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How to Insulate Existing Walls

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.

The job of insulating existing exterior walls involves removing some siding panels so large holes can be drilled through the sheathing at the top of wall stud cavities. Then using 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.)

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.

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.

Here is a helpful video that shows the entire process of blowing-in fiberglass insulation, including methods for calculating how much you will need. Following this, you’ll find a step-by-step guide.


Blowing-In Insulation, Step-by-Step

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 & Saving Energy

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