Insulation R-Value Guide: What R-Value Do I Need?

What Is R-Value?

R-value measures thermal resistance --- how well insulation resists heat flow. Higher R-values mean better insulation. An R-38 batt is approximately twice as effective at blocking heat transfer as an R-19 batt.

R-values are additive. If you have existing R-19 insulation in your attic and add R-19 on top, you get R-38 total. This makes it easy to upgrade existing insulation without removing what is already there.

Recommended R-Values by Climate Zone

Zone 1 (Southern Florida, Hawaii): Attic R-30 to R-49, Walls R-13, Floor R-13.

Zone 2 (Southern states: TX, LA, MS, AL, GA, SC): Attic R-30 to R-60, Walls R-13 to R-16, Floor R-13 to R-19.

Zone 3 (Mid-southern states: AR, TN, NC, OK): Attic R-30 to R-60, Walls R-13 to R-21, Floor R-19 to R-25.

Zone 4 (Mid-Atlantic, lower Midwest: VA, KY, MO, KS): Attic R-38 to R-60, Walls R-13 to R-21, Floor R-25 to R-30.

Zone 5 (Upper Midwest, Northeast: IL, IN, OH, PA, NY, NJ, CT): Attic R-38 to R-60, Walls R-13 to R-21, Floor R-25 to R-30.

Zone 6-7 (Northern states: MN, WI, MI, ME, VT, NH, MT): Attic R-49 to R-60, Walls R-21 to R-28, Floor R-25 to R-30.

Use our insulation calculator to determine exactly how much material you need based on your target R-value and area.

Insulation Types Compared

Fiberglass batts: R-3.1 to R-3.4 per inch. Cost: $0.50-$1.50/sq ft. The most common DIY insulation. Available in pre-cut widths for standard framing. Best for open wall cavities and attic floors.

Blown-in cellulose: R-3.2 to R-3.8 per inch. Cost: $1.00-$2.50/sq ft installed. Made from recycled newspaper. Fills irregular cavities better than batts. Excellent for retrofitting existing walls and topping off attic insulation.

Blown-in fiberglass: R-2.2 to R-2.7 per inch. Cost: $1.00-$2.00/sq ft installed. Similar to cellulose but does not absorb moisture. Good for attics where moisture is a concern.

Open-cell spray foam: R-3.5 to R-3.7 per inch. Cost: $1.00-$2.00/sq ft. Expands to fill cavities completely. Good sound insulation. Must be covered with drywall (fire code).

Closed-cell spray foam: R-6.0 to R-7.0 per inch. Cost: $2.00-$4.50/sq ft. The highest R-value per inch. Also acts as air and moisture barrier. Adds structural rigidity. Best for basements, crawl spaces, and thin wall assemblies where space is limited.

Energy Savings from Insulation

The Department of Energy estimates that proper insulation saves 10-50% on heating and cooling costs, depending on your current insulation level and climate. For an average US home spending $2,000/year on energy, that is $200-$1,000 in annual savings.

Attic insulation provides the best return on investment because heat rises --- an under-insulated attic is responsible for 25-30% of a home's total heat loss. Upgrading from R-11 to R-38 in the attic typically pays for itself in 2-4 years.

Wall insulation is the second priority. Uninsulated exterior walls account for 35% of heat loss. Even adding R-13 batts to previously empty wall cavities dramatically improves comfort and reduces energy bills.

DIY Insulation Tips

Attic insulation is the easiest DIY insulation project. Lay fiberglass batts perpendicular to existing insulation, or rent a cellulose blowing machine ($50-$100/day from most home centers --- often free with purchase of 20+ bags).

Wear proper PPE: N95 respirator mask, safety goggles, long sleeves, gloves, and long pants when handling fiberglass. Cellulose is less irritating but still requires respiratory protection.

Air seal before insulating. Caulk and foam around all penetrations (electrical boxes, plumbing pipes, recessed lights, attic hatch) before adding insulation. Air leaks can reduce insulation effectiveness by 25-40%.

Where to Insulate First for the Best Return

Not all insulation upgrades pay back equally. The attic is almost always the highest-return place to start, because heat rises and a poorly insulated attic bleeds money year-round. Bringing attic insulation up to current recommended levels is the single most cost-effective improvement in most homes.

After the attic, focus on air leaks and then walls, floors over unconditioned space, and basement or crawlspace surfaces. Insulating rim joists and sealing the basement band is cheap and surprisingly effective at stopping drafts.

Walls are harder and costlier to insulate in an existing home, since it usually means blowing insulation into closed cavities. It still helps, but the attic and air sealing should come first for the best dollar-per-comfort return.

Air Sealing Works With Insulation

Insulation slows heat transfer, but it does not stop air from leaking through gaps. A home can be heavily insulated and still feel drafty and cost a fortune to heat if it leaks air around penetrations, top plates, recessed lights, and the attic hatch.

Seal first, then insulate. Caulk and foam the small gaps, weatherstrip the attic hatch, and address the biggest leaks before adding insulation on top. Air sealing is inexpensive and multiplies the value of the insulation you already have.

A blower-door test from an energy auditor pinpoints exactly where a home leaks. Many utilities offer rebates that cover part of the cost of an audit and the resulting air-sealing and insulation work.

Frequently Asked Questions

What R-value do I need for my attic? Most regions call for roughly R-38 to R-60 in the attic. Colder climates need the higher end. Check your climate zone recommendation before buying.

Can I add new insulation over old? Yes. You can lay new batts or blow loose-fill over existing attic insulation as long as the old material is dry and not moldy. Do not compress it, since compression reduces R-value.

Does more insulation always save money? Up to the recommended level, yes. Beyond that, returns shrink and the payback stretches out. Hitting the recommended R-value and air sealing is the sweet spot. Our insulation calculator estimates the material you need for your target R-value.

Matching Insulation Type to the Application

R-value measures resistance to heat flow, but the highest R-value is not automatically the right choice for every part of your home. The best material depends on the cavity, the moisture conditions, and your budget. Fiberglass batts are inexpensive and DIY-friendly for open stud walls and accessible attic joists, while blown-in cellulose or fiberglass excels in existing closed walls and irregular attic spaces where batts would leave gaps.

Spray foam occupies the premium end and serves a different purpose: closed-cell foam delivers a high R-value per inch and doubles as an air and vapor barrier, making it ideal for rim joists, cathedral ceilings, and tight spaces where every inch counts. Its higher cost is justified where air sealing and moisture control matter as much as raw R-value, such as basements and crawl spaces prone to humidity.

Rigid foam board rounds out the toolkit for continuous insulation over sheathing, under slabs, and on foundation walls, where it interrupts the thermal bridging that occurs through studs and framing. Remember that achieving the labeled R-value depends entirely on correct installation — compressed batts, gaps around obstructions, and voids behind wiring all degrade performance. Pairing the right product with careful air sealing delivers far better real-world comfort and energy savings than simply chasing the biggest R-number on the label.