Insulation in house exterior walls is one of the primary defenses against heat and energy loss. Unfortunately, however, builders didn’t insulate the walls of most homes built before the 1980s. So if your house was built before insulating walls became standard, you can potentially save a great deal of energy by insulating. But how do you get insulation into existing walls without opening them up? That’s what we’ll discuss here.

If you’re not sure whether or not your home is insulated, please see the article Inspecting Home Insulation.

You can insulate existing exterior walls either from inside or outside the house. When doing it from outside, the job involves removing some siding panels so that large holes can be bored through the sheathing at the top of wall stud cavities.

Then installers use special equipment to blow fiberglass fibers or cellulose insulation through the holes into the cavities. (If you’re not familiar with terms such as “sheathing” and “wall studs,” please see House Framing Diagrams & Methods.) Then the walls are plugged up and the siding is replaced.

Blowing insulation into walls from inside the house basically involves the same procedures but, instead of removing siding, holes are cut through the drywall with a large hole saw. Of course, this creates a serious mess indoors and requires extensive patching and painting of drywall. The following video gives you a pretty clear view of the mess and patching required.


Equipment for the job can be rented at many home improvement centers. In fact, some provide the equipment free if you buy about 20 bags of insulation. Always wear safety goggles and a mask or respirator when working with this material.

Shredded fiberglass and cellulose can be blown-in because their small particles fill in the nooks, crannies, and irregular areas of wall space quite well.


Blowing-In Insulation, Step-by-Step

1 Use 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.

2 Thread 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.

3 While 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.

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

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

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About Don Vandervort
Don Vandervort has developed his expertise for more than 30 years as a remodeler and builder, Building Editor for Sunset Books, Senior Editor at Home Magazine, author of more than 30 home improvement books, and writer of countless magazine articles. He appeared for 3 seasons on HGTV’s “The Fix,” and served as MSN’s home expert for several years. Don founded HomeTips in 1996. Read more about Don Vandervort