Attic Insulation: How to Install a Vapor Barrier

A tin-foil background.
  • 24-72 hours
  • Intermediate
  • 100-200
What You'll Need
Foil or plastic sheeting
Putty knife
Staple gun and staples
Duct tape
Board for kneeling on
Tape measure
Dustpan and brush

Most forms of attic insulation benefit from the addition of a vapor barrier to protect them from the harmful effects of moisture, which can reduce their effectiveness over time. The following are a few simple steps to help you undertake the task properly so your vapor barrier retains heat without damaging the insulation.

Step 1—Prepare

Begin the process of fitting a vapor barrier for attic insulation by preparing the space for the job. Remove any transferable items from the attic so that they do not get in the way as you work. If there is limited lighting, find a way to provide more so you can see what you're doing.

Clean the entire attic with a dust pan and brush or vacuum cleaner, either way ensuring that you get into all the corners and crevices. Fill any cracks or holes you find to reduce the amount of heat that can escape through these means. Take a note of the construction of the attic and figure out which type of barrier will be suitable.

Step 2—Measure

To install an efficient vapor barrier, you need the dimensions of the room. Measure the entire area and write down the results. Do not overlook attic access door. Take the measurements with you when purchasing materials.

Step 3—Install Insulation

Many types of blanket attic insulation already have a vapor barrier incorporated into them and will be effective at reducing moisture problems if fitted correctly. Make sure that you read the instructions carefully so you know which side is the vapor barrier and how to install it. Blanket-style insulation often comes in a roll, which can be cut to fit between joists before being tucked into the sides. Secure the roll at one end and then unfurl it, continuing to tuck it in until it is firmly in place. Don't forget to wear protective clothing while doing so.

Step 4—Install Vapor Barrier

For loose-fill and blanket insulation that does not come with a vapor barrier, buy a vapor barrier separately. It usually comes in rolls, which make it easy to fit in place. Lay the first few inches of the barrier sheet to the base of the wall and press it into the corner. Staple it into place.

If you are reluctant to use staples, secure the barrier with duct tape instead. Gradually roll the barrier out and use your chosen method to secure it at regular intervals. As you work, sweep your hand across the surface to push out air and keep the barrier flat. Cut the vapor barrier when you reach the end of the room, making sure you leave enough excess to form an edging lip.