How Much Blown Insulation Do I Need, Insulation in the attic

How Much Blown Insulation Do I Need? A DIY Guide

Is your attic drafty in winter and sweltering in summer? Does your energy bill tell a similar story? It might be time to add blown-in insulation! But before you head to the store, you need to figure out how much insulation you’ll need. Let’s break down the calculations and help you get your project off to the right start.

Why Does the Amount of Insulation Matter?

  • Comfort: Adequate insulation helps keep your home consistently comfortable throughout the year.
  • Energy Savings: Stop heating and cooling the outdoors! Proper insulation lowers your energy bills by keeping temperature even throughout your home.
  • Investment: Getting the right amount of insulation maximizes the return on your investment for years to come.

How to Calculate Your Blown-In Insulation Needs

There are two main approaches. We’ll walk you through both:

Method 1: R-Value and Square Footage

  • Step 1: Measure Your Attic: Get the square footage by measuring the length and width, then multiplying them.
  • Step 2: Find Your Target R-Value: The R-value measures how well insulation resists heat flow. The U.S. Department of Energy has a handy chart ([invalid URL removed]) showing recommended R-values by climate zone.
  • Step 3: Use an Insulation Calculator: Plug in your square footage, desired R-value, and chosen insulation material (fiberglass, cellulose, etc.) into an online calculator. Try these:

Method 2: Desired Depth

  • Step 1: Measure Existing Insulation: If you have some and want to add more, measure its depth.
  • Step 2: Find Total Recommended Depth: Refer to the insulation’s packaging or the manufacturer’s website for the depth needed to achieve your desired R-value.
  • Step 3: Do the Math: Subtract existing depth (if any) from the total recommended depth. Then multiply this by your attic’s square footage to get cubic feet of insulation needed.
  • Step 4: Match to Product Specs: Check the insulation bag to see how many cubic feet it covers. Divide your total cubic feet by the bag’s coverage to get the number of bags.

Example: Your 1200 sq. ft. attic needs R-60. Your chosen cellulose insulation requires 15 inches of depth to achieve that. You’ll need 1500 cubic feet of insulation (1200 sq. ft. x 1.25 ft. depth). A bag of your insulation covers 40 cubic feet, so you’d need 37.5 bags – round up to 38.

Pro Tip:

It’s always a good idea to buy a little extra insulation to account for any uneven distribution or settling that may occur during installation.

Key Takeaways

  • Blown-in insulation is effective, but the right amount is crucial.
  • R-value recommendations depend on your local climate.
  • Online calculators simplify the process.
  • Always factor in the specific insulation material you’re using.

Important Considerations

  • DIY vs. Pro: While DIY is possible, professionals can accurately assess your needs and ensure even installation.
  • Air Sealing is Key: No amount of insulation will help if you have drafty areas. Air seal your attic before insulating.
  • Material Choice: Fiberglass, cellulose, and mineral wool all differ in density and coverage.


So, there you have it! With these simple steps, you can confidently tackle your blown insulation project like a pro. Remember, proper insulation not only keeps your home comfortable year-round but also helps save on energy costs in the long run. 


If you’re still unsure about how much blown insulation you need or need assistance with installation, don’t hesitate to reach out to us. Our team of experts is here to help you every step of the way.

Disclaimer: This blog post provides general guidance. Always consult product specifications and local codes. For complex projects, consider professional insulation installation.