Fiberglass Insulation in the Attic 2 - Installation

Lead Image
  • 4-40 hours
  • Intermediate
  • 500-5,000
What You'll Need
Tape measure
Utility knife
Fiberglass batt insulation
Staple gun
Heavy-duty staples
6 mil polypropylene vapor barrier

Part one of this three-part series covered all the steps necessary before you can start installing your insulation. This installment covers the installation itself.

Step 1 - Prepare

Working on your knees in a hot attic for long periods of time can be very tiring. Plan to take a few breaks in your work time. Try to work early in the morning before it gets too hot. You will be covered from head to toe in clothing and gear. It may help to add a spray container of cold water to your tool box so you can spray yourself and your fogged up goggles.

Step 2 - Install Insulation

Man wearing mask installing insulation

Using a steel tape measure, measure the length of the space. When you know how long each piece needs to be, cut the fiberglass batting with a very sharp utility knife. Cut each piece an inch or two longer than needed to assure a snug fit. Use a straight edge to assure a good straight cut across the fiberglass batt.

Staple the batt to the rafters or scabbed-on boards with a staple gun so that the paper backing is toward the interior of the room to act as a vapor barrier. Use 3/8-inch, heavy-duty staples every six inches. Attach the insulation by the paper flange, so as not to compress the fiberglass. Make sure the paper flange and the staples are flat against the board to create an even surface for attaching the finished wall material.

Where the spacing of the rafters is uneven, at an odd angle, or not standard, you will need to cut the insulation to fit. Cut it one inch wider then the necessary width and tuck the fiberglass in to create a flange for stapling.

When installing insulation over wires, pipes, or fire blocking, back cut the batt to fit over the obstacle, leaving the paper intact and the insulation uncompressed.

Step 3 - Install Vapor Barrier

attic under construction

Once the insulation is in place between all of the rafters, staple up a vapor barrier of six mil polypropylene (a painter's drop cloth) along the face of the rafters. Although the paper or foil backing of the insulation is a vapor barrier, the added polypropylene covers completely. This assures no moisture will form in the cavity.

As you staple the vapor barrier to the rafters, draw it as airtight as possible, but be careful not to puncture the plastic unnecessarily as you put it in place. Should this occur, repair it with duct tape.

Extra Tip

Vinegar makes an effective rinse when you bathe or shower after working with fiberglass. It almost eliminates the itching that comes from the small particles of glass left on the skin. Once you're cleaned off, check out part 3!