Attic Insulation Calculator

Stop Burning Money: The Ultimate Guide to Attic Insulation

Did you know that 25% of your home's heat is lost through the roof? In the winter, warm air rises into your attic and escapes. In the summer, the sun bakes your roof shingles, turning your attic into an oven that radiates heat down into your living space. The only defense against this thermal assault is insulation. Adding insulation to your attic is one of the highest ROI (Return on Investment) home improvement projects you can do, often paying for itself in energy savings within 2-3 years.

Understanding R-Value

Insulation is measured by its resistance to heat flow, known as R-Value. The higher the R-Value, the better it insulates.
- R-30: Minimum standard for warm climates (Florida, Texas).
- R-38 to R-49: Recommended for most temperate zones (Midwest, Mid-Atlantic).
- R-60: Recommended for very cold climates (Northern US, Canada).

Types of Blown-In Insulation

This calculator focuses on loose-fill (blown-in) insulation, which is the most common DIY method for retrofitting attics.

1. Fiberglass (White/Pink Fluff):
- Made from spun glass fibers.
- R-Value per inch: ~2.5 to 2.8.
- Pros: Doesn't settle much over time, fire-resistant, moisture-resistant.
- Cons: Can be itchy to work with, lower R-value per inch than cellulose.

2. Cellulose (Grey Paper):
- Made from recycled newspapers treated with borate (fire retardant).
- R-Value per inch: ~3.2 to 3.8.
- Pros: Higher R-value per inch, better sound dampening, green product.
- Cons: Settles significantly (up to 20%) over time, very dusty during installation.

How Deep Should It Be?

To achieve your target R-Value, you need a specific depth of material.
- To get R-38 with fiberglass, you generally need about 13-14 inches thick.
- To get R-38 with cellulose, you need about 10-12 inches thick (initially installed deeper to account for settling).
This calculator gives you a general depth estimate based on fiberglass averages (3.2 R/inch for high-density blown products).

Installation Tips for DIYers

Thinking of renting a blower machine from Home Depot or Lowe's?
1. Air Seal First: Insulation keeps heat in, but it doesn't stop air movement. Use spray foam to seal gaps around light fixtures, plumbing stacks, and electrical wires before you bury them in insulation.
2. Don't Block Soffit Vents: Your attic needs to breathe. If you cover the vents at the edge of the roof (eaves), moisture will get trapped and cause mold. Install "baffles" or "rafter vents" to keep an air channel open.
3. Wear Protection: A respirator (N95) is mandatory. Goggles and long sleeves are highly recommended to avoid skin irritation.

Calculating Bags Needed

Every bag of insulation has a "coverage chart" printed on it. This chart tells you exactly how many bags are required for 1,000 sq ft at various R-values. Our calculator provides an estimate based on standard industry averages (typically 1 bag covers ~40-50 sq ft at R-19). Always check the specific bag you are buying for the final count.