Climate Zone 3 — Warm
Zone 3 represents a transitional climate that spans much of the southern United States from coast to coast. Cities like Atlanta, Memphis, Las Vegas, and much of the Carolinas fall within this zone. Both heating and cooling are significant concerns, though cooling typically dominates the annual energy budget. Buildings in Zone 3 need insulation that performs well in both summer and winter conditions. Wall insulation becomes more important in this zone compared to Zones 1-2, and floor insulation over unconditioned spaces begins to have a meaningful impact on energy consumption.
Zone 3 Climate Data
R-Value Requirements for Zone 3
The table below lists the DOE recommended insulation R-values for every building component in Climate Zone 3 (Warm). Click on any component to see detailed insulation type comparisons, thickness requirements, and cost estimates specific to that component in this climate zone.
| Building Component | Required R-Value | Details |
|---|---|---|
| Attic | R-38 | View insulation options → |
| Wall Cavity | R-13 | View insulation options → |
| Wall Continuous | None required | View insulation options → |
| Floor | R-19 | View insulation options → |
| Basement Wall | R-5 | View insulation options → |
| Crawlspace | R-5 | View insulation options → |
| Cathedral Ceiling | R-30 | View insulation options → |
| Garage Ceiling | R-19 | View insulation options → |
Insulation Thickness by Type for Zone 3 Attic (R-38)
The attic is typically the most cost-effective location for insulation in any climate zone. The table below shows the thickness of each insulation type needed to achieve the R-38 recommendation for Zone 3 attics, along with the estimated material cost per square foot.
| Insulation Type | R/Inch | Thickness Needed | Cost/SqFt | DIY? |
|---|---|---|---|---|
| Fiberglass Batt | R-3.2 | 11.9" | $4.56 | Yes |
| Blown-In Fiberglass | R-2.5 | 15.2" | $3.04 | Pro |
| Blown-In Cellulose | R-3.5 | 10.9" | $2.66 | Yes |
| Open-Cell Spray Foam | R-3.7 | 10.3" | $15.20 | Pro |
| Closed-Cell Spray Foam | R-6.5 | 5.8" | $30.40 | Pro |
| Mineral Wool Batt | R-3.3 | 11.5" | $5.70 | Yes |
| Mineral Wool Board | R-4.3 | 8.8" | $9.50 | Yes |
| Extruded Polystyrene (XPS) | R-5 | 7.6" | $6.84 | Yes |
| Expanded Polystyrene (EPS) | R-3.9 | 9.7" | $4.56 | Yes |
| Polyisocyanurate (Polyiso) | R-6 | 6.3" | $8.36 | Yes |
| Cotton Denim (Recycled) | R-3.5 | 10.9" | $7.60 | Yes |
| Sheep Wool | R-3.5 | 10.9" | $13.30 | Yes |
| Aerogel Blanket | R-10 | 3.8" | $114.00 | Yes |
| Vermiculite (Loose Fill) | R-2.1 | 18.1" | $3.80 | Yes |
Insulation Strategy for Zone 3
Zone 3 represents a transition from cooling-dominated to mixed climates, and insulation strategies must address both seasons effectively. The R-38 attic requirement can be met with approximately 12 inches of blown cellulose or 10 inches of fiberglass batts. Floor insulation at R-19 becomes important in this zone for homes with crawlspaces or raised foundations, as winter temperatures can drop low enough to create significant heat loss through uninsulated floors. Basement and crawlspace wall insulation at R-5 is introduced in this zone, reflecting the increasing importance of below-grade thermal protection. Air sealing the building envelope remains crucial, with particular attention to rim joists, sill plates, and penetrations through the building shell.
States in Climate Zone 3
The following states include areas that fall within DOE Climate Zone 3. Note that many states span multiple climate zones, so specific locations within a state may have different insulation requirements. Click any state to see the specific zones that apply and the complete insulation recommendations for each area.
Other Climate Zones
Compare insulation requirements across climate zones to understand how your location's needs compare to other regions. Each zone page includes complete R-value tables, state listings, and insulation strategies.