Attic Insulation
The attic is the single most important location for insulation in most buildings. Because hot air rises, the attic represents the greatest source of heat loss in winter. In summer, the sun beating down on the roof can heat the attic space to 150 degrees Fahrenheit or more, making attic insulation critical for reducing cooling loads as well. The good news is that attic insulation is usually the most accessible and least expensive insulation to install or upgrade. Blown-in cellulose or fiberglass can be applied to any depth over existing insulation, and DIY-friendly blower machines are available for rental at most home improvement stores. Before adding attic insulation, always air seal the attic floor first. Sealing gaps around light fixtures, plumbing penetrations, duct boots, and the top plates of interior walls prevents warm, moisture-laden air from bypassing the insulation and condensing in the cold attic space. Proper ventilation from soffit to ridge must be maintained by installing baffles before blowing insulation.
Attic R-Value Requirements by Climate Zone
The table below shows the DOE recommended R-value for attic insulation in each climate zone. Click on any zone to see detailed insulation type comparisons with thickness and cost estimates specific to the attic in that climate zone.
| Climate Zone | Zone Name | Required R-Value | Details |
|---|---|---|---|
| Zone 1 | Hot-Humid | R-30 | Compare insulation types → |
| Zone 2 | Hot | R-38 | Compare insulation types → |
| Zone 3 | Warm | R-38 | Compare insulation types → |
| Zone 4 | Mixed | R-49 | Compare insulation types → |
| Zone 5 | Cool | R-49 | Compare insulation types → |
| Zone 6 | Cold | R-60 | Compare insulation types → |
| Zone 7 | Very Cold | R-60 | Compare insulation types → |
| Zone 8 | Subarctic | R-60 | Compare insulation types → |
Recommended Insulation Types for Attic
The following insulation types are specifically recommended for attic applications based on their material properties, moisture resistance, fire rating, and installation characteristics. While other insulation types can technically be used, these options provide the best combination of performance and practicality for this specific building component.
| Insulation Type | R/Inch | Cost/SqFt/R | Moisture | DIY |
|---|---|---|---|---|
| Fiberglass Batt | R-3.2 | $0.12 | Low | Yes |
| Blown-In Fiberglass | R-2.5 | $0.08 | Low | Pro |
| Blown-In Cellulose | R-3.5 | $0.07 | Moderate | Yes |
| Mineral Wool Batt | R-3.3 | $0.15 | High | Yes |
| Expanded Polystyrene (EPS) | R-3.9 | $0.12 | Moderate | Yes |
| Polyisocyanurate (Polyiso) | R-6 | $0.22 | Moderate | Yes |
| Cotton Denim (Recycled) | R-3.5 | $0.20 | Low | Yes |
| Sheep Wool | R-3.5 | $0.35 | Very High | Yes |
| Vermiculite (Loose Fill) | R-2.1 | $0.10 | Low | Yes |
Thickness Required by Insulation Type (Zone 5, R-49)
Using Zone 5 as a representative example, the table below shows how much of each insulation type is needed to achieve the DOE recommendation. The attic has a typical cavity depth of 16 inches, so insulation types that require more than this thickness will need deeper framing, additional layers, or a combination of insulation approaches.
| Insulation Type | R/Inch | Thickness Needed | Fits Cavity | Cost/1000 SqFt |
|---|---|---|---|---|
| Fiberglass Batt | R-3.2 | 15.3" | Yes | $5,880 |
| Blown-In Fiberglass | R-2.5 | 19.6" | No | $3,920 |
| Blown-In Cellulose | R-3.5 | 14" | Yes | $3,430 |
| Open-Cell Spray Foam | R-3.7 | 13.2" | Yes | $19,600 |
| Closed-Cell Spray Foam | R-6.5 | 7.5" | Yes | $39,200 |
| Mineral Wool Batt | R-3.3 | 14.8" | Yes | $7,350 |
| Mineral Wool Board | R-4.3 | 11.4" | Yes | $12,250 |
| Extruded Polystyrene (XPS) | R-5 | 9.8" | Yes | $8,820 |
| Expanded Polystyrene (EPS) | R-3.9 | 12.6" | Yes | $5,880 |
| Polyisocyanurate (Polyiso) | R-6 | 8.2" | Yes | $10,780 |
| Cotton Denim (Recycled) | R-3.5 | 14" | Yes | $9,800 |
| Sheep Wool | R-3.5 | 14" | Yes | $17,150 |
| Aerogel Blanket | R-10 | 4.9" | Yes | $147,000 |
| Vermiculite (Loose Fill) | R-2.1 | 23.3" | No | $4,900 |
Construction Notes
Attic insulation is typically installed between and over ceiling joists (2x6, 2x8, 2x10, or 2x12) on the attic floor. In new construction, the cavity can be filled and additional insulation layered on top perpendicular to the joists. Loose-fill blown insulation is the most common method for achieving high R-values in attics because it can be applied to any depth. When adding insulation to an existing attic, do not compress existing insulation; instead add new material on top. Ensure that soffit vents are not blocked and install baffles to maintain airflow from soffit to ridge. The attic is typically the single most cost-effective location to add insulation because heat rises and the attic represents the largest area of heat loss in most homes.
Other Building Components
Browse insulation requirements and installation guidance for other building components.