Do You Need A Vapor Barrier Under Attic Insulation

With spray foam unlike with loose fill or batts you must cover the soffit vents they aren t needed to keep the roof cool.

Do you need a vapor barrier under attic insulation. 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. You can forego the plastic and use a vapor retarder kraft faced insulation or latex ceiling paint in all other climates except hot humid or hot dry climates. In cold climates a vapor barrier is almost always needed. The basics of air sealing are covered in this article.

If you are not sure if you need insulation in your walls follow along with this flow chart. This acts as a barrier to keep heated moist air from rising up into the attic during cold weather. Your first job after the studs are in place is to fill those walls with insulation. Seal the air leakage pathways.

What you need is an air barrier that is at every step of the way you have to pay attention to airtightness. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. Adding a second vapor barrier could cause condensation to become trapped in the insulation between the two vapor barriers. However all attics vented or unvented and in all climates should have an air barrier such as an airtight drywall ceiling.

Not every wall does. The facing on faced insulation acts as a vapor retarder. Attic insulation should always be installed with the paper backing facing toward the living space the ceiling in this case. Foam blocks airflow needs no vapor barrier and has a higher r value per inch than loose fill or batts so you ll get more protection with less depth.

By the time you paint the drywall though you ve brought it into the class iii vapor retarder range between 1 and 10 perms and even less water vapor will diffuse through. If you need a vapor barrier and your insulation is unfaced you must cover it with a polyethylene film. In hot dry climates your attic can be vented though like in hot humid climates you should not install any vapor retarder or barrier. The best approach for a vented attic in a cold climate is installing a layer of drywall with a good coat of latex paint the paint creates a semi permeable vapor barrier.

No you don t need a vapor retarder class i or otherwise. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. Lucy no you don t need a vapor barrier. Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets.

Plastic vapor barriers should only be installed in vented attics in climates with more than 8 000 heating degree days. In mixed climate areas the vapor barrier is optional depending on the total design of a building.