Climate Zone 4 — Mixed
Zone 4 is the true mixed climate zone where heating and cooling loads are roughly balanced over the course of a year. Major cities in this zone include Washington DC, St. Louis, Seattle, and much of the mid-Atlantic and Pacific Northwest. This is the first zone where the DOE recommends continuous exterior wall insulation in addition to cavity insulation, reflecting the increased importance of thermal bridging reduction. Buildings in Zone 4 benefit significantly from a comprehensive insulation approach that addresses the building envelope from foundation to ridge.
Zone 4 Climate Data
R-Value Requirements for Zone 4
The table below lists the DOE recommended insulation R-values for every building component in Climate Zone 4 (Mixed). 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-49 | View insulation options → |
| Wall Cavity | R-13 | View insulation options → |
| Wall Continuous | R-5 | View insulation options → |
| Floor | R-25 | View insulation options → |
| Basement Wall | R-10 | View insulation options → |
| Crawlspace | R-10 | View insulation options → |
| Cathedral Ceiling | R-38 | View insulation options → |
| Garage Ceiling | R-30 | View insulation options → |
Insulation Thickness by Type for Zone 4 Attic (R-49)
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-49 recommendation for Zone 4 attics, along with the estimated material cost per square foot.
| Insulation Type | R/Inch | Thickness Needed | Cost/SqFt | DIY? |
|---|---|---|---|---|
| Fiberglass Batt | R-3.2 | 15.3" | $5.88 | Yes |
| Blown-In Fiberglass | R-2.5 | 19.6" | $3.92 | Pro |
| Blown-In Cellulose | R-3.5 | 14" | $3.43 | Yes |
| Open-Cell Spray Foam | R-3.7 | 13.2" | $19.60 | Pro |
| Closed-Cell Spray Foam | R-6.5 | 7.5" | $39.20 | Pro |
| Mineral Wool Batt | R-3.3 | 14.8" | $7.35 | Yes |
| Mineral Wool Board | R-4.3 | 11.4" | $12.25 | Yes |
| Extruded Polystyrene (XPS) | R-5 | 9.8" | $8.82 | Yes |
| Expanded Polystyrene (EPS) | R-3.9 | 12.6" | $5.88 | Yes |
| Polyisocyanurate (Polyiso) | R-6 | 8.2" | $10.78 | Yes |
| Cotton Denim (Recycled) | R-3.5 | 14" | $9.80 | Yes |
| Sheep Wool | R-3.5 | 14" | $17.15 | Yes |
| Aerogel Blanket | R-10 | 4.9" | $147.00 | Yes |
| Vermiculite (Loose Fill) | R-2.1 | 23.3" | $4.90 | Yes |
Insulation Strategy for Zone 4
Zone 4 marks the first zone where the DOE recommends both cavity and continuous exterior wall insulation. The R-13 plus R-5 wall recommendation addresses thermal bridging through framing members, which can reduce the effective whole-wall R-value by 15-25 percent in standard construction. The attic requirement jumps to R-49, requiring 14-16 inches of blown insulation. Floor insulation at R-25 and basement wall insulation at R-10 reflect the significant heating loads in this mixed climate. Building science considerations become more complex in Zone 4 because both heating and cooling seasons create vapor drives in opposite directions. Proper vapor retarder placement and selection of vapor-permeable exterior insulation materials are important to allow wall assemblies to dry in both directions.
States in Climate Zone 4
The following states include areas that fall within DOE Climate Zone 4. 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.