Crawl Space Moisture Barriers in a humid crawl space illustrating how mold can take growth

Complete Guide: The Benefits of Vapor Barriers & Encapsulations

Crawl spaces play an integral role in maintaining the structural integrity of your home. Particularly in regions like the Middle Tennessee Area, which sees a substantial amount of rainfall, understanding the importance of crawl space maintenance is critical. This guide will delve deep into two prevalent methods used to protect these spaces – crawl space encapsulation and vapor barriers.

What are Moisture Barriers, and Why are They Important?

Moisture barriers play a critical role in maintaining the integrity of structures by preventing moisture damage. Their importance can’t be overstressed as they are essential in safeguarding your home’s building materials, which are often susceptible to mold and water damage​​. This susceptibility isn’t just a concern in hot, humid climates; even homes in cooler climates can benefit from the protection moisture barriers provide​​.

Restoration Technician Inspecting Crawlspace

So, what’s the solution? Enter moisture barriers.

Moisture Barriers Defined:

Moisture barriers are designed to protect buildings by blocking the passage of moisture, which can cause damage to structural components like walls and flooring. They are essential in preventing liquid water from entering the home and are recommended for areas such as exterior walls, crawl spaces, and basement floors to prevent ground moisture from causing problems like mold growth or structural weakening​​.

These barriers come in various types and permeability classes. Class I barriers are considered impermeable and include materials like polyethylene sheets, while Class II and Class III offer varying degrees of permeability, suitable for different climates and specific needs of a building​​.

Proper installation is crucial for the effectiveness of moisture barriers. For instance, ensuring proper ventilation in the home, using the right type of barrier for the specific conditions, and installing the barriers on the side of the wall most exposed to heat or moisture are important steps​​. Additionally, covering the entire surface area of a subfloor and sealing any gaps or openings with moisture-resistant tape is vital to prevent moisture intrusion​​. It’s important to avoid common installation mistakes such as using the wrong type of barrier for the climate or installing it on the wrong side of the wall, as these can lead to the barrier’s failure and potential mold growth within the walls​​.

Vapor Barriers Explained:

Vapor barriers are a specific type of protection in building construction that aims to prevent water vapor from permeating walls and insulation systems. These barriers, which may include heavy-duty plastic materials like a fortified 9mm variant, are applied to create a continuous shield, enhancing the building envelope and preventing moisture accumulation​​.

Moisture barriers differ from vapor barriers primarily in their application and permeability. Moisture barriers are designed to prevent liquid water from infiltrating building envelopes and are typically installed on the building’s exterior. They offer waterproofing, protect against hydrostatic pressure, and reduce the risk of mold by minimizing moisture and condensation within wall systems​​. Below-grade moisture barriers, which include liquid-applied membranes and various pre-formed sheet materials, provide additional protection for foundations against soil moisture​​.

Vapor barriers, on the other hand, are usually installed on the interior side of the frame to prevent water vapor from inside the structure from diffusing through the walls and insulation, a process known as vapor diffusion​. They are classified based on their permeability, with Class I having the lowest permeability and being considered impermeable. Class II and III barriers offer varying degrees of permeability and are selected based on the specific needs of the building and the climate​​.

The Essence of Crawl Space Encapsulation:

Crawl space encapsulation is a definitive approach to moisture management, involving the complete sealing of the crawl space with a heavy-duty vapor barrier, usually between 12mm and 20mm thick. This process transforms the crawl space into part of the home’s building envelope, ensuring a controlled environment that’s safeguarded against moisture and temperature fluctuations​​.

Crwalspace Encapsulation Cover Image
The crawlspace is entirely sealed with a heavy-duty vapor barrier, and then taped at all joints during encapsulation.

Key benefits of crawl space encapsulation include moisture control, which prevents mold growth and wood rot, thereby maintaining structural integrity and promoting better indoor air quality by stopping mold spores from circulating in the home​​. It also enhances energy efficiency, as the encapsulated area reduces the home’s heating and cooling needs, potentially saving homeowners up to 18% on energy costs​​. Additionally, it improves air quality by preventing the infiltration of allergens and pollutants, and by reducing radon gas entry, thus mitigating health hazards​. Finally, it increases HVAC efficiency and longevity by reducing the system’s workload​​.

The cost of encapsulation can vary, and the process generally takes 3 to 5 days to complete, including cleaning, insulation, and installing a dehumidifier, after an initial assessment​​.

How they work:

-Improved Air Quality: By blocking moisture, the risk of mold and mildew is considerably reduced.

-Energy Savings: With minimized moisture intrusion, your home’s energy efficiency improves.

-Cost-Efficiency: Given that it’s less labor-intensive, vapor barrier installation is generally more affordable than full encapsulation.

How Can We Benefit from Moisture and Vapor Barriers?

1. Energy Efficiency Enhancement: Implementing robust barrier materials can augment a home’s energy efficiency. This implies potential savings on those heating and cooling bills.

2. Moisture Control: When these barriers are installed correctly, they can regulate the moisture entering your home, fostering a more comfortable living environment. Let’s not forget the adverse effects of excessive moisture—like the dreaded mold growth.

3. Structural Longevity: Both barriers can significantly boost the lifespan of your residence by shielding it from potential structural damages and mold proliferation.

4. Diverse Application Areas: These barriers find their applications in various parts of a building, from walls and attics to crawl spaces and basements.

Assessing the Pros and Cons

Moisture and vapor barriers offer critical protection for the structural integrity of buildings but come with their own set of pros and cons​.

Crawlspace Encapsulation in Blue Image


  • Structural Protection: They prevent wood rot in structural elements like beams and joists, safeguarding the building’s foundation​​.
  • Temperature Regulation: Barriers help maintain stable indoor temperatures, reducing the need for excessive heating or cooling​​.
  • Pest Deterrence: Sealing off entry points with barriers keeps out pests that could damage your home or pose health risks​​.
  • Pipe Protection: By keeping areas around pipes dry, barriers prevent corrosion and extend the lifespan of plumbing​​.


  • Cost: Installing moisture and vapor barriers can be expensive, with prices ranging significantly based on the size and condition of the area​.
  • Maintenance: These barriers require regular inspections to ensure their continued effectiveness​​.
  • Potential HVAC Upgrades: Encapsulation may restrict air movement, necessitating upgrades to your HVAC system for optimal comfort​​.

Each factor should be carefully considered when deciding on installing moisture or vapor barriers.

Moisture vs. Vapor Barriers vs. Encapsulation: Wrapping Up

There are clearly many valid approaches to humidity and moisture control when it comes to crawlspaces and basement. While all these options serve the overarching purpose of protecting against moisture in its various forms, their functions differ.

To recap:

– Moisture barriers are pivotal for preventing water ingress into wall cavities.

– Vapor barriers counteract vapor diffusion by preventing water vapor from penetrating walls and merging with insulation.

-Encapsulation offers a comprehensive solution to combat moisture, energy efficiency, and insect intrusion by covering the crawl space, including its walls and floors with a heavy-duty vapor barrier and sealing all the joints.

Recognizing the distinctive roles of these barriers ensures that you’re equipped to make the right choice for your construction needs. Both materials can craft a seamless barrier, minimizing moisture intrusion and fortifying insulation systems. Armed with this knowledge, you’re poised to make informed decisions for your own home.

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