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Crawl Space Encapsulation vs. Vapor Barrier

Crawl Space Encapsulation or a simple vapor barrier?  What’s the better solution for your crawl space?  In the Southeastern United States, and in particular Atlanta, GA there is really only one solution.  Encapsulate every crawl space.

WAIT – before you stop reading – lets go over the reasons why this is important:

  • MOLD

50% of the air in your crawl space will find it’s way into your home.  This is based on the stack effect or the chimney effect of structures and is part of building science.  As houses get more insulation, better windows, tighter doors and overall energy efficient – they actually work against an open crawl space.

In the early days a crawl space would be so drafty that mold was not a problem.  Mold needs 3 things – temperature, humidity and a food source.  Crawl spaces (and basements) can easily have air with temps in the high 70s and humidity levels in the upper 50s, 60s, 70s and 80s…So the conditions are perfect for mold with wood under a house acting as a food source.  Back when houses were drafty there was so much air turnover that even when these conditions existed there was little opportunity for mold growth.

But now – all 3 conditions still exist but the house doesn’t turn air over nearly as fast, and with less air movement there is stagnant moist air – a great opportunity for mold.

Simply put there are steps you need to take to reduce the humidity in your crawl space (and for important reasons beyond just mold growth).

  1. If you don’t have a vapor barrier this is the first step, but not the only step.   This vapor barriers need to be the right classification (not any plastic will do) and be overlapped and taped at the seams to provide full coverage of your floor.
  2. Seal off the openings (warning: read number 3 before stopping here).  When high temp, high humidity air enters a cool crawl space you actually increase the relative humidity – so yes – by venting a crawl space you are actually making things worse.
  3. Monitor and correct any humidity issues:  This can be done in many different manors with the most common being the installation of a dehumidifier.  The better and more efficient dehumidifiers are April Aire and Santa Fe.  You can use other methods as well.
  4. Consider a full encapsulation option:  This is a big step towards making your crawl space a clean area and reducing the amount of work your dehumidifier does (in fact – without a vapor barrier on the walls you may be causing more moisture to enter the crawl space since moisture is looking for a dry place so your efforts may cost you more energy without installing a vapor barrier on the walls.  Crawl Space Encapsulation is installing the vapor barrier, closing off the vents, and wrapping the walls/columns in the crawl space.  This protect moisture from concrete columns, concrete walls and is the best way to keep your space dry.  (some homeowners do not need a dehumidifier after doing this option -but each house is different).
  5. Consider insulation – Closed cell spray foam insulation can be used as a vapor barrier (closed cell does not allow water penetration) and insulation on the interior walls of a crawl space.  You then get the benefit of an insulation space without adding batt insulation to the underfloor area.  Since it’s closed cell you have the added benefit of moisture barrier and insulation.  This is considered to be the “cream of the crop” solution for homeowners.


Whatever you decide – there are multiple