The DOE recommends R-38 to R-60 for most U.S. attics depending on climate zone, roughly 12–18 inches of blown-in fiberglass or cellulose. The correct figure is zone-specific: southern zone 1–2 homes need R-30 to R-38; northern zone 5–7 homes need R-49 to R-60. Attic insulation is one of the highest-return energy efficiency upgrades because the attic floor is the primary path for heat gain and loss in most homes.
This guide is a specialized spoke of our comprehensive HVAC System Sizing & Cost Guide→. Check it out for all calculations, material sizing, and industry standards.
The attic floor is where most homes lose the most heating and cooling energy. Heat moves through the path of least resistance, and an under-insulated attic creates a large, low-resistance path between conditioned living space and unconditioned attic air. In summer, attic temperatures regularly exceed 130°F in many U.S. climates; without adequate insulation on the floor, that heat conducts directly into ceiling assemblies and living areas.
The DOE recommends specific R-value targets by climate zone, not a single national number. Whether your home needs R-30 or R-60 depends on where you live. This article covers how to determine what you have, what you need, and what it costs to get there.
The DOE recommends R-38 to R-60 for most U.S. attics, or about 12–18 inches of blown-in material. Fiberglass blown-in costs $1–$1.8/SF installed; cellulose costs $1.2–$2/SF. Zone 1–2 (Florida, Gulf Coast, Southwest): R-30 to R-38. Zones 3–4 (Mid-Atlantic, Midwest): R-38 to R-49. Zones 5–7 (Northeast, northern Midwest): R-49 to R-60. Check your zone at energy.gov.
R-value recommendations per U.S. DOE Insulation Recommendations by Zone. Cost ranges from Meazora 2026 installer data.
The Department of Energy publishes recommended attic insulation R-values by climate zone. These are minimum recommendations for existing homes that are under-insulated:
To confirm your zone, enter your ZIP code at energycodes.gov or the DOE's insulation page at energy.gov/energysaver/insulation. The target for your zone is the total R-value after adding new insulation over whatever you already have. To identify where your home is losing energy, check if a home energy audit is worth it.
Grab a tape measure, a bright flashlight, and a dust mask. Work from the attic access hatch or pull-down stairs: you don't need to walk the full attic to get a useful assessment.
Blown-in fiberglass ($1–$1.8/SF installed): The most common professional installation for attic floor insulation. Machine-blown fiberglass fills irregular spaces better than batts and achieves consistent R-value per inch (approximately R-2.5 per inch). Does not settle significantly over time. Professional installation recommended for achieving uniform coverage.
Blown-in cellulose ($1.2–$2/SF installed): Made from recycled paper treated with borate for fire and pest resistance. Achieves approximately R-3.5 per inch. Cellulose settles over time, typically 15–20% within the first year, which is accounted for by installing to a higher initial depth. Per NAIMA, properly installed and settled cellulose still meets its rated R-value. DIY-friendly with rented blower equipment; available at most home centers.
Spray foam ($6–$12/SF): Provides both air sealing and insulation in one application. Open-cell spray foam achieves approximately R-3.5 per inch; closed-cell achieves R-6 to R-7 per inch. The primary use case in attics is air sealing penetrations and bypasses rather than whole-attic coverage: the cost per SF makes it impractical for full attic floor coverage in most situations. Requires professional installation.
Start with your attic's square footage (length × width, minus any obstructions). Then check the coverage table on the insulation bag for the target R-value. A typical bag of blown-in fiberglass covers:
For a 1,500 SF attic targeting R-38 from zero, you'll need approximately 45–50 bags of blown-in fiberglass. If you already have R-19 and are adding to reach R-38, you're buying for the difference, approximately half that quantity. Order 10% extra to account for settling and irregular areas.
Use our remodeling calculators to estimate bag counts and total material cost based on your attic's square footage and target R-value.
To maintain absolute calculation integrity and trust, the structural lifespans, standard sizes, and pricing models in this guide are gathered from governing construction authorities and verified trade standards.
Mauricio L. is a software developer who loves working with his hands. He built Meazora because he was tired of online calculators that exist just to capture your email and phone number. Every calculator here runs completely in your browser to keep your planning private, fast, and simple.
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