A vapor barrier roll, staple gun, and some staples resting atop a piece of plywood

Moisture and vapor barriers are two terms that are often used interchangeably in the construction industry—but they’re not the same thing. 

Homeowners and constructors usually come across the moisture vs. vapor barriers debate. Although the ultimate purpose of both is to keep moisture outside of a building, whether it is liquid moisture (e.g., rain) or water in its most discrete form (e.g., vapor), more clarity is needed to differentiate their meaning. 

There’s no denying that both materials are used to resist water penetration – the key reason these two words are almost always used interchangeably – but it is imperative to understand that the reasons each material is used differ. 

Keep reading to learn what those reasons are and to unravel the confusion for a decision that is best for your home.

What Is A Moisture Barrier?  

It is a scientific fact: the presence of water in a confined area (e.g., crawl space) can lead to corrosion and mold. When water (or any moisture) comes in contact with the internal surface of metal jacketing or any insulation type, severe structural damage occurs. 

This phenomenon is pertinent to all temperatures (cold or hot) and among all home building applications—irrespective of which metal jacketing or insulation type you use. 

This instance is where a moisture barrier can help. 

Moisture barriers are layering of plastic films (available in other materials) that are used to prevent water from seeping inside the wall cavity and floors. The material is applied to help avoid crevice corrosion or pitting of the innermost surfaces of your building. 

A moisture barrier installed on a basement floor in a home
Courtesy of Eco Design Advisor

A moisture barrier also reduces galvanic erosion between dissimilar metals, such as pipes, tanks, jacketing, etc. To keep moisture from causing severe structural damage, the barrier must be water-resistant, durable, scratch-resistant, and sturdy. 

Some common moisture barriers include paper or aluminum-faced fiberglass roll insulation or polyethylene sheeting. Foil-backed wallboards are another popular type.

What Is A Vapor Barrier?  

Water in all its forms can have destructive effects when it invades an insulation system. Why? Because when moisture absorbs into the insulation, it can substantially impede the insulation materials’ overall thermal performance. This situation is where vapor barriers come in handy. 

High-performing vapor barriers keep water and its vapor out of the insulation system and prevent moisture from migrating into your space. They create a continuous encapsulation for a tighter building envelope while preventing moisture invasion and accumulation into the insulation system. 

Most importantly, a vapor barrier resists water vapor transmission into the insulation system from the humid and warm ambient surroundings to the cold pipe. This material is applied to external surfaces of an insulation system at the factory or right there and then. 

High water resistance, durability, low permanence, and flexibility are crucial vapor barrier properties.

What Can Moisture and Vapor Barriers Do For You?  

Good quality and high-performing barrier materials can serve numerous practical purposes, including:  

  • They can improve your home’s overall energy efficiency, lowering cooling and heating bills.
  • Properly installed barriers can help control the moisture that enters your home, making it more comfortable. Plus, excessive moisture in your space can contribute to mold growth.
  • Homeowners can use these barrier materials to patch insulation wear and tear for improved indoor air quality.
  • Both moisture and vapor barriers can increase the longevity of your house by preventing severe structural damage and mold growth. 
  • Stopping vapor diffusion.

Where Are Moisture and Vapor Barriers Used?

Vapor and moisture barriers will control the moisture levels throughout a building, including walls, crawl spaces, basements, and attics. 

A vapor barrier installed in a wall before the insulation and drywall is added.

You might be familiar with house wraps since they are visible on new home construction sites. They are also popularly used to prevent moisture from seeping into wall systems. 

Apart from securing walls from water intrusion, homeowners can also install barriers to prevent moisture from entering their home’s flooring. In such a case, barriers are installed over a concrete subfloor before the final floor is installed. Or else, water will move through the concrete and eventually seep into the flooring.

Moisture and Vapor Barrier Pros & Cons 

Instead of just highlighting the advantages of moisture and vapor barriers, we have also closely examined their shortcomings in this post. The purpose is to equip you with all the necessary knowledge to help you make an informed decision that’s best for your house’s needs. 

