How to Insulate an Attic

By
Lee Wallender
Lee Wallender
Lee Wallender

Lee has over two decades of hands-on experience remodeling, fixing, and improving homes, and has been providing home improvement advice for over 13 years.

Learn more about The Spruce's Editorial Process
Updated on 12/19/22
Reviewed by
Kelly Bacon
Kelly Bacon
Reviewed by Kelly Bacon

Kelly Bacon is a licensed general contractor with over 40 years of experience in construction, home building and remodeling, and commercial building. He is a member of The Spruce Home Improvement Review Board.

Learn more about The Spruce's Review Board
A light and airy bedroom in an attic with natural wood beams, plants, and a fireplace.

 

Andreas von Einsiedel / Getty Images

Project Overview
  • Working Time: 2 hrs
  • Total Time: 8 hrs
  • Yield: 1,300 square feet of attic
  • Skill Level: Advanced
  • Estimated Cost: $800 to $1,000

If you had to pick one energy-saving tactic for your home, what would it be? Caulking the windows? Thermal insulating curtains? Wall insulation and replacement windows might be a natural thought, too.

It's easy to forget about that large energy-wasting surface over your head: the ceiling and attic. According to Energy Star, the best way to save energy in a home is by insulating the attic. This helps you to maintain the temperature of the living space below while you save on energy costs.

Codes, Regulations, and Permits

While it is not common, some communities may require a building permit before adding insulation to an unfinished attic. Check with your local permitting agency before installing any type of attic insulation.

Insulation Rolls or Batts vs. Blown-In Insulation

Though blown-in insulation offers a slight advantage for do-it-yourselfers, it helps to consider both methods to determine which one is best for you.

Fiberglass Rolls or Batts

Ceiling fiberglass insulation comes in rolls up to 25 feet long. In batt form, the insulation is in pieces 4 feet long. Both are the width of joist cavities. Batts can be obtained in thicker form than rolls, for up to an R-49 thermal value.

Pros

  • Saves on cost of blower machine

  • Continuous insulation, no gaps

Cons

  • Laborious to install

  • Difficult when the attic has many obstacles

Blown-In Insulation

Fiberglass or cellulose loose-fill insulation is run through a blower machine located on the ground level, with a long hose reaching into the attic. The operator in the attic shoots the insulation throughout the attic and into the cavities, up to a certain depth.

Blown-in insulation requires more preparation time than with batts or rolls. But once the attic is ready, it is possible to cover a medium-size attic space in an hour or two.

Pros

  • Requires very little climbing or time spent in the attic with the blower hose

  • Easy to fill around wires and vents

Cons

  • Blower machine rental cost

  • Easy to miss areas when shooting from a distance

Safety Considerations

Insulating your attic requires you to frequently go in and out of the attic. You'll also be moving around the entire space. Use a step ladder held by a partner for accessing the attic. Within the attic, walk only on joists or on 3/4-inch plywood or OSB boards laid across the joists. Watch your head to avoid bumping on rafters, and be especially aware of roofing nails piercing through the roof deck. Suit yourself up with a full range of personal protection gear: breathing protection, eye protection, long sleeves, pants, and gloves.

Finally, remember that attics are often dark places. Set up a portable light source in the attic so you can see everything while you work.

Warning

Attics can become very hot. If the outside temperature is 100 degrees Fahrenheit, it is not uncommon for the attic to reach 140 to 150 degrees Fahrenheit—far too hot to safely or comfortably work in the attic. Spring or fall tend to be the best seasons for this project.

8 Before and After Attic Makeovers to Inspire Your Own

What You'll Need

Equipment / Tools

  • Insulation blower machine
  • Extension cord
  • Utility knife
  • Ladder
  • NIOSH or MSHA approved breathing protection
  • Straight edge ruler
  • Caulking gun
  • Light

Materials

  • Blown-in fiberglass insulation
  • Drop cloths
  • Attic hatch shield
  • Recessed light covers (if applicable)
  • Caulk

Instructions

In this tutorial, we've provided the instructions for adding blown-in insulation to your attic.

  1. Calculate How Much Insulation You Need

    Measure the length and width of your home to arrive at its area. Next, calculate the desired depth of the blown-in insulation.

    Depth of Expanding Fiberglass Insulation R-Value
    7 inches R-19
    9 inches R-25
    11 inches R-30
    13 inches R-38
    15 inches R-44
    17 inches R-49
    20 inches R-60

  2. Shield Uninsulated Areas

    Because blown-in insulation covers nearly the entire attic, areas that cannot be covered with insulation should be shielded. This includes recessed lights, vents, exhaust fans, and the attic hatch.

    Tip

    It's very important to keep soffit vents from being blocked. Air flow is vital to keeping the attic cool and insulation dry.

  3. Seal the Attic and Add Measuring Strips

    Identify all areas of the attic that will emit air and seal them with caulk. Staple measuring strips on vertical areas, so that you will later know how deep to blow the insulation.

  4. Rent the Correct Insulation Blower

    To blow fiberglass insulation, you will need a certain type of blower for expanding the insulation. This blower shreds packets of compacted fiberglass insulation. Blowers for loose-fill cellulose insulation may not work.

    Fact

    Cellulose insulation is made from recycled paper products and uses up to 85-percent recycled materials. Cellulose insulation is rendered inflammable by the addition of fire-retarding borates.

  5. Start the Blower Machine

    Two people are required: one in the attic with the blower hose and one on the ground feeding insulation into the machine.

    Hook up the hose to the machine. Move the nozzle end of the hose up through the attic hatch and into the attic. When the person in the attic is ready, the person operating the machine should plug the machine in, then turn it on.

    Tip

    Use two-way radios, text messaging, or phones to communicate between the ground and the attic.


  6. Blow the Insulation Into the Attic

    Stand in a central location and blow insulation to the outer-most areas of the attic to the correct depth. Keep blowing toward the center of the attic until the entire attic is covered to the correct depth.

When to Call a Professional

Renting the insulation blower and transporting it to your house, along with many bags of blown-in insulation, can be a project all by itself. So, too, can be the preparation phase. Call an insulation company to blow in your insulation if these projects seem too difficult.

Should You Remove Old Insulation?

If your current loose-fill insulation is moldy, it needs to be removed. Hire a company for this, rent a machine specifically for the job, or remove the old insulation by hand. Insulation blowers typically cannot be reversed to suction out old insulation.