Alexei Volkov
The thickness of a vapor barrier is an important consideration when installing a crawl space encapsulation system. Vapor barriers are typically made of polyethylene, a widely used plastic that helps improve air quality and decrease energy consumption in homes. The recommended thickness of a vapor barrier depends on various factors, including the type of floor, the intended use of the crawl space, and the presence of moisture and odors. Most crawl space vapor barriers should be at least 12 mils thick, with some sources recommending 16 mil or higher for better durability and protection against moisture and punctures. Thicker vapor barriers, such as the 20 mil option, are also available for heavy-duty applications and offer increased puncture resistance and reinforcement.
| Characteristics | Values |
|---|---|
| Minimum thickness for crawl space vapor barriers | 6-12 mils |
| Thickness for vapor retarders under concrete | 10 mil or thicker |
| Thickness to prevent radon and water vapour penetration | 20 mil |
| Thickness for crawl spaces | 12-20 mils |
| Thickness for interior slabs and garages | 6 mil |
| Thickness for exterior slabs | Not necessary |
| Thickness for floor covering | 10-15 mil |
| Thickness to walk on | Thicker than 6 mil |
| Thickness for puncture resistance | 20 mil |
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What You'll Learn
Crawl spaces: 6-12 mil is the minimum
A crawl space is the area between the floor of a house and the ground. Crawl spaces are usually vented, meaning they have small openings to let air pass freely between the crawl space and the outside. However, moisture is present in the ground soil beneath the house, and these vents don't effectively circulate air. In humid climates, moisture-laden air enters the crawl space and condenses into water droplets on cool pipes and concrete walls, promoting mould, fungus, mildew, and bacteria.
A crawl space vapour barrier is a plastic sheet that prevents water vapour, mould, and pests from entering your home. The ideal thickness of a vapour barrier depends on the floor of the crawl space, how often it will be entered, and whether it will be used for storage. The minimum thickness for a vapour barrier is 6 mil, but this is inadequate if the floor of the crawl space has rocks, roots, or concrete chunks. For crawl spaces, a vapour barrier should be at least 12 mil thick.
While thicker barriers are more expensive, they offer better moisture control, as their lower perm rating allows less water vapour to pass through, ensuring a drier, healthier crawl space. A thicker barrier will also be more resistant to tearing and punctures in high-traffic areas.
If you are unsure about which vapour barrier is right for your crawl space, you can contact a professional for advice.
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Radon barrier: 20 mil recommended
A radon barrier is a type of plastic sheeting used to block radon gas from entering a building through the crawl space. The thickness, or "mil", of a radon barrier is important as it needs to be thick enough to be impermeable to gases.
The recommended thickness for a radon barrier is 20 mil. This is much thicker than the minimum requirement for a vapour barrier, which is typically between 6 and 12 mil. A thicker barrier is recommended for radon mitigation as it needs to be impermeable and durable.
A 20 mil radon barrier is considered overkill for most systems and is only necessary if you are seeking to mitigate high levels of radon. A thicker barrier will also be more durable and easier to walk on, which is important if the crawl space is used for storage.
A radon barrier should be properly sealed with furring strips 12" up the foundation and the pylons must also be properly sealed. This will ensure that the radon gas cannot enter the building.
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Concrete slabs: 10 mil minimum
Concrete slabs require a minimum thickness of 10 mil for an effective vapor barrier. This is because thinner plastic cannot withstand the rigours of construction and is susceptible to punctures and tears, which can let water vapour into the slab.
Vapor barriers are essential to preventing moisture-related issues in concrete slabs. Moisture vapour can rise through porous concrete, causing mould, mildew, and fungus. Additionally, harmful gases like radon and methane can migrate through the slab, posing health risks.
The American Concrete Institute (ACI) recommends a minimum of 10-mil polyethylene for vapor retarders under concrete. This thickness exceeds the ASTM E-1745 standard and provides sufficient puncture resistance for residential construction. However, for laser screeds or heavy equipment, a thicker 15-mil barrier is recommended.
Concrete Vapor Barrier products, such as those offered by Farm Plastic Supply, are engineered from durable plastics and are available in 10-mil thicknesses. These products are perfect for residential installations and can effectively prevent water vapour transmission and related issues.
While 10-mil plastic is the minimum recommended thickness, it's important to note that thicker barriers offer better protection against moisture and punctures. For example, a 20-mil barrier can provide extra insulation and save on heating and cooling costs, while also offering increased puncture resistance, making it ideal for heavy-duty commercial applications.
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Thicker is better
Thicker is indeed better when it comes to vapour barriers. The thickness of a vapour barrier is measured in mil, which refers to the thickness of plastic sheeting.
The thicker the vapour barrier, the better it is at barricading against moisture and resisting punctures and tears. A thicker barrier will also be more durable when exposed to sunlight. A thicker barrier is also necessary if your crawl space floor has rocks, roots, or concrete chunks.
The American Concrete Institute (ACI) recommends a minimum of 10-mil polyethylene or thicker for vapour retarders under concrete. However, some sources recommend a thickness of 16 mil or higher, as this is considered impermeable in American building codes.
For crawl spaces, 20-mil vapour barriers are the thickest option and are perfect for encountering soil, large rocks, or broken concrete. They are also great for heavy-duty commercial applications.
It's important to note that while thickness is essential, other factors such as tensile strength, permeance, and string-reinforcement will also determine which vapour barrier is best for your project.
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Puncture and tear-resistant
When it comes to choosing a plastic vapour barrier, thickness is an important consideration. The thicker the barrier, the better it will be at resisting punctures and tears.
A vapour barrier should be at least 12 mils thick, but the minimum thickness depends on the floor of the crawl space and how often the space will be entered. If the crawl space has rocks, roots, or concrete chunks, a minimum of 6 mil is inadequate. Thicker barriers are better at resisting punctures and tears, so it is important to choose a thickness that is appropriate for the specific application.
For heavy-duty commercial applications, string-reinforced 20-mil plastic sheeting is a good option. It is thick, tough, and puncture-resistant, making it ideal for encountering soil, large rocks, or broken concrete. 20-mil barriers are also durable and long-lasting, reducing the likelihood of tears that would allow moisture to return to the crawl space.
Another option for a puncture and tear-resistant vapour barrier is to use a reinforced plastic sheeting product. Reinforced barriers incorporate a scrim reinforcement that enhances tear resistance and longevity. They are especially useful for high-stress environments where a standard barrier might not hold up over time.
In addition to thickness, it is important to consider the material and construction of the vapour barrier. Polyethylene is a commonly used material for vapour barriers because it is durable and has low permeability. To improve durability, some polyethylene barriers incorporate a woven pattern into the sheeting, which increases tensile strength.
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Frequently asked questions
The minimum thickness for a crawl space vapor barrier is 6-12 mils. However, thicker barriers are better at preventing moisture and resisting punctures and tears.
A 20 mil vapor barrier is the optimal choice for crawl spaces as it fully encapsulates the home from the earth below. It is also the thickest vapor barrier used in crawl spaces.
The American Concrete Institute (ACI) recommends a minimum of 10-mil polyethylene or thicker for vapor retarders under concrete. A 20 mil vapor barrier can also be used under concrete slabs to stop moisture migration and reduce mold, mildew, and fungus.
