Home Insulation Guide — R-Values Explained & How Much You Need
Understand R-values, insulation types, and how much insulation your home needs. Covers fiberglass, cellulose, spray foam, and mineral wool with cost comparisons and energy savings.
Insulation is the invisible hero of home comfort and energy efficiency. Proper insulation can reduce heating and cooling costs by 20-40%, yet the Department of Energy estimates that 90% of US homes are under-insulated. Understanding R-values and insulation types helps you make smart upgrade decisions.
What Is R-Value?
R-value measures thermal resistance — the ability of a material to resist heat flow. Higher R-values mean better insulation. R-value is additive: R-19 wall insulation plus R-5 exterior sheathing equals R-24 total. The required R-value depends on your climate zone, which part of the house you are insulating, and local building codes.
Recommended R-Values by Climate Zone
The US Department of Energy divides the country into climate zones 1-7. Zone 1-2 (hot climates like FL, TX): Attic R-30 to R-60, Walls R-13 to R-21. Zone 3-4 (mixed climates like TN, VA): Attic R-38 to R-60, Walls R-13 to R-21. Zone 5-7 (cold climates like NY, MN, ME): Attic R-49 to R-60, Walls R-21 to R-30.
Attics should always have the highest R-value because heat rises — an under-insulated attic is like leaving a window open in winter. Adding attic insulation offers the best return on investment of any insulation upgrade, often paying for itself in 2-4 years.
Insulation Types Compared
Fiberglass batts (R-3.2/inch, $0.50-$1.00/sq ft): The most common and affordable option. Easy to install for DIYers. Best for standard stud cavities in walls and floors. Downsides: gaps and compression reduce effectiveness significantly.
Blown-in cellulose (R-3.5/inch, $1.00-$1.50/sq ft): Made from recycled paper treated with fire retardant. Excellent for attics and retrofitting existing walls. Fills irregular spaces better than batts. Naturally resistant to pests and mold.
Spray foam — open cell (R-3.7/inch, $1.00-$2.00/sq ft): Expands to fill all gaps and cracks. Good for walls, crawlspaces, and rim joists. Also acts as an air barrier. Requires professional installation. Spray foam — closed cell (R-6.5/inch, $2.00-$4.00/sq ft): The highest R-value per inch. Also a vapor barrier. Adds structural strength. Best for limited-space applications.
Where to Insulate First (Priority Order)
1. Attic floor — biggest temperature difference, easiest to access. 2. Exterior walls — largest surface area losing energy. 3. Crawlspace/basement — prevent cold floors and moisture issues. 4. Rim joists — small area but major air leakage point. 5. Ductwork — prevent conditioned air loss in unconditioned spaces.
Cost vs. Savings
Adding R-38 blown cellulose to an uninsulated 1,500 sq ft attic costs $1,500-$3,000 professionally installed and saves $300-$600/year on energy bills — a 3-5 year payback. Insulating exterior walls costs $3,000-$8,000 for a typical home and saves $200-$400/year. Use our Insulation Calculator to determine exact quantities, and our HVAC BTU Calculator to see how insulation affects your heating and cooling loads.