Do You Need A Vapor Barrier Under Attic Insulation

What you need is an air barrier that is at every step of the way you have to pay attention to airtightness.

Do you need a vapor barrier under attic insulation.

Adding a second vapor barrier could cause condensation to become trapped in the insulation between the two vapor barriers. With spray foam unlike with loose fill or batts you must cover the soffit vents they aren t needed to keep the roof cool. 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. Seal the air leakage pathways.

If you need a vapor barrier and your insulation is unfaced you must cover it with a polyethylene film. This acts as a barrier to keep heated moist air from rising up into the attic during cold weather. Lucy no you don t need a vapor barrier. 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.

Your first job after the studs are in place is to fill those walls with 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. If you are not sure if you need insulation in your walls follow along with this flow chart. No you don t need a vapor retarder class i or otherwise.

Then cover the foam with drywall as required for fire safety. Not every wall does. Air sealing an attic. In cold climates a vapor barrier is almost always needed.

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 are sheets of plastic or other material placed on one side of insulation sheets. In mixed climate areas the vapor barrier is optional depending on the total design of a building. The facing on faced insulation acts as a vapor retarder.

Plastic vapor barriers should only be installed in vented attics in climates with more than 8 000 heating degree days. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. The basics of air sealing are covered in this article. However all attics vented or unvented and in all climates should have an air barrier such as an airtight drywall ceiling.

In hot dry climates your attic can be vented though like in hot humid climates you should not install any vapor retarder or barrier. 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.