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How to Blow in Insulation

Blowing Insulation Into Existing Walls

Have an old house without insulation? Don’t despair.

Thread a blower hose into a hole in the wall.

You can add insulation to your exterior walls—without the cost and inconvenience of removing your existing drywall—by blowing cellulose fibers between your wall studs.

Cellulose is a popular blown-in insulation material because its small particles fill in the nooks, crannies, and irregular areas of wall space quite well. It is also considered by many to be a “green” material, as it is composed of up to 75 percent recycled newsprint and does not contain formaldehyde, which can release harmful vapors into the air.

Another bonus is the fact that cellulose insulation can be added to walls by the ambitious do-it-yourselfer. Equipment for the job can be rented at many home improvement centers. Always wear safety goggles and a mask or respirator when working with this material.

1Use a stud finder to locate studs in the wall. With a hole saw, cut a small hole (between 2 and 3 inches wide) between two studs and near the top of the wall, and place the cut portion aside—you will reattach this later. Repeat this step between each pair of studs.

2Thread the blower hose into the first hole, and point the nozzle down deep into the wall cavity. Wrap a rag around the hose where it meets the wall to form a seal.

3While you hold onto the hose, have a friend turn on the blower. Pull the hose back as the cavity fills. Ask your helper to stop the machine when you feel resistance and can no longer insert insulation.

4Repeat steps 2 and 3, filling up the remaining wall cavities.


5Once you have finished, reinsert the drywall cutouts and patch up and paint over the holes.

Insulating with Cementitious Foam

While blown-in insulation has long been a favored method of filling the gaps in existing structures, new cementitious foam goes the extra mile by providing a fire-resistant, non-toxic barrier with improved insulating properties.

Cementitious foam is made entirely of magnesium oxide and air. It is blown through a membrane with air, resulting in a continuous network of mineral surrounding bubbles of air.

While it will require a professional to actually blow the insulation in, you can help reduce the time and cost of set-up by helping prep the area that needs insulation.

The insulation is thick enough to be retained by almost any netting, screening, or chicken wire, or it can be foamed in behind house wrap or polyethylene.

There are two things to pay attention to when prepping the area and hanging the membrane that will contain the insulation.

First, the membrane must be installed tightly against the wall studs to avoid “pillowing,” which can create an uneven surface and complicate drywall attachment. To avoid this, try stretching the netting very tightly or applying a coat of glue through the netting to secure it continuously to studs. If you are using polyethylene as a containment membrane, try stretching it hand tight and applying frequent inset stapling.

The second issue is that a vent will be needed to allow air to escape ahead of the filling insulation. If you are using chicken wire or netting, this isn’t a concern, but in airtight membranes you will want to slit a small vent to allow air to flow out of the filling space. Once the insulation is installed, you can seal the air vent.

Featured Resource: Find a Pre-Screened Local Blown-in Insulation Pro

About Don Vandervort
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Don Vandervort developed his expertise more than 30 years ago as Building Editor for both Sunset Books and Home Magazine. He has written more than 30 home improvement books and countless magazine articles. He appeared regularly on HGTV’s “The Fix,” and served as MSN’s home expert. Don founded HomeTips in 1996.

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