Vapor Barriers: Home Inspector Fact and Fiction

Vapor barriers are often recommended by home inspectors when moisture or evidence of moisture is observed in a crawlspace area.  This is particularly true in many areas of Sonoma County including Petaluma, Santa Rosa, Cotati, Rohnert Park and other low lying areas with adobe soil.  In many of these situations I see vapor barriers being recommended when there is evidence of standing water. When standing water is observed during a home inspection a vapor barrier is not the proper recommendation by the home inspector and in certain circumstances recommending the vapor barrier will exacerbate the problem.  In this post I will discuss some facts about vapor barriers and some of the fictions associated with vapor or moisture barriers.

Fact:  Vapor barriers are vapor proof.  This is a true statement.  Vapor is liquid in a gaseous form and plastic (usually polyethylene) vapor barriers are effective at preventing vapor from passing through the plastic.  A good recommend from your home inspector is made when general dampness is observed with no evidence of standing water.

Fiction:  Vapor barriers water proof crawlspace areas.  This is not a true statement.  All too often I see home inspector make recommendations for vapor barriers when the real solution is improvements to lot grading and drainage.  Water is different than vapor and polyethylene plastic on the ground is not water proof.  When actual water (in liquid form) is entering or collecting in a crawlspace area vapor barriers are not a effective solution.  In these conditions the water will collect on the plastic and slow the process dissipation.

Fact:  Vapor barriers are a good solution for minor dampness due to poor ventilation.  This is a true statement.  Vapor barriers can be an effective solution when limited ventilation is present and minor general dampness is observed.  A vapor barrier will help get the vapor to the perimeter of the building where it can exit via a foundation area vent.

Fiction:  Vapor barriers are easy to install.  This is a fictional statement.  A good vapor barrier takes time and skill to install properly. Vapor barriers should be anchored to the ground so they do not have gaps when service personnel crawl through the sub area.  Vapor barrier seams should be overlapped at each junction to prevent vapor from escaping to then interior of the building.  And all transitions such as around internal piers should be sealed tight to prevent vapor from collecting in undesirable areas.

Steve Ramos Certified Home Inspector

Steve Ramos is a Certified Home Inspector, Mold Inspector and Building Science Thermographer.  He has over 10 years of home inspection field experience.  Steve has a very diverse and well rounded background.  His reports are detailed, accurate, and timely.  Steve has been featured on over 104 episodes of HGTV’s House Detective.  He offers his services in all nine Bay Area counties including:  Santa Rosa, Petaluma, Novato, San Rafael, Napa, Sausalito, San Francisco, Walnut Creek, San Ramon, Rohnert Park, Cotati, Bodega Bay, and Cloverdale.

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