My questions is in regards to adding a vapor diffusion retarder especially with the slap on grade.
If using vinyl, or some other heavy mill plastic lying on the ground obviously separating the ground from the underside of the decking, wouldn’t that be a cause of concern where any kind of moisture buildup laying on top of the retarded material could like to still water buildup which could draw mosquitos, grow mold etc…?
Wrong term in this case. Think permeability.
Class I vapor retarders (0.1 perms or less):
Class II vapor retarders (greater than 0.1 perms and less than or equal to 1.0 perms):
Class III vapor retarders (greater than 1.0 perms and less than or equal to 10 perms):
Vapor retarders can help control moisture in:
A vapour barrier is a plastic membrane laid under the slab to improve its performance against rising damp. It is also called a ‘moisture barrier’ because it stops the moisture from the soil migrating into the concrete slab.
So to add some more insight, my son in Idaho recently bought a house and when the inspector came to his house, he looked at the crawl space under his house as he has no basement. The inspector noted that by code and properly installed was a thick polymil barrier separating the ground from the crawl space framing.
Moisture is going to collect on top of that, it has to, which leads to my question about stagnant water laying on top of the polymil.