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Should Crawl Space Insulation Have a Vapor Barrier?

A crawl space vapor barrier is essential for preventing moisture buildup. However, it is important not to confuse the vapor barrier with crawl space insulation. Both components are necessary if you want to control the climate underneath and inside your home.

REenergizeCO provides professional crawlspace insulation for homeowners in Denver, Fort Collins, and throughout the Colorado Front Range. We can explore the benefits of adding a vapor barrier, insulation, and/or air sealing to make your home more efficient and bring your utility bills under control.

What Is a Crawl Space Vapor Barrier?

A vapor barrier is a material installed within a crawl space to prevent moisture from getting in under your home and affecting the structure of the house above. The primary function of a crawl space vapor barrier is to prevent water vapor from the ground or surrounding soil from seeping into the crawl space.

What Is Crawl Space Insulation?

Crawl space insulation is a material or combination of materials installed in the subfloor area beneath a building, typically between floor joists or along the perimeter walls of the crawl space. Its primary purpose is to enhance energy efficiency by reducing heat transfer between the crawl space and the living spaces above, as well as to mitigate moisture issues and improve indoor air quality.

Read More: Do I Need to Insulate My Crawl Space?

Do You Need a Vapor Barrier for Your Crawl Space?

Crawl space insulation and a vapor barrier serve distinct but complementary purposes. Insulation improves energy efficiency, but it doesn’t help with the moisture levels inside the crawl space.

With 33% average humidity, weather conditions in Colorado are usually dry. But crawl spaces tend to be damp regardless of the local climate. As such, a vapor barrier is typically necessary for managing moisture levels—even in a dry, cool climate like Colorado’s.

Is a Vapor Barrier Worth It in a Crawl Space?

Insulating the crawl space can make the floors above more comfortable and enhance the overall energy efficiency of your home, resulting in lower monthly utility bills. The benefits of installing a vapor barrier include:

  • Preventing mold growth, wood rot, and corrosion of metal components
  • Improving your home’s indoor air quality
  • Protecting insulation from moisture damage
  • Extending the lifespan of wood framing, subflooring, and other building materials
  • Deterring rodents, insects, and other pests, which helps prevent infestations

The process of installing both insulation and a vapor barrier is known as encapsulation. We recommend encapsulation no matter the type of insulation used in the crawl space. 

What Type of Vapor Barrier Is Best for the Crawl Space?

Reinforced polyethylene plastic sheeting is the most effective vapor barrier for crawl spaces. It’s durable, easy to install, and provides an effective barrier against water vapor.

There are other options, such as vapor barrier membranes designed specifically for crawl spaces and reinforced vapor barriers. As a rule, these are really only necessary when the crawl space terrain is rough or additional durability is needed.

Plastic sheeting may seem easy to lay down yourself, but we recommend professional installation. This will ensure that there are no gaps or tears in the crawl space vapor barrier and the plastic is securely fastened along the walls of the crawl space, support beams, and other components.

Do You Need a Vapor Barrier Over Insulation?

The vapor barrier complements the crawl space insulation. It helps contain moisture from the ground underneath your house, preventing drafts, air quality issues, and damage to building materials (including insulation). However, insulation in the crawl space should not be covered by the vapor barrier.

Covering the insulation in plastic will trap cool air and moisture particles, which can damage the insulation material over time. If moisture is a concern, it is best to install faced insulation (batts of insulation with a built-in vapor barrier) along the walls of the crawl space.

How Thick Should a Crawl Space Vapor Barrier Be?

The minimum recommended thickness for poly plastic sheeting is 7 mil (that’s 7 one-thousandths of an inch). If you access the crawl space regularly, use it for storage, or the floor has rocks and other objects that can puncture the plastic, thicker sheeting (up to 20 mil) may be necessary.

Can I Install a Vapor Barrier Myself?

Yes, you can. The bigger question, though, is should you install it yourself.

Potential issues that may arise if you try to install a vapor barrier on your own include:

  • Inadequate Sealing: Properly sealing seams and overlaps in the vapor barrier is crucial for preventing moisture infiltration. DIYers may struggle to achieve airtight seals, leading to gaps or tears that compromise the effectiveness of the barrier.
  • Poor Coverage: Ensuring thorough coverage of the crawl space floor is essential for controlling moisture levels. Overlooking certain areas or failing to extend the barrier up the walls can leave vulnerable spots where moisture can enter.
  • Difficulty in Access: Crawl spaces are often cramped, dark, and challenging to navigate, making installation tasks more difficult. Limited space and accessibility can hinder the ability to maneuver and properly install the vapor barrier.
  • Tear or Puncture Risks: The crawl space environment may contain sharp objects, debris, or rough surfaces that can puncture or tear the vapor barrier during installation. Non-professionals may inadvertently cause damage to the barrier, compromising its effectiveness.
  • Moisture Trapping: If moisture is trapped between the vapor barrier and the crawl space floor or walls, it can lead to condensation, mold growth, and other issues. Improper installation techniques may inadvertently trap moisture, exacerbating the problem.
  • Insufficient Ventilation: Proper ventilation is essential for maintaining optimal moisture levels in the crawl space. DIYers may overlook the importance of ventilation or fail to provide adequate airflow, leading to moisture buildup and potential issues with humidity control.
  • Safety Hazards: Working in a crawl space can pose various safety risks, including exposure to mold, pests, hazardous materials, and physical hazards such as tripping or falling. Homeowners may lack awareness of these risks and fail to take appropriate safety precautions.

Home insulation professionals have the experience, knowledge, and equipment to avoid all of these issues. Generally speaking, hiring a professional crew results in a vapor barrier that is properly installed and effective.

How Much Does a Vapor Barrier in the Crawl Space Cost?

The cost of a vapor barrier depends on the size of the crawl space. More square footage means more time and labor to complete the installation. Specialized materials (such as vapor barrier membranes and encapsulation systems) are more expensive and take longer to install, resulting in additional cost.

For optimal results, it is important to consider professional installation. Reputable contractors should be able to provide you with a transparent quote tailored to your specific requirements.

View Our Pricing Guide

Need a Crawl Space Vapor Barrier? REenergizeCO Can Help!

Colorado has a dry climate, but moisture can still have a negative impact on your home. A combination of crawl space insulation and a vapor barrier can make your home more energy-efficient and affordable, as well as create a pleasant and healthy environment.

REenergizeCO provides professional crawl space insulation and vapor barrier services to customers in Denver, Fort Collins, and all of the Front Range. Contact us today to find the best solutions to lower your utility bills!