How to Determine If Walls Are Insulated

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Project Overview
  • Working Time: 15 - 30 mins
  • Total Time: 30 mins
  • Skill Level: Intermediate
  • Estimated Cost: $5 to $50

If your house is too cold despite a smoothly running furnace or too hot despite fantastic air conditioning, you probably wonder what's going on. As long as you have effective windows, good weatherstripping, and attic insulation, your house should stay at a moderate temperature with the HVAC system running intermittently. The next logical thought might be: Do I even have insulation in the walls? Unless you bought the house new, built it yourself, or remodeled it yourself, it's not always easy to know the answer to this question.

Attic insulation, by contrast, is usually fairly easy to check. Simply find the attic access panel (usually located in a closet or hallway), set up a ladder, and pop your head into the attic. You will instantly know whether or not you have insulation. If you happen to have a walk-up attic with floorboards, it's usually easy enough to pry up a floorboard or two and check to see if the spaces between joists are filled with insulation. Checking the walls? Not so simple.

Common Methods Usually Don't Work

Two common methods do not yield definitive answers—touching the wall and knocking on the wall. One recommended method says that uninsulated walls will feel cold to the touch. But this is true only when there is a significant difference between interior and exterior temperatures. And to diagnose a wall, you need to have another insulated wall somewhere in the house with which to compare it.

Knocking on the wall is even less reliable. Conventional wisdom says that uninsulated walls will sound hollow. But unless you are highly experienced at this, insulated walls often sound just as hollow as uninsulated walls.

Methods That Do Work

Short of removing drywall to inspect the wall cavities, there are a number of steps you can take to check the walls for insulation. Some of these methods are invasive, but only slightly so. In some cases, you'll need to create small holes, but they are usually easy to cover or patch.

It's generally not necessary to go through all the following steps, nor will you need all the listed tools. When you reach a step that verifies whether or not your walls are filled with insulation, you can stop.

What You'll Need

Equipment / Tools

  • No-touch circuit tester
  • Screwdriver
  • Cordless drill
  • 3/4-inch hole saw
  • Flat pry bar
  • Brad gun or cordless nailer
  • Flashlight
  • Inspection scope
  • Stud finder
  • Hammer


  • Drywall patch kit
  • Wire coat hanger


  1. Inspect Through an Electrical Box

    Cutting a sizable hole in the drywall will certainly determine if you have insulation. Fortunately, your walls already have many holes in the form of the cutouts that hold electrical boxes for light switches and outlets.

    Determining whether you have insulation could be as easy as removing the cover plate on a switch or outlet, then looking into the gaps around the electrical box. Fiberglass batt insulation or loose-fill insulation will often be evident in the spaces around the electrical box.

    For a closer examination, you may be able to remove the electrical box entirely to look into the wall cavity. This method does not work for electrical boxes that are nailed to the studs, but old-work (remodel) boxes can be removed entirely since they are not nailed in place.

    Start by shutting off the circuit that powers the switch or outlet in the old-work electrical box. Check the outlet or switch box for power, using a no-touch circuit tester.

    Disconnect the device from the circuit wires, then remove the device. Now, extract the box from the wall. If necessary, you may need to detach the electrical cables from the box to do so. With a flashlight or wire probe, you can now examine the walls for insulation.

    When finished with the inspection, reattach the electrical cables to the box, insert it into the wall, and reattach the outlet or switch. Turn the power back on.

    Power Switch Construction
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  2. Check Behind the Baseboard

    During installation, drywall contractors sometimes leave a gap at the bottom of the drywall panels, which is then covered by the baseboard trim molding. These moldings are usually just nailed in place with brads or finish nails, and by prying a section of baseboard free, you can often determine if there is insulation in the walls.

    Carefully work a flat pry bar behind the molding, using a thin, flat piece of wood under the head of the tool to protect the wall. If your trim has a base shoe molding as well as a baseboard, remove the shoe molding first, then the baseboard.

    Examine for cracks between the bottom of the drywall panel and the edge of the wooden soleplate. Sometimes all you'll see is the soleplate, but if the drywall panel is elevated enough, you may see the kraft-paper facing of the batt insulation. Or, if your walls have loose-fill insulation or spray foam insulation, you may see traces of this in these gaps.

    If the drywall panels are tight against the floor, don't replace the baseboard just yet. The next step will show you another way to check for insulation.

  3. Cut a Hole in the Drywall Behind the Baseboard

    If insulation is not visible at the bottom of the drywall, you can cut a small hole about 2 inches above the floor. This hole must be just above the wooden soleplate, but still lower than the top of the baseboard. And the hole must be located in a space between studs.

    With the baseboard removed, use a stud finder to locate the wall studs. Mark a point on the wallboard in a space between studs, about 2 inches above the floor. Drill a hole through the drywall at this point. A small 3/4-inch hole saw is the best tool for this job

    Insulation that runs the entire length of the wall cavity will get caught in the hole saw. A reasonable conclusion is that the entire wall has insulation. If you see no insulation, you can extend an inspection scope into the wall cavity and look upward for insulation. You could also use a wire clothes hanger with the end bent into a hook to probe the wall. If the wall is insulated, the hook will probably snag fragments of insulation.


    Inspection scopes that attach to a smartphone are relatively inexpensive, or you can lease an inspection scope at a tool rental outlet.

    When your inspection is done, reinstall the baseboard molding. The hole you drilled should be entirely covered by the baseboard.

  4. Cut a Hole Above Kitchen Cabinets or in a Closet

    If removing a baseboard is not practical, another option is to cut a hole in the wall in a high area that is not visible. For example, a hole cut above a kitchen cabinet or above an upper closet shelf is not likely to be seen, even if it is never repaired.

    Locate a hidden spot above a cabinet or closet shelf, then use a stud finder to locate wall studs. As with other methods, you first want to locate studs so that you do not inadvertently drill into one of them. Mark a point on the wall between the studs, as low as possible on the wall.

    Cut a 3/4-inch diameter hole at this point. Use an inspection scope or wire to check inside the wall.


    Because blown-in insulation can settle and leave a space at the top, it is important to check the wall cavity several feet down. With the wire hanger method, you can probably hear the hanger tapping both ​sides of the wall. With the inspection scope, it is visually obvious.

    Small holes cut in these locations may not be visible at all, but if you choose they can be patched using a self-adhesive drywall patch kit, or with ordinary drywall joint tape and taping compound.

    A small 1/8 or 1/4 inch drill bit can be used to drill in between studs in an inconspicuous spot. Fiberglass insulation will generally start twisting onto the bit. Blown in insulation will generally leave a residue that can be detected on the bit. A bit of spackle and paint repairs the small hole.

    A home energy heat loss or gain analysis is usually the best method of determining if your home is properly insulated. It will usually require a company with the proper equipment to thermally scan the walls. Sometimes utility companies have a service for free or a minimal charge.

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