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All You Need To Know About Vapor Barriers – Why You Might Need Them? Installation Cost? etc.)

Moisture control is crucial for home maintenance, and one of the most important tools for keeping moisture at bay is a vapor barrier. As such, you may wonder what a vapor barrier is. Do you need one? 

A vapor barrier prevents vapor diffusion. It can prevent mold and mildew, lessen electrical hazards, protect pipes, prevent rodent infestation, and control temperature. On average, installing vapor barriers can cost $1,200 to $4,000. While it can be beneficial, it isn’t always necessary. 

In this article, I’ll discuss what you need to know about vapor barriers. Is it necessary? How much does it cost? What are its benefits? 

What Is a Vapor Barrier and Why Do You Need One?

A vapor barrier is a foil or plastic sheet that prevents vapor diffusion through building materials. It inhibits condensation in various building assemblies, such as floors, roofs, walls, and foundations. 

Moisture flows from an area with a high concentration to a place with a lower concentration. It travels along with air, reaching different parts of your home. If it’s humid or moist, it can affect building materials. Hence, you need a sound moisture management strategy, and that is where vapor barriers can help. 

Vapor barriers have various applications, whether it’s air sealing an attic or limiting moisture in walls. It’s crucial to note that its installation depends on many factors, such as the climate in your area. 

Read: What Does Air Sealing An Attic Mean?

Types of Vapor Barriers 

The effectiveness of vapor barriers depends on several factors, including material. The vapor barrier’s material determines the transmission rate or permeance, which affects the amount of water vapor that transfers into a surface area. 

You must find one that matches your needs. It’s often thin and film-like, while others can be thicker. For industrial applications, thicker materials are better. Below are some of the most common materials

  • Glass
  • Rubber membrane 
  • Polyethylene sheet 
  • Sheet metal 

Reasons To Install a Vapor Barrier 

  • Mold and mildew prevention: Damp environments can be health hazards. They can cause wheezing, stuffy noses, and itchy eyes. It’s hazardous for people with asthma. Installing a vapor barrier can help limit moisture and dampness. 
  • Minimize electrical hazards: Moisture can make wirings weak. In turn, damage to wires can increase the risk of electrical shock and similar dangers. That’s another issue that vapor barriers can lessen. 
  • Protect pipes: Gas and water pipes might be more prone to damage when they’re often moist. Leaks can be disastrous and costly. Hence, installing vapor barriers can protect against pipe rust and rot. 
  • Prevent rodents and insects: Infestation is common in moist environments. Rats and bugs love high humidity. One thing that can help manage their presence is installing a vapor barrier. 
  • Control temperature: Moisture influences humidity and temperature. It can make your home cooler or warmer than necessary. Using vapor barriers will not only help in temperature management to make your home more comfortable, but it can also promote energy efficiency.  

Read: What Is The Best Way To Insulate A Crawl Space With A Dirt Floor?

Who Needs Vapor Barriers? 

Despite the many benefits of installing vapor barriers, it’s not necessary for all homes or buildings. It can be a waste of time and money for some people, especially when it isn’t done correctly. Below is a rundown of some situations that warrant a vapor barrier. 

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Those Who Experience Extreme Temperatures 

Vapor barriers can be beneficial if you live in an area with frigid temperatures, especially in the winter. For optimal results, install the vapor barrier in the insulation’s interior. The exterior side must remain permeable, which is crucial for dissipation. 

Vapor barriers are also necessary if you live in scorching-hot and humid locations. In such instances, the best place to install a vapor barrier is on the exterior of your insulation. It can prevent outside humidity from penetrating into the walls. 

Read: Do I Need To Remove Old Attic Insulation Before Installing New?

Those Who Live in Areas With High Radon 

Breathing radon gas increases the risk of lung cancer. It’s odorless and colorless, which makes it even more dangerous. It isn’t a health issue outdoors since it disperses quickly. However, it can enter indoors through holes and cracks in a building’s foundation. 

Many of the people who install vapor barriers are those from high-radon areas. These barriers can restrict the entry of harmful chemicals into your home. If you’re from these areas, choose a vapor barrier that meets the minimum class recommendation to ensure effectiveness. 

Those Who Have Below-Grade Floors and Slabs 

The transmission of ground moisture is worse in below-grade floors and slabs, which are known for being damp and humid because of their locations. As such, you can benefit from using vapor barriers, especially before installing flooring or wood frames on concrete. 

Read: Do I Need To Remove Old Attic Insulation Before Installing New?

Those Who Have Old Homes 

Your home becomes more susceptible to damage as it ages, resulting in a weaker overall structure. Old houses and ductworks require more attention and maintenance. That’s another instance when people decide to install vapor barriers, preventing further damage that moisture and humidity might bring. 

The Cost of Vapor Barriers

Installing a vapor barrier can be costly, especially if you’re using high-quality materials and hiring highly-qualified professionals. Some people might make it a DIY task to save money, but you should not do such a task if you aren’t confident in your knowledge and skills.

On average, vapor barrier installation can cost between $1,200 to $4,000, including material and labor. 

One thing that can cause variations in cost is the thickness of the vapor barrier. Thicker materials are generally more expensive. They’re also better because they can provide better protection. Here’s a look at average prices depending on thickness: 

  • 6 mm (0.24 in): $.15 per square foot (0.09 square meter)
  • 8 mm (0.31 in): $.18 per square foot (0.09 square meter)
  • 10 mm (0.39 in): $.20 per square foot (0.09 square meter)
  • 12 mm (0.47 in): $.30 per square foot (0.09 square meter)
  • 20 mm (0.79 in): $.50 per square foot (0.09 square meter)

The size and condition of the area where you’re installing the vapor barrier can also affect costs. For instance, it can be more expensive if it’s a large crawl space with insufficient space to work on versus an easily accessible attic. 

Take note of the possible additional costs. For instance, if you already have an existing vapor barrier, its removal and replacement might cost more. Also, you might need to pay for permits and building licenses, depending on the requirements where you live. 

Vapor Barriers vs. Vapor Retarders 

A common misconception is that vapor barriers and vapor retarders are the same. However, the two are different. 

The permeability of the material is a major difference between the two. It’s the rate at which water vapor diffuses in a given material. When the perm rating is low, it’s difficult for water vapor to seep in, which makes it highly effective. On the other hand, a higher perm rating means water vapor can get in faster. 

A vapor barrier has a permeability rating of .1 or less. It’s an impermeable membrane. Meanwhile, a vapor retarder has a permeability rating of more than .1. It’s a Class II vapor retarder if the permeability is between .1 and 1.0, and a Class III vapor retarder’s rating is 1 to 10. Vapor barrier is a Class I. 


Vapor barriers are crucial for moisture management in homes or buildings. It can prevent mold and mildew, as well as rodent infestation. Nonetheless, it may not always be necessary, so consult an expert to know if you need it or if it’s an unnecessary expense.