In most cases, crawl space vapor barriers should be at least 12 mils thick poly, but it depends on the floor, how often the crawl space will be entered along with if the crawl space will be used for storage. The minimum 6 mil is inadequate if the floor of the crawl space has rocks, roots or concrete chunks. Below, we will explain everything you need to know about making this choice and how to purchase the right vapor barrier.
Crawl spaces beneath houses are usually vented, meaning they have small openings to let air pass freely between the crawl space and outside. However, this is not the primary source of moisture problems. Moisture is present in the ground soil beneath the house and in general these vents don’t do a good job of circulating air. 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 or encapsulated with the proper installation of a crawl space vapor barrier.
What Is A Vapor Barrier?
When applied correctly to your crawl space, a vapor barrier serves as a protective layer between the ground and the interior of your home. Its main purpose is to prevent moisture from seeping into the crawl space, which can lead to structural damage, mold, and even exposure to harmful gasses such as radon.
Related Article: Radon Vapor Barrier: Where Does It Go in a Radon Mitigation System?
Why a Crawl Space Vapor Barrier?
In addition to water vapor and mold prevention, there are significant benefits to using a crawl space vapor barrier. Sealing off your crawl space can prevent rodents, bugs, and other pests from making their way into your home. Moisture creates a hospitable environment for undesirable guests, and if left unaddressed, it 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 provide significant energy savings – an added plus if you ask us. But not every vapor barrier is built the same, and depending on your unique situation, you may need different levels of mil thickness and perm rating.
What Is Mil Thickness?
Mil thickness is a unit of measurement that determines the durability and puncture resistance of your vapor barrier. 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.
Depending on the environment underneath, and the expected level of use of your crawl space, you may warrant different levels of protection. For example, if you’ve got a crawl space that has fine soil underneath, and little to no foot traffic in its anticipated future, a 6 mil vapor barrier may do the trick. However, if you’ve got a lot of large, sharp rocks and think there’s a good chance you’ll be storing things down there or have to maintain equipment located in the crawl space, then a thicker barrier could be a better option due to durability concerns.
Standard 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. There are thicker options available, but not required. Our customers often opt for at least an 8 mil thickness to ensure the longevity of their crawl space vapor barriers, but to get the best recommendation, you should contact our product experts to discuss your specific needs.
What Is A Perm Rating?
Other than the mil thickness, the other important unit of measurement to look for on a vapor barrier is its perm rating. While ‘Mils’ is the measurement of the poly’s thickness, “Perm” represents its permeability to moisture.
The perm rating tells us how readily water vapor will pass through a material. The lower the perm rating, the less permeable that material is. To classify as a vapor barrier, a material must have a perm rating of 0.1 or below. Our vapor barriers that are 6 mils (0.06 perms) and thicker meet this bare minimum, but a thicker material provides a little extra protection along the way.
How Much Does A Crawl Space Vapor Barrier Cost?
The amount you’ll need to spend on a crawl space vapor barrier boils down to four main factors:
Permeability:
Thicker barriers typically have lower permeability, meaning they are less likely to allow moisture to pass through. These also come with a cost, however, with thicker materials being more expensive.
Ground Conditions:
High-traffic crawl spaces may require thicker barriers to withstand wear and tear, especially if you have uneven or rocky soil underneath the vapor barrier. Stronger materials come with a cost, but in our experience, it’s well worth the investment.
Virgin Vs. Regrind:
Not all polys of equal mil thickness and perm rating are built the same. Oftentimes, the type of poly that’s stocked at local hardware stores may be non-reinforced or made from recycled “regrind” materials. Regrind poly can contain impurities such as dirt or other contaminants, compromising its quality and longevity. Ultimately, contacting one of our product experts to determine your application’s needs is what’s best for your crawl space.
Total Area:
Of course, we all want to use the highest-quality materials everywhere in our home, but the truth is that the larger your crawl space is, the more you’re going to have to pay. Though going with a thicker vapor barrier generally comes at a higher cost upfront, it’ll also offer greater long-term value and durability. To save cost without sacrificing durability, you can try opting for 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.
Related Article: How Much Does a Crawl Space Vapor Barrier Cost?
Choosing The Right Crawl Space Vapor Barrier
Every project is unique, and we recognize that not everyone is going to warrant the same solution. Learn more about which vapor barriers are most suitable for your situation by using our 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.
We know this is a lot to consider – but the team at Americover is here to help. If you have any questions at all, please don’t hesitate to reach out to our vapor barrier experts today at 760-388-6294.
Shop Our List of Top Crawl Space Vapor Barriers
All of Americover’s vapor barriers are string-reinforced 100% virgin poly.
Our VaporBlock® Plus™ 20 Mil Vapor Retarder/Gas Barrier is one of the most effective barriers in the building industry today. It far exceeds ASTM E-1745 Class A, B, and C requirements and is formulated specifically to block radon gasses.
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 White/Black Dura-Skrim® 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 between economy and quality.
Pro Crawl Anti-Mold Vapor Barrier with MPT™ 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 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:
Our 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.
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.
Fasteners are necessary 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.
Find The Right Crawl Space Vapor Barrier With Americover
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, email us at sales@americover.com.
As an Americover customer, you will receive the personalized support of a dedicated account manager to simplify the ordering process and ensure the best solution for every one of your projects.
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