Vapor Barrier On Concrete Basement Walls

Not to be confused with a vapor barrier which is placed on the warm side of the wall just in front of the insulation and behind the drywall a moisture barrier goes against the basement wall and.

Vapor barrier on concrete basement walls.

Usually that is right behind the drywall. The vapor barrier is sealed to the concrete wall at the bottom with some sort of seal and nailed directly to the concrete. The construction of the wall for instance is vital to the use of a vapor barrier. When the mold grows it will spread to everything around it studs drywall etc.

The water vapor can come through the concrete from the soil or from indoor air that comes in contact with the concrete. With fiber insulation and a vapor barrier moisture can get trapped in the insulation leading to moldy insulation and decay in the wood framing. Basement insulation vapor barriers the trick with basement insulation jobs is in understanding where water vapor is being stored and where it s moving to. If you have a framed wall that is adjacent to a concrete foundation wall where the vapor barrier is next to the drywall in front of the studs the fiberglass insulation gets wet and becomes a breeding ground for mold.

Vapor barriers are used because while fresh concrete is poured wet it s not supposed to stay that way. You should then use fiberglass insulation that has a vapor barrier between the studs with the vapor barrier facing in toward the living space. Building codes usually require a vapor barrier 4 mil plastic sheeting on exterior basement walls if the framing is attached to masonry or concrete surfaces or if the wood framing butts up against the outer basement walls. So there is enough gap for air to flow.

As the wall dries the water vapor leaves the concrete and tries to penetrate the insulation and wall. Hence it must always be located on the warm in winter side of any insulation. That is if the studs are going to touch the concrete wall. Of foam against the wall this should not be a problem in your climate.

Concrete is like a huge sponge which holds water and water vapor for years and years. Or you can leave a 4 inch gap between the studs and concrete wall and probably get away with it. It is designed to stop moisture in the form of vapour that is inside the house from moving into the walls and forming condensation or ice. The insulation and barrier extend right up into the joists where they are heavy duty stapled to the joists and flooring on the main level.

The vapour barrier is more properly called a vapour retarder.