Installing Vapor Barrier in a Basement

Why Use a Vapor Barrier

There are many schools of thought on the effectiveness of a vapor barrier, also referred to as a vapor retarder. This protective sheet is secured to basement walls to stop moisture generated within the home from seeping into the walls. If moisture affects the walls, it may result in a serious problem with rot, mold, and mildew.

Here are other times when moisture problems can occur:

• The barrier is not positioned correctly, torn, or installed loosely around outlets, pipes, and other connecting areas.
• Insulation with a vapor barrier facing is installed with the barrier facing the room, rather than the wall.
• Supplemental insulation with an attached vapor barrier is layered over existing insulation.

Any of these circumstances will render a vapor barrier useless.

Vapor retarders are made from the following materials:

• Paper-backed aluminum
• Paper-backed insulation, also referred to as a Kraft paper facing
• Polyethelene plastic sheet, known as Visquine
• Roofing membrane sheets
• Rigid insulation

Do You Need One Where you Live?

The confusion over installing vapor barrier in a basement stems from whether your home actually needs it, and if so, in which direction must the barrier face in order to prevent moisture.

In fact, not all homes do need this application.

Here’s a simple rule of thumb to guide you:

• If it’s cold where you live more than half the year, install vapor protection on the inside, with the barrier facing the warm side, or interior, of the wall. This keeps moisture from reaching the outside walls and forming condensation.
• If it’s hot and humid where you live, install vapor protection on the outside, with the barrier facing the warm side, or exterior, of the siding or wood. This prevents moisture from penetrating the inside walls.

If you have an even mix of seasons, you might not need a vapor retarder at all. Review the local building codes in your area to find out what the professionals recommend.

Note that if you’re pouring a concrete basement floor, you’ll need a vapor barrier, regardless of where you live. A cross-laminated polyethylene sheet works in most situations. Check with your local hardware store for more direction.

Tips for Installing Vapor Barrier in a Basement

• Check all walls for damage, including cracks and existing moisture. These must be repaired before adding a barrier.
• Building experts recommend installing vapor barrier in a basement against the foundation walls before placing studs and insulation.
• If the studs are already in place, staple the material to the studs. Pull it tightly across, and cover large surfaces as flatly as possible.
• Make sure not to tear or cut the material.
• Align the barrier right up to electrical outlets, pipes, windows and other obstructions, and use a sealant to secure the material.
• Install non-faced insulation over the vapor barrier. If your insulation has a barrier already attached, or you're installing new insulation over old, make long cuts into it so that you don’t create a bubble effect. Moisture could seep in between the barriers, rotting the insulation.
• With that said, you don’t need to install a vapor retardant if your insulation has that protection attached. But remember--the paper barrier side faces the interior, or heated, wall, and the insulation side faces the exterior.
• Don't manipulate the insulation in any way. It does not have to be fluffed, puffed, or stretched, and doing so could tear any attached barrier. Just unroll it and put it up.
• Some forms of rigid insulation serve well as vapor barriers. Check the coding to see if your selection pulls double-duty.

Depending on the size of the basement, the job should take two people about four hours. Material costs will vary based on square footage and type of material used. Check the building codes in your area to make sure you don’t need a permit.

Also, take the necessary precautions when handling insulation. Wear a face mask, eye protection, work gloves, and long sleeves.