Insulation Calculator
A 1,200 sq ft attic in Climate Zone 5 needs R-49 insulation, requiring approximately 24 rolls of R-49 unfaced fiberglass batts (15-inch width, 50 sq ft per roll). Materials cost $430-$720. Wall insulation for a 1,500 sq ft home needs about 1,850 sq ft of R-13 batts at $350-$600.
Insulation Calculator
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How to Calculate Insulation
Measure the area to insulate (length x width for attics, wall height x perimeter for walls). Match R-value to your climate zone, then divide total area by the coverage per package.
| Climate Zone | States (examples) | Attic R-Value | Wall R-Value | Floor R-Value |
|---|---|---|---|---|
| 1-2 (Hot) | FL, TX, AZ, HI | R-30 to R-49 | R-13 | R-13 |
| 3 (Warm) | GA, AL, MS, SC | R-30 to R-60 | R-13 to R-15 | R-19 |
| 4 (Mixed) | VA, TN, NC, MO | R-38 to R-60 | R-13 to R-15 | R-19 to R-25 |
| 5 (Cold) | NY, PA, OH, IL | R-49 to R-60 | R-13 to R-21 | R-25 to R-30 |
| 6-7 (Very Cold) | MN, WI, ME, MT | R-49 to R-60 | R-21 | R-25 to R-30 |
| Insulation Type | R-Value per Inch | Cost per sq ft | Best For |
|---|---|---|---|
| Fiberglass batt | R-3.2 | $0.30-$0.80 | Walls, attics (standard) |
| Blown fiberglass | R-2.5 | $0.50-$1.00 | Attic topping, retrofit |
| Blown cellulose | R-3.5 | $0.40-$0.80 | Attic, dense-pack walls |
| Spray foam (open) | R-3.7 | $1.00-$1.75 | Walls, crawlspaces |
| Spray foam (closed) | R-6.5 | $1.50-$3.50 | Rim joists, high-R needs |
| Rigid foam (XPS) | R-5.0 | $0.75-$1.50 | Basement, exterior |
| Mineral wool batt | R-3.3 | $0.80-$1.50 | Fire-rated walls, sound |
Tips
- Never compress insulation to fit; compression reduces R-value significantly
- Unfaced batts are used for second layers; faced batts have vapor barrier for first layer
- Seal all air leaks with caulk and foam before installing insulation for maximum effectiveness
- Attic insulation should be continuous and level, covering the top plates of walls
- Wear long sleeves, gloves, goggles, and N95 mask when handling fiberglass insulation
Frequently Asked Questions
What R-value insulation do I need?
It depends on your climate zone and location in the home. Attics need R-30 (south) to R-60 (north). Walls need R-13 to R-21. Floors over unheated spaces need R-19 to R-30. Check the DOE climate zone map for your area.
How many rolls of insulation do I need for an attic?
Divide your attic square footage by the roll coverage (typically 40-80 sq ft per roll depending on width and R-value). A 1,200 sq ft attic with R-38 batts at 50 sq ft per roll needs 24 rolls.
How much does attic insulation cost?
DIY fiberglass batt insulation costs $0.30-$0.80 per sq ft. Blown-in professionally installed runs $1-$2.50 per sq ft. For a 1,200 sq ft attic, expect $360-$960 DIY or $1,200-$3,000 professionally installed.
Can I add insulation on top of existing insulation?
Yes, you can add unfaced batts or blown insulation over existing insulation to increase R-value. Never add faced insulation over existing, as double vapor barriers trap moisture. Check that existing insulation is dry and mold-free first.
What is the most effective insulation type?
Closed-cell spray foam has the highest R-value per inch (R-6.5) and also acts as an air and vapor barrier. However, it costs 3-5x more than fiberglass batts. For most homes, fiberglass batts or blown cellulose offer the best value.
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