How to Install a Vapor Barrier Over Fiberglass Insulation

a roll of Vapor Barrier
  • 3-5 hours
  • Beginner
  • 50-300
What You'll Need
Vapor barrier
Staple gun
Duct tape

Installing vapor barrier over your fiberglass insulation not only saves you money on your utilities, but it also keeps your basement dry and free of mold and mildew, which is detrimental to your family’s health. Because air is constantly heating and cooling, it is hard to control how much moisture enters your home. But it is a known fact that the more moisture enters your home, the more you will also find mold and mildew. Breathing in air saturated with mold promotes respiratory complications. One of the best ways to prevent this from happening is by installing a vapor barrier over your fiberglass insulation in the basement of your home.

Step 1. Special Notes About Vapor Barriers

It is important to note that insulation and vapor barrier are always installed facing the living space and never the other way around. This is because you want to keep the moisture out. First install the fiberglass insulation between the studs and then apply the vapor barrier over the installed fiberglass insulation. When installing your vapor barrier, it is important not to compress your fiberglass insulation, because they need to remain fluffy in order to keep its R-value.

Step 2. Installing Vapor Barrier Over Your Head

In most homes, finished basements and various floor levels have insulated ceilings; therefore, it is necessary to install vapor barrier on the ceilings to prevent moisture from traveling upward towards the next living level. To install the vapor barrier over the fiberglass insulation over your head, it is generally best to start at one end of the room and work your way across to the other end of the room stapling every six to eight inches along the outside frames and rafters. You should allow for overhang all the way around so that when you have finished installing that no draft is able to get through, effectively creating an air tight joint.

Step 3. Installing Vapor Barrier on Stud Walls

To install the vapor barrier on stud walls, it is generally best to start in one corner and work your way around the room allowing the vapor barrier to hang down from the top framing sill. When you have made it around the room, allow for approximately two stud section overlap in the corner where you started at. This is added protection for a tight seal.

When you have stapled the last of the hanging vapor barrier over the fiberglass insulation, it is then time to go back to the studs and begin to staple your way down to the floor sill on each one, allowing 6 to 8 inches between staples. Once you have repeated this process all the way around the room, it is then time to staple down the plastic vapor barrier to the floor sill.

Step 4. Taping the Seams of the Vapor Barrier

Once you have fastened the vapor barrier all the way around the room, including the ceiling, you need to go back to each seam and seal it tight using duct tape. This tape is sticky and creates an air tight seal for the vapor barrier. If you have torn the vapor barrier accidentally when stapling or by pulling on it, you also need to apply tape to these holes as well.