Does Blown In Fiberglass Insulation Need A Vapor Barrier

Chopped pink fiberglass insulation poured or blown into an attic in a somewhat sloppy uneven installation.

Does blown in fiberglass insulation need a vapor barrier.

Carl whitis belen nm above. The insulation keeps the sheathing warm enough to prevent condensation of the water vapor. But if the paper looks the same on both sides then there isn t a vapor retarder and a different material may be installed over it. Whether or not you need a vapor retarder hinges on three main factors your climate your home and the location of the wall you re insulating.

After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. Vapor barriers applied over the face of the insulation provide additional benefits in the fight against moisture. A common misconception is that all insulations require vapor barriers in all situations. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter.

In a vented attic no vapor retarder is necessary but with the ducts air handler in the attic it might make more sense albeit much more expensive to insulate at the roof deck with a combination of spf and fiber and insulate seal the gable ends. Research has shown that this is incorrect. In your area i would definitely install one of the two. There might always be water vapor in the insulation but it cannot condense because the sheathing is warm.

There are three types of blown in insulation. By chris moore fiberglass insulation must stay dry to be effective. In most climates it needs a vapor barrier. Like other batt type insulation fiberglass has a predictable r value if not compressed but is difficult to fit around obstacles without leaving gaps.

Fiberglass batts the insulation found in most houses in the u s are inexpensive and quick to install. If the paper is coated with asphalt on the side next to the fiberglass than that is the vapor retarder and no other barrier should be installed over it. This barrier is meant to keep moisture from getting to the insulation in the walls and ceilings and it is required by building codes when insulating most houses. But it ll be at least a 5x cost multiplier unless most of it is diy.

Cima does not recommend the use of vapor barriers with cellulose insulation except in circumstances of exceptionally high moisture levels such as an indoor pool facility or very cold climates. Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets. Fiberglass insulation cannot fight the battle against moisture intrusion alone however. The three most common types of blown in insulation are loose fill fiberglass cellulose and rock wool each with its own pros and cons.