Here are the most notable benefits and drawbacks of both barrier types: 

Advantages of Moisture and Vapor Barriers

Structural Protection

The foundation of any building is critical to its soundness and structure. Any moisture in a crawl space can trigger wood rot, especially on beams and joists. 

Eventually, it will lead to significant structural damages, resulting in huge repair bills. Installing a high quality moisture or vapor barrier can limit moisture invasion to protect your home’s structural integrity.

Temperature Regulation 

Moisture invasion can also impact your home’s overall temperature, making it too cold, hot, dry, or stuffy depending on the season, weather, and numerous other factors. This result is because moisture either prevents the warmth from escaping your house or absorbing it. 

Thus, your furnace or HVAC unit will be forced to run for too long to maintain a stable indoor temperature. Installing a barrier covers those gaps and keeps excessive moisture out of your home for an adequately regulated temperature level.

Avoidance of Pest Invasions

An unsealed home (especially areas like crawl spaces) is an open invitation to wildlife and pests searching for food, water, and shelter. Once inside, these tiny creatures can wreak significant havoc on your home and your health. 

For instance, rodents can gnaw on electrical wires and wood fittings. In addition, insects and roaches can access your entire home from one unprotected area, posing probable health risks to you and your loved ones. 

Using barriers can completely shut down entry points and protect your home from uninvited invasions.

Pipe Defense 

Certain areas in your home, such as crawl spaces, comprise several pipes that supply power and water. When moisture invades such spots, it can cause corrosion around and inside these pipes, forcing them to break or burst over time. 

Moisture and vapor barrier installations can keep the pipes dry, ultimately increasing their life and preventing costly repairs. 

Disadvantages of Moisture and Vapor Barriers 

Despite the numerous benefits of vapor and moisture barriers, there are several significant drawbacks to consider.

The disadvantages include:

Additional Cost 

This is the most apparent drawback of barrier installation. On average, you can expect to pay $1,500-$15,000 for having barriers installed in a crawl space. 

The final price depends on the size and condition of the area covered, supplies used, and the labor involved. Moreover, a few additional costs might also arise during the encapsulation process.

A serviceman installs a vapor barrier on the ceiling in a basement

Greater Maintenance 

Since you will no longer be ignoring your crawl space, you will have to look after it just like you do for any other part of your house. This will involve regular inspections of your yearly home upkeep list to ensure the encapsulated area stays well maintained and adequately insulated.

Potential Upgrades 

Once moisture or vapor barriers have encapsulated certain areas of your home, air movement through the indoor space might feel more restricted, indicating your HVAC system might no longer be as efficient as earlier. 

If your home no longer feels as cool or warm as it used to before the barrier installation, you might have to upgrade your HVAC system for maximum comfort.

Moisture vs. Vapor Barriers: Final Note 

Both moisture and vapor barriers play a crucial role in creating a building envelope that’s healthier and more energy-efficient. In addition, good quality and high-performing barriers can help homeowners prevent structural damaged and unhealthy mold.

Are you still confused about which material to choose out of the two for your home construction needs? 

Here’s a quick refresher: 

  • A moisture barrier functions to aid in blocking water from seeping inside the wall cavity.
  • A vapor barrier is primarily responsible for stopping vapor diffusion by filtering water vapor (from inside your building) through the wall and condensing it with an insulation’s warm side.

Now that you know what a vapor barrier and moisture barrier stand for, you can easily choose the appropriate material for your home building needs. 

Just remember one thing—both of these materials hold the power to create an uninterrupted barrier for a tighter building envelope while reducing moisture intrusion and accumulation into an insulation system.

For more helpful guides on vapor and moisture barriers, their types, popular products, and other home-building projects, check the rest of our blog section. We strive to ensure every reader is equipped with all the necessary knowledge to make the best decision for them. 

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