Installing Insulation in Existing Walls

By Dave Donovan
Thanks to modern equipment and advanced loose-fill insulating materials, installing insulation between walls that are already finished is something that can be accomplished in just a few hours.
Of course, this is a job that can pose some difficulties for the casual do-it-yourselfer and it might be best left in the hands of a professional, but if you’ve worked with this type of equipment before — or you’re interested in learning — you should be able to handle the job although it might take longer than expected.
Once a home is finished, it is unrealistic to pull the existing drywall off the wall and insert traditional batting insulation within the cavity. The best method of adding insulation to a finished wall is to use blown insulation.
This material is projected into the cavity through a hole until the cavity is completely filled. The most challenging aspect of this job is making sure that every nook and crevice is filled with insulation. In areas where plumbing pipes or ductwork may be involved, several holes may need to be created so the fill can reach all of the necessary areas.
In many cases, it is easier to perform this job from the outside of the house, but it will require you to remove siding in order to gain access to the walls.
Tools and Materials
  • Hammer
  • Stud finder
  • Ladder
  • Blower equipment (including hose and nozzle)
  • Power drill with bits and hole saw
  • Saber saw
  • Pry bar (for wood siding)
  • Zip tool (for vinyl siding)
  • Wood glue
  • Plastic plugs
  • Loose-fill insulation

Safety Tip

Working with loose-fill insulation poses the same risks as working with rolls of insulation, so it is important to wear safety gear like eye goggles, work gloves, a long-sleeved shirt and a NIOSH-approved breathing respirator.
Step 1: Remove the Siding
On the exterior of the house, measure up approximately four feet from the floor line and start removing strips of siding. Working at four-foot intervals, use the pry bar and hammer to help you loosen and remove the siding if it is made out of wood. If the siding is vinyl, separate the seam and run a zip tool along it to free it.
Step 2: Find the Studs
Run a stud finder along the wall to determine where the wall studs are located. Mark the location of the studs so you know where you can safely drill your access holes.
Step 3: Turn Off the Electricity to the Circuits in the Wall
If the wall has electrical receptacles or other circuits running through it, you need to make sure all of the power is off in the wall before you start cutting. If you leave the power on and you accidentally nick or cut a wire, you can cause a dead short which may damage your equipment.
Step 4: Drill the Access Holes
Use a drill with a hole saw or a saber saw (with a pre-drilled pilot hole) to cut out your access holes between the studs. The size of the holes should be slightly larger than the dimension of the nozzle on the blower equipment.
Step 5: Prepare the Blower According to Instructions
Each blower has its own specifics when it comes to loading the hopper and using the machine, so check the manufacturer’s instructions to prevent a problem down the line.
Step 6: Start Blowing In the Insulation
Slide the blower’s nozzle into the access hole and turn the machine on. Fill the cavity with insulation, then move on to the next bay. As stated earlier, some bays may require you to make more than one access hole if there are obstructions in the wall.
Step 7: Install the Plugs
Plug each access hole using the appropriate sized plastic plug. If necessary, use glue to help keep the plug in place and then replace the siding. Move on to the next four-foot span of siding and perform the steps again.
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