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United States

U.S. Climate Zone 3C home maintenance

San Diego is representative for analysis; determine the actual county zone through the official PNNL file.

Official profile

3CWarm–MarineRepresentative: San Diego, California

Zone 3C is DOE’s Warm–Marine classification represented by San Diego, California; ENERGY STAR shows R49 for an uninsulated attic and R38 where 3–4 inches exist.

Official insulation comparison

Official insulation comparison for U.S. Climate Zone 3C home maintenance
ConditionGuidanceScope
Uninsulated atticR49ENERGY STAR retrofit recommendation for Zone 3.
Existing 3–4 inchesR38Official 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

    Inspect exterior joints and wood finish condition.

    A measured condition survey should precede recoating.

  2. Summer

    Map attic air leaks and uneven insulation.

    Air sealing comes before top-up.

  3. Fall

    Check roof drainage and interior staining.

    Moisture sources must be repaired rather than concealed.

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.