Vapor Barriers

vapor barrier

This is A Example of A Professional Vapor Barrier 

Table of Contents

What is a Vapor Barrier?

Vapor barriers, or crawl space vapor retarders, are materials used to protect buildings and other structures from the damaging effects of moisture. They do this by preventing the passage of water vapor into wall, ceiling and floor assemblies. When installed correctly, these materials act as a protective layer against water infiltration that can lead to mold growth, mildew odor, and structural damage.

Vapor barriers are usually plastic sheets or membranes installed on the basement or crawlspace floor going midway up the foundation walls. There are also whole-house vapor barriers that are usually installed when a new home is built. These vapor barriers cover all the the building with specific sealing around the windows. It is prohibitiavley expensive to install this type of barrier in an existing home unless all of the outside materials are removed.

When a dirt crawlspace is wet, toxic levels of mold can grow and infiltrate the living spaced above. To prevent this problem, a .6ml or above fireproof plastic vapor barrier is installed. This vapor barrier will cover the entire floor area and go midway up the foundation walls. There are other types of materials used in vapor barriers; reinforced poly sheeting is a type of vapor barrier material that includes a polymer material that is reinforced. Extra lawyers of fabric are used and it is designed to provide more protection than the standard .6ml poly sheeting. It is flexable and will provide and tight fit around the crawlspace walls thus providing an very tight seal. 

This type of vapor barrier will keep indoor heated air inside during cooler months. Vapor barriers are essential for keeping moisture from entering wall assemblies. If the crawl space has drainage problems a sump pump may also be necessary.

When a vapor barrier is not present, moist air can enter the walls, leading to condensation and potential toxic mold growth. In addition to preventing moisture infiltration, vapor barriers can also help reduce energy costs by keeping warm air inside the building during winter months and cool air inside during summer months. Installing a vapor barrier helps reduce the amount of energy required for heating and cooling systems to maintain comfortable temperatures throughout the year.


In addition to installation of vapor barriers, proper ventilation is also essential for controlling moisture and preventing mold growth in buildings. Ventilation helps reduce humidity levels and prevents warm, moist air from collecting inside wall assemblies. While ventilating alone is not enough to protect a building from water infiltration, it is essential for keeping moisture levels in check and maintaining a healthy indoor environment.

Regularly inspect the area to ensure vapor barriers remain intact and continue to protect the structure from the effects of moisture. Proper ventilation must also be provided in order to reduce humidity levels and keep moisture out of the building’s interior. When these two elements are combined, a structure will remain safe and comfortable year-round.

Do vapor Barriers Work?

The effectiveness of a vapor barrier depends on its location within the building structure and its ability to completely seal the building envelope. For maximum protection, the vapor barrier should be installed on the foundation walls. Sometimes the ceiling of the crawl space is also sealed with plastic. It is important that there are no gaps or openings in the vapor barrier to allow moisture to enter. If a gap exists, it must be sealed with an appropriate sealant.

Average Costs in the Bay Area

The cost range in the San Francisco Bay Area is between $1500 and $5000. Please always get three quotes before signing an agreement for this type of work. Check references, licenses, and insurance. Make sure your guarantee is in writing.

And Finally

Vapor barriers can significantly reduce the risk of water infiltration and mold growth in buildings. When installed correctly, they provide an effective shield against damaging moisture instrusions while also helping to reduce energy costs. They must be maintained; a monthly inspection is recommeded to check for unplanned water intrustions or any breaches in the plastic. This is especially important if you are also running a sump pump. Always check the outflow from your sump pump so that it does not flood your interior areas – if the drain is blocked on the outside by debris, it will force water back inside your protected areas.