In cold climates the opposite is true. Vapor barriers are used because while fresh concrete is poured wet its not supposed to stay that way. Nor do you want poly between gypsum drywall and the insulation.
Not every wall does.
Basement vapor barrier or not. Building vapor barriers are generally considered beneficial necessary and required for building code compliance so i realize that taking a poke at the status quo will lead to some hostility. This is asking for trouble especially with a full bathroom which generates a lot of humid air. If you are not sure if you need insulation in your walls follow along with this flow chart. Vapor barriers are only used with insulation.
Avoid foam insulation that is faced with. In most cases these basement walls were insulated with fiberglass batts and included two. Or you might consider spray foam between the studs. The short answer is.
A concrete vapor barrier is any material that prevents moisture from entering a concrete slab. Mold when basement vapor barriers are bad vapor barriers can be misguided when used as dictated by building codes in cement basement walls. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. Should i include a polyethylene vapor barrier.
The placement of the vapor barrier depends largely on the climate where your house is. The purpose of it is to reduce and slow down the transmittance of water vapor to prevent condensation. Rigid foam board on the interior like you have is the ideal insulation. Of foam against the concrete.
After reading your website i realized that this approach isnt the best. You dont want poly between the concrete and the insulation. Dont use a vapor barrier in a finished basement. I originally had planned to put a 3 mil vapor barrier directly against the basement walls painted concrete and then frame while leaving a gap between the frame and basement wall and insulate with fiberglass batts.
You dont want poly anywhere. It needs to dry and then stay dryto avoid flooring problems. Unfaced fiberglass or roxul rock wool is also acceptable if you already have 2 in. Vapor barriers are not actually barriers at all but vapor diffusion retardants or vdrs which at the molecular level balance the flow of moisture.
After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. Remove the vapor barrier against the basement wall. The rationale was the 3 mil vapor barrier would serve to protect the framing from any water intrusion ie such as the vapor given off from the walls as in your first figure. Basement wall systems should never include any polyethylene.
The word barrier has the inference of a solid seal that would stop any moisture flow but these or any materials would let some vapor pass through. In warm climates the barrier should point to the outside of the house blocking the vapor from the humid outside air that may seep into the walls or ceilings. Paul ellringer an energy and mold consultant in saint paul minnesota has a collection of slides showing moldy basement insulation. All heat has moisture in it and insulation slows down heat flow but does not slow down the water vapor flow.
