A person installing pink insulation into the wall of a house.

4 Steps to Installing Insulation

How to Install Insulation

Insulation is the stuff a fit-as-a-fiddle house is made of, an unsung hero behind the walls making a home a comfortable temperature, energy-efficient, and shielded from the noisy outdoors. Not all of us are hashtag-blessed with insulated homes, and sometimes, when doing house projects, we find crumpled-up newspapers in the walls that once served as a last-ditch effort to warm the house back in the day. This is why we are going to talk about how to install insulation.

If you are a long-time sufferer of inexplicably freezing cold rooms, gusty drafts, thundering outdoor traffic, and costly energy bills from cranking up the heat or air, then it’s time to insulate. Here’s how to install insulation yourself!

Let Insulation Work for You

Maybe you are avoiding this project because it seems daunting, or you remember how as a kid, your parents warned you never to touch insulation because it is filled with glass. With the proper safety gear and tools, anyone can do it, and here is what insulation can do for you:

  • Save on your utility bills: According to Energy Star, you could save between 5% to 16% on your entire home’s estimated annual utility bills by properly insulating and sealing.
  • Quieter: Adding insulation will absorb sounds, and sound-control insulation in your interior walls will help muffle noisy appliances.
  • Moisture control: Everyday chores like cooking, washing, or bathing produces steam. That water vapor can become trapped in the walls, spurring mildew and mold growth. Insulation acts as a barrier, protecting your home, your health, and curbing moisture.
  • Comfort: It’s true — insulation makes your home cooler in the hot summer months and warmer in the frigid winter months. Say goodbye, too-hot-or-too-cold closet.

Choosing the Right Insulation

Naturally, there is more than one type of insulation, but most importantly, you should know about the R-value.

All About That R-Value

The higher the R-value, the more effective the insulation is, based on its thickness and density. You can find what R-value you need in your insulation by looking at an R-value map of the United States. The U.S. is divided and color-coded into zones. When you determine the R-value for your location, check an online chart to see the recommended R-value for your project. Wall insulation will usually need a lower R-value than floors or crawl spaces.

Types of Insulation

  • Blanket (available in batts or rolls): The glass fibers entwined with fluffy sheets are great for unobstructed areas like attic joists. They will stop heat loss when placed in an attic or the walls. Be sure to measure and cut to fit your space. Batting should not be flattened or compressed as it’ll reduce the R-value.
  • Rigid foam: These are sheets of polystyrene used for joist placements or basement crawl spaces. If you use rigid foam, seal the space between its panels and the foundation joists with spray foam.
  • Reflective system: You’ll see this type available in foiled craft paper, plastic film, or cardboard material. It fits well with unfinished walls, ceilings, and floors.
  • Blown-in: Loose fiberglass insulation is directly blown into awkward spaces, gaps, and cavities. Blown-in insulation is used when a roll or batting does not make sense or is too difficult to apply. You can rent a blower unit or have a contractor do this for you.
  • Spray foam: This easy-to-use insulation expands as it cures, making it ideal for small, narrow spaces around piping, wire openings, or surrounding windows.

Installing Insulation

Fiberglass batts are the go-to style of insulation because they are the most cost-effective and easiest to install. Once you have landed on the R-value and insulation type, it is time to get to work.

You’ll need:

  • Safety gear: gloves, long sleeves, pants, safety glasses, and a proper mask
  • A straightedge
  • Utility knife
  • Caulking gun and caulking
  • Staple gun
  • Insulation (you can use an insulation calculator to determine how much you’ll need)

Step One: Trim the Width

The key to installing insulation correctly is to fill the stud cavity without leaving any gaps.

  • Trim the width of the batt insulation to fit the voids between studs. You’ll do this by laying the batt on the floor in front of the stud bay, lining up the edges to get an idea of the proper width you’ll need.
  • Use a straightedge (or some recommend a 2x4) to help guide your utility knife when trimming down the batt’s width to fit between the studs.

Step Two: Trim the Length

  • Fit the insulation snugly into the stud bay so the edges are flush alongside the studs. Avoid flattening and compressing the insulation because it will reduce its R-value.
  • Allow the insulation to trail past the bottom of the stud cavity so you can see how much to trim off for a perfect fit. Use your utility knife to trim the insulation so that it butts against the bottom of the wall framing.

Step Three: Awkward Spaces

There’s no doubt you’ll run into spaces that need insulation and aren’t the nice, neat bays you’re used to.

  • Wires: Split the thickness of the batt insulation in half, then sandwich the wiring between either side for optimal insulating.
  • Pipes: Work around any plumbing pipes by squeezing the insulation behind them to prevent freezing in the winter.
  • Outlet boxes: Work around any electrical outlet boxes by cutting a notch, using the box as an outline, and fitting the insulation around it.
  • Windows and doors: If you can, fit skinny strips of batting into drafty spaces around windows or doors (without packing it). Grab a can of expanding foam to fill in the gaps.

Step Four: The Vapor Barrier

Most batting is faced with paper or foil with a retarder built-in, but you can install one yourself if that’s not the case.

  • Grab 6-millimeter plastic to make a breathable protective layer.
  • Secure the plastic every 12-24 inches on the top plate, the studs themselves, and the bottom plate.

When to Call the Pros

While insulating a room can be easy, it may be better to have a professional contractor do it if you have many rooms to insulate or are faced with hard-to-insulate spaces. Blown-in insulation is best left to the professionals, but for run-of-the-mill fiberglass batting, you can tackle an average-sized room in about five hours or less.

Insulation is also a cheap project that will save you even more money down the road. Expect to pay about 79 cents per square foot for basic insulation. Hiring a professional will, of course, cost more, but if you have a big insulation project, ask yourself, how much is your time worth?