Vapor Barrier Under Concrete Slab On Grade

A concrete vapor barrier is simply a sheet of polyethylene plastic visqueen placed directly on top of the sub grade before the concrete floor or slab is poured to help keep moisture from the soil from passing up through the concrete.

Vapor barrier under concrete slab on grade. I have a home that i did a substantial renovation on 3 years ago. We would like to resolve the question of proper placement of vapor barriers under concrete slabs on grade. A vapor barrier is any material with a. Vapor barriers for slabs on grade.

Vapor retarders are materials that will minimize the transmission of water vapor from the sub slab support system into a concrete slab. Vapor retarders have been used since the 1950s. Vapor barriers under concrete floor slabs. Vapor retarders are typically specified according to astm e 1745 and have a permeance of less than 0 3 us perms 0 2 metric perms when tested by astm e 96.

By steve ragan director research and technical services the answer to this controversial question from both angles is a qualified yes vapor barriers have been associated with certain concrete slab on grade problems including curling and cracking. Concrete vapor barriers ers under slab vapor barriers done right concrete vapor barrier what is a vapor ers necessary for bats vapor barrier under concrete slab vapor ers under slabs on grade. Pouring a slab on grade is a common way to lay a sturdy floor or foundation where a basement or crawlspace is unnecessary. We have a system that has worked well for us in the past.

That s why in most cases a vapor barrier should be installed under the slab. However the far greater risk to a slab is long term curling over the lifetime of the concrete foundation which a high performance vapor barrier helps prevent. Recently though research has shown that the old traditional layer of 6 mil visqueen polyethylene plastic under the slab is seldom effective for two main reasons. In nonproblem areas we have traditionally used 6 mil polyethylene film directly under concrete slabs and over a granular fill on the subgrade.

Without a vapor barrier moisture would continually wet the bottom of the slab as vapor will continuously drive from the high humidity below slab to the relatively low humidity above. The best way to accomplish that is with a vapor barrier under the slab. In various places around the house we installed a gypcrete leveling course 1 2 5 8 and then a glued down engineered wood.