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How to Install Blown-In Insulation

Pro Referral > Home Guides > Insulation > How to Install Blown-In Insulation
How to Install Blown-In Insulation

Adding insulation to your home can improve heating and cooling efficiency and make living areas more comfortable. Although the best time to insulate is during construction when the studs on exterior walls are exposed, it is possible and practical to add insulation to a finished home. Loose fill insulation, commonly comprised of wood fibers or “cellulose” is a great option for insulating a space with finished walls. Rather than take down existing plaster or drywall, small holes can be drilled in the exterior or interior wall surface so the material can be added to the wall cavities with a blower. This type of insulation is also good for attic applications and can be spread by hand in that setting as well as with a blower.

Materials Skill Level Estimated Time
• Tape Measure Intermediate 5 to 8 hours
• Drill
• Stud Finder
• Weighed String or Infared Thermometer
• Insulation Blower
• Protective Gear

Loose-fill insulation can be an irritant, so follow basic safety precautions when handling the material, such as wearing eye protection, a dust mask or respirator, gloves, and long sleeves and pants. You will need to rent an insulation blower and have a drill with a hole saw, along with a few tools on hand to help determine the best drilling locations such as a stud finder, tape measure, and a weighted string or infrared thermometer.

Installation Process

Follow the steps below to install blown-in insulation.

  1. 1.Determine Whether to Install from Inside or Outside

    When installing insulation with a blower the work can be done from indoors or outside. Decide which method makes the most sense for your application by considering whether it will be simpler to remove some of the siding and cut through the wall sheathing from the outside or to cut through the drywall inside and patch the holes after the job is done.

  2. 2.Locate the Height for Access Holes

    In addition to holes about 2” below the ceiling in each wall cavity, additional holes may be needed to accommodate fire blocking in some homes. The blocking will prevent insulation making it all the way to the bottom plate when blown in from above. If you are unsure if there is blocking between the studs in your walls, lower a weight on a string through the upper holes or use a stud finder to try to determine the location of blocking in each bay. If blocking is found, access holes will be needed below it in order to fill the lower cavity. You also can proceed with the installation from the top and later use an infrared thermometer to determine if there is a temperature disparity between the upper and lower portion of the wall, then drill holes and insulate the lower portion as needed.

  3. 3.Drill Access Holes

    If you are working from outside, remove the siding in the area of the access holes if possible. When installing from indoors, remove wall hangings and furnishings to prevent damage. Using a drill fitted with a hole saw, drill holes appropriately sized for the hose or nozzle of your insulation blower in the top of each bay between wall studs, as well as below fire blocking if needed.

  4. 4.Install the Insulation

    Use a two person team to run the nozzle and the hopper of the blower simultaneously. Locate the hopper outdoors, load it with loose-fill insulation and turn on the blower. Carry the hose to the installation site, insert the nozzle in the pre-drilled access holes, and switch the nozzle on to blow material into the cavity. It is important to slightly overfill each cavity since the insulation will settle over time, so continue filling until you feel slight pressure against the nozzle or a bit of material starts working out around the nozzle in the access hole. As the bay becomes full, angle the nozzle upward to fill the space above the access hole. Be sure to keep the hopper filled during operation to provide a steady supply of insulation.

  5. 5.Patch the Holes

    For exterior installations, patch the wall sheathing and/or siding as appropriate for the materials involved and reinstall siding that was removed. From inside, use mesh drywall tape and joint compound to cover the access holes and restore the wall surface and then prime and repaint as needed.

Level of Difficulty

Installing blown-in insulation requires more advanced skills than installing batts or rolls of insulation in order to locate, prepare, and patch the holes needed for the job, but is still only a moderately difficult project for most homeowners. The job requires an extra person to run the machine, and it can be dusty, messy, and even uncomfortable for individuals with asthma or respiratory issues, so it is important to take relevant safety precautions.


If installing insulation is a project that falls outside your area of expertise or is just a task you would rather leave to a pro, call in an experienced contractor to handle the job. The improvement in heating and cooling efficiency will make it worth the investment!

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