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.
Shop Our List of Top Crawl Space Liners
All of Americover’s vapor barriers are string-reinforced 100% virgin poly.
6 mil String-Reinforced Crawl Space Liner
String-reinforced 6 mil is an economical choice when the overriding concern is cost. However, 6 mil is not recommended for areas where there will be activity or there are rough surfaces.
8 mil String-Reinforced Crawl Space Liner
String-reinforced 8 mil works well over soils made of dirt, mud, clay, or sand. Our 8 mil is frequently used on the walls in conjunction with a heavier material on the floors.
Pro Crawl Barrier is a 10 mil, Class 1 Vapor Barrier with a high gloss white finish. This option offers low permeability for excellent moisture protection. Because the 10 mil Pro Crawl Barrier is manufactured with virgin polyolefin-based resins, it has a high tensile strength and superior puncture resistance to small rocks.
12 mil String-Reinforced Crawl Space Liner
Because of its puncture resistance, string-reinforced 12 mil is great for soils that are rough or contain small rocks or tree roots, or for crawl spaces where there will be light or moderate activity. This film is an excellent choice when you need to strike a balance of economy and quality.
Pro Crawl Anti-Mold Vapor Barrier with MPT™
Pro Crawl Anti-Mold Vapor Barrier is a class 1 vapor barrier that passes ASTM E1745 class A, B, & C. Its perm rating blocks more vapor transmission than the leading competitor’s 10 mil vapor barrier with a permeance of only .022 perms.
20 mil String-Reinforced Crawl Space Liner
String-reinforced 20 mil is one of the thickest and toughest films on the market. It is great for commercial applications where an extra heavy-duty product is required. Its puncture resistance makes it great for use over soils that are hard or contain large rocks or broken concrete. Our 20 mil is the best product to use where there will be heavy activity.
Seal the Job with Vapor Barrier Tape
Tape is an essential part of the vapor barrier installation process, as you’ll need it to overlap panels and seal the material to the wall. We generally recommend two types of tape for crawl space applications:
- Vapor Tape can be used to create a waterproof seal and a clean finish. The general rule of thumb with vapor tape is one roll for every 1,000 square feet of vapor barrier. Make sure to allow for extra if you have multiple pylons or piers, which will require skirting, and therefore more vapor tape.
- Butyl Tape is an aggressive, self-healing, double-sided tape used to adhere the crawl space liner to the wall and seam the overlapping vapor barrier panels (where applicable). The amount of butyl tape you’ll need is based on the perimeter of the entire space, including any columns. We highly recommend a reinforced Butyl tape, so it does not stretch during application. And like Vapor Tape, allow for extra if you have multiple pylons or piers that require skirting.
In addition to tape, you’ll need fasteners to keep the vapor barrier attached to the foundation wall. We recommend our Christmas Tree Ratchet Fasteners — they can be easily installed with a drill bit every 18-24 inches through the butyl tape, creating an airtight seal around the hole.
Do you have questions about deciding which crawl space vapor barrier is right for your project? Call to speak with an Americover representative today at 760-388-6294 or email us at sales@americover.com.
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