Vapor Barrier On Concrete Basement Walls

Vapor barriers are used because while fresh concrete is poured wet it s not supposed to stay that way.

Vapor barrier on concrete basement walls.

With fiber insulation and a vapor barrier moisture can get trapped in the insulation leading to moldy insulation and decay in the wood framing. 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. Most jurisdictions require a 4 mil plastic sheet vapor barrier for basement walls against concrete. It needs to dry and then stay dryto avoid flooring problems.

As the wall dries the water vapor leaves the concrete and tries to penetrate the insulation and wall. That is if the studs are going to touch the concrete wall. The water vapor can come through the concrete from the soil or from indoor air that comes in contact with the concrete. 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 ve ever had a problem with a basement floor or any concrete floor you know the kind of damage that too much moisture can cause. 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. 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.

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. 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. Hence it must always be located on the warm in winter side of any insulation. So there is enough gap for air to flow.

You should then use fiberglass insulation that has a vapor barrier between the studs with the vapor barrier facing in toward the living space. The vapour barrier is more properly called a vapour retarder. Or you can leave a 4 inch gap between the studs and concrete wall and probably get away with it. The construction of the wall for instance is vital to the use of a vapor barrier.

Of foam against the wall this should not be a problem in your climate.