Photo: Kha Ruxury

Does vapor barrier go before or after insulation?

After the insulation is in place you will want to add a vapor retarder, sometimes called a vapor barrier, if you need one. Not every wall does. A vapor retarder is a material used to prevent water vapor from diffusing into the wall, ceiling or floor during the cold winter.

certainteed.com - Do I Need a Vapor Barrier? - CertainTeed

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You're building a wall. Maybe you're putting on an addition or finishing off your basement or maybe you are just about to undergo a major renovation that requires taking the existing wall down to the studs. Whatever your reason you are now looking at finishing a new wall. Whether you are doing it yourself or hiring a contractor it is a helpful to know a little about proper construction. Your first job after the studs are in place is to fill those walls with insulation. If you are not sure if you need insulation in your walls follow along with this flow chart. After the insulation is in place you will want to add a vapor retarder, sometimes called a vapor barrier, if you need one. Not every wall does. A vapor retarder is a material used to prevent water vapor from diffusing into the wall, ceiling or floor during the cold winter. 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. To know if you need a vapor retarder, ask yourself a few basic questions:

Map: Insulation Institute

What is my climate? If you live in a mixed climate – hot and humid with several heating months in the winter, you probably need a vapor retarder. Specifically, if you live in climate zones 4C (marine), 5, 6, 7 and 8. Not sure your climate zone? You can check here. What is my cladding type? According to the U.S. Census Bureau 2009 statistics, more than half of all new homes are clad with absorptive materials such as brick, stucco, wood, fiber cement or stone. These moisture-retaining claddings can worsen moisture challenges in the wall cavity. They have the potential to release moisture into the structure, creating an inward vapor that doesn't exist with vinyl siding. Where is the wall located? If you are adding an exterior wall, anywhere in the house, and you answered yes, to either of the above questions you should consider using a vapor retarder.

Vapor Retarder Use and Placement

In certain climates vapor retarders can be a vital part of the wall construction. However incorrect use can lead to additional moisture problems. Consult an insulation professional in your area if you are unsure where or how to install a vapor retarder or consider a vapor retarder that provides some degree of additional flexibility, like a smart vapor retarder. A smart vapor retarder is able to adapt its permeability to allow the wall to dry should moisture get trapped in the wall cavity. A smart vapor retarder is a vapor retarder material with the unique ability to react to changes in relative humidity by altering its physical structure. This material adapts to let moisture out of the wall whether the humidity levels are higher on the outside of the wall (winter) or the inside (summer). A smart vapor retarder is a good solution for areas of mixed climate. Wall construction is important to creating a healthy, comfortable home. Read more about vapor retarders and learn how they can affect the health of your home.