Is it OK to put plastic over faced insulation?

Asked By: Caroyln Zelinsk | Last Updated: 5th June, 2020
Category: home and garden indoor environmental quality
4.2/5 (5,249 Views . 20 Votes)
While we hear a lot about dual vapor barriers and the 5 to 1 rule, installing plastic sheets directly over faced insulation does not cause a moisture problem if installed correctly. The reason for this has to do with Relative Humidity (RH%) and the fact that moisture flow during the winter is pressure induced.

Click to see full answer


Also, can you put plastic over faced insulation?

In simple terms, a vapor barrier is a material that won't allow moisture to pass through it, such as plastic sheeting. It's designed to stop the moisture before it can enter the wall cavities. There are two basic types of vapor barriers used with exterior wall insulation. The most common is paper-faced insulation.

Also, does faced insulation need to be covered? To satisfy building codes, most faced insulation must be covered with half-inch-thick wallboard or other code-approved material to reduce the chances of its igniting during a fire. There is a type of faced insulation approved for exposed installations.

In this regard, should I put plastic over insulation before drywall?

Back years ago, it was always said to NOT put a plastic vapor barrier over the insulation before hanging drywall or whatever material you decide to hang, as it would cause the room or building to act like a greenhouse.

Do you need a vapor barrier with Kraft faced insulation?

In climates requiring a vapor retarder on the interior surface, a kraft-faced insulation is usually sufficient. When a loose-fill product such as fiberglass or cellulose is installed, a 4 mil continuous polyethylene sheet or a vapor retarder paint on the interior drywall should be used .

38 Related Question Answers Found

Do you put plastic behind drywall?

A continuous plastic vapor barrier behind the drywall will protect the interior walls of these areas from water damage.

Where should vapor barrier be installed?

Vapor barriers are usually best installed on the side of the wall that experiences the hotter temperature and moister conditions: the inner surface in colder climates and the outer surface in hot, humid climates. In existing spaces, oil-based paints or vapor-barrier latex paints offer an effective moisture barrier.

Does the paper on insulation go in or out?

Hi Kim, Regardless of whether fiberglass insulation is installed in a wall, attic, or crawlspace; the paper facing should always face toward the inside of the home. That's because the paper contains a layer of asphalt adhesive which prevents water vapor from passing through it.

Can you staple vapor barrier?


Installing Vapor Barrier on Stud Walls
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.

Do bathroom walls need vapor barrier?

It is important to make sure that a proper vapor barrier (or vapor retarder) is installed on the walls in your bathroom whenever you're building or remodeling. You don't need to put a vapor barrier in the ceiling of the bathroom.

Do you put a vapor barrier on the ceiling?

Plastic vapor barriers should only be installed in vented attics in climates with more than 8,000 heating degree days. Omitting a ceiling vapor barrier by arguing that "you have to let the moisture escape" or "because the house has to breathe out the top" is actually correct, in a way. It's also incorrect, in a way.

Should you insulate rafters?

Insulating between rafters will do no good, because the attic should be ventilated, and the rafter insulation would be between two unheated spaces. You can add insulation to the floor; the more the merrier. Also, make sure the attic is well ventilated. Cold roofs prevent ice dams.

Does Tyvek cause mold?

Building paper tears easier than DuPont Tyvek and can degrade over time when under continual exposure to water. Building papers are less permeable to moisture vapor transfer than Tyvek increasing the potential moisture vapor trapped inside the wall could cause mold, mildew and rot.

Do you need vapor barrier on interior walls?


Installing a vapor barrier on the (warm) interior wall of your cement brick house will prevent condensation and reduce air leakage through your walls and insulation. Because no vapor barrier can be perfect, and some water may still get in, you must create a venting path for the water to get through the insulation.

Can you over insulate a house?

Homes need insulation, and more is generally a good thing. But there may be a theoretical point of “too much.” If a home is over-insulated and is too tightly sealed, moisture can get trapped inside. This is not to say that if you have mold in your home, too much insulation is the culprit.

Do I need a vapor barrier?

In many colder North American climates, vapour barriers are a required part of building construction. You may find that vapour barriers are often not required in warmer climates. And, if installed in the wrong climate or on the wrong side of building materials, a vapour barrier can cause more harm than good.

Is Tyvek a vapor barrier?

No, DuPont Tyvek® is not a vapor barrier. It is made with unique material science to keep air and bulk water out while allowing moisture vapor inside walls to escape.

Does a vapor barrier prevent mold?

The original reason for using vapor barriers was a good one: to prevent wall and ceiling assemblies from getting wet. This can lead to significant moisture problems and mold; problems occur when walls get wet during construction or more often throughout the home's life.

Do I need vapor barrier in unheated garage?


Re: Use vapor barrier when insulating unheated garage? If it is an attached garage and we are talking about the wall between the garage and the living space then no, you do not need a vapor barrier. The house side of the wall will be warmer than the garage and any vapor will stay in the garage.

Where should faced insulation be used?

Faced, or the type with paper, is typically used in first-time applications, such as in walls, ceilings, floors, and in crawl spaces. Any time you use a faced insulation, the paper needs to be facing toward the living space. So in an attic the paper faces downward and in a crawl space, it faces upward.

Can you put a vapor barrier over faced insulation?

The special paper lining one side of the insulation is sufficient to block moisture and air. Some builders choose to attach a separate vapor barrier even with faced insulation, however. It doesn't hurt anything. The result, when finished, is a super-insulated wall with a foam vapor barrier instead of sheet plastic.