Crawl spaces beneath older houses are usually vented, meaning they have small openings to let air pass freely between the crawl space and outside. In practice, however, these vents don’t do a good job of circulating air, so whatever moisture makes it under the house will stay there. In humid climates, vented crawl spaces are especially damaging. Moisture-laden air enters the crawl space and condenses into water droplets on cool pipes and concrete walls, which promotes mold, fungus, mildew, and bacteria. Fortunately, vented crawl spaces can be sealed with the proper installation of a crawl space vapor barrier.
Contact our vapor barrier experts today at 760-388-6294.
Crawl space vapor barrier thicknesses range from 6 mil to 20 mil, with 6 mil being the bare minimum and 20 mil being the most heavy duty and puncture-resistant.
Why a Crawl Space Vapor Barrier?
Sealing off your crawl space can prevent rodents, bugs, or other pests from making their way into your home. Moisture creates a hospitable environment for undesirable guests, and if left unaddressed, moisture can destroy the subfloor of your home — and along with it, the foundation. Depending on the extent of the damage, the cost to clean and/or repair a crawl space can be considerably high, which is why the preventive measure of installing a vapor barrier is the preferred course of action.
Sealing an open crawl space with a vapor barrier can also prevent moisture accumulation in your floors and living space, saving your home from wood rot and mold. Plus, you’ll realize significant energy savings.
Crawl Space Vapor Barrier Materials
Reinforced polyethylene plastic sheeting (poly) comes in a variety of thicknesses and strengths. A 6 mil thick poly is commonly used as a vapor barrier and offers short-term savings to the homeowner. However, those savings may likely be lost in the long run if someone walks or crawls on the poly, causing micro holes in the vapor barrier. Once there are holes in the vapor barrier, however small, it will no longer function as a true vapor barrier. For this reason, depending on soil conditions, Americover recommends 10 mil and higher for long-term vapor protection.
Another concern is that polys stocked at local hardware stores are often thinner, non-reinforced, and could be made out of recycled or “regrind” poly. Regrind poly may contain impurities such as dirt or moisture. While thinner plastic or regrind may be okay for short-term use, only reinforced virgin poly should be used for long-term applications like crawl space vapor barriers. Properly installed virgin reinforced poly should last 20 years or more in a crawl space.
How is Vapor Barrier Thickness Measured?
There are two measurements you should be familiar with when choosing your poly for your crawl space vapor barrier. ‘Mils’ is the measurement of the poly’s thickness, and perms represent permeability to moisture.
- Mils: Polyethylene sheeting is measured in ‘mils.’ A mil is equal to 0.001 inches of thickness. Codes for residential applications often cite a 6 mil (0.006-inch thick) minimum vapor barrier. However, we recommend a 10 mil or higher for crawl space applications.
- Perms: The perm rating represents how readily water vapor will pass through a material. The lower the perm rating, the less permeable the material is.
- To classify as a vapor barrier, a material must have a perm rating of 0.1 or below. Poly sheeting that is 6 mils (0.06 perms) and thicker meets this bare minimum.
Choosing a Crawl Space Vapor Barrier Thickness
The thickness of the poly you choose will mainly depend on two factors:
- Utilization of the crawl space (storage, maintenance, etc.)
- Soil and ground conditions of the floor in the crawl space
Learn more about which vapor barriers are most suitable for the various conditions found in crawl spaces in this product comparison chart below.
Generally, if the crawl space is going to be entered regularly for maintenance, or if items are going to be stored in the crawl space, it is a good idea to get a thicker poly starting at 12 mils. The minimum 6 mil is inadequate if the floor of the crawl space has rocks, roots, or concrete chunks. Remember that one tear or puncture in your vapor barrier will allow moisture to pass through and render the barrier less effective.
To save cost without sacrificing durability, you can use a thinner poly, such as a 6 mil or an 8 mil, on the walls of the crawl space while using a thicker poly on the floor.
