific Northwest National Laboratory: Guide to Determining Climate Zones by CountyUnited States · government standard

    Use the county files for a project address; representative cities are examples rather than boundaries.

  3. ENERGY STAR: Recommended Home Insulation R-ValuesUnited States · government guide

    Recommendations are presented by ENERGY STAR using 2021 IECC climate zones.

  4. ENERGY STAR: DIY Checks and InspectionsUnited States · government guide

    Do not disturb suspected vermiculite insulation; obtain qualified guidance before work.