What is the Best Vapor Barrier to Use Under Concrete Slabs? (2024)

FAQs

What is the Best Vapor Barrier to Use Under Concrete Slabs? ›

The American Concrete Institute (ACI) also recommends a minimum of 10 mil polyethylene or thicker for vapor retarders under concrete. According to its Guide to Concrete Floor and Slab Construction ACI 302.1R-15, thicker poly provides a better barrier and is also more puncture resistant.

The most commonly used vapor barrier under concrete slabs is polyethylene (poly) plastic sheeting with a thickness of 10 mil or 15 mil.

You should put gravel that is 3/4 to 1 inch under a concrete slab. However, depending on the project, local building codes may dictate the proper gravel size and shape. Some concrete slabs that do not hold significant weight may have a subbase of sand.

The American Concrete Institute's Guide for Concrete Floor and Slab Construction recommends that the thickness of the vapor retarder be at least 10 mils.

Under-Slab Moisture Barriers

The Guide to Concrete Floor and Slab Construction recommends a vapor retarder thickness of at least ten mils thick to resist puncturing during and after construction. (one mil equals one-thousandth of an inch).

What is the Best Vapor Barrier for a Crawl Space? The best way to stop the water and toxic gases in the ground from entering the crawl space and ultimately damaging your home or building involves installing a puncture-resistant, low-permeance Class 1 polyethylene vapor barrier with a thin poured concrete slab over it.

PERMINATOR TAPE is a self-adhesive tape, used in conjunction with the application of PERMINATOR underslab vapor barrier. PERMINATOR TAPE is for use in sealing vapor barrier seams and attachment to footings, protrusions, etc. Backing stabilized to resist the effects of UV exposure.

The most commonly used materials for a sub-base include gravel, crushed stone, and sand. Gravel: It's a popular choice due to its excellent drainage properties and ability to distribute the load evenly. Gravel also resists frost heaving in cold climates.

What is Vapor Barrier? A plastic sheet that is placed between the base and the concrete slab. Always placed beneath the rebar or wire mesh and on top of the gravel base. The sole purpose of the vapor barrier is to prevent moisture from penetrating through the concrete.

Sand can make an excellent base for paving slabs. It is very cost-effective and not too difficult for DIY beginners to work with.

What happens if there is no vapor barrier under a slab? ›

Even if the concrete foundation is enough to keep water away from the building, water vapor can easily rise to the surface and damage a building's foundation, subfloor, and main floor.

In general, place the concrete slab directly on top of the vapor barrier, with the subbase below. If the subbase is sharp angular gravel, a thin layer of sand can be placed on top of the gravel subbase next to the vapor barrier. See below for more discussion on this.

The 2021 International Residential Code (R408. 3) mandates covering exposed earth with a continuous Class 1 vapor barrier for unvented under-floor space. Additionally, the vapor barrier must overlap joints by 6 inches (152 mm) before sealing and taping.

The American Concrete Institute (ACI) also recommends a minimum of 10 mil polyethylene or thicker for vapor retarders under concrete. According to its Guide to Concrete Floor and Slab Construction ACI 302.1R-15, thicker poly provides a better barrier and is also more puncture resistant.

Flooring moisture barriers are placed beneath the floor's underlayment. You can buy a barrier separately or get underlayment with a moisture barrier built-in. If any water vapor penetrates through a concrete subfloor, the vapor diffusion retarder slows the movement of the moisture, preventing damage to the floor.

Generally, you'll want to use a low-permeance vapor barrier when protecting a slab that moisture-sensitive materials like adhesives and floor coverings will cover.

In general, place the concrete slab directly on top of the vapor barrier, with the subbase below. If the subbase is sharp angular gravel, a thin layer of sand can be placed on top of the gravel subbase next to the vapor barrier.

Install rigid foam panels across the foundation. To ensure maximum efficiency, make sure they lay flat. Lay foam around the perimeter of the foundation to level it with the concrete after it is poured. Leave a vapor barrier between the insulation and the gravel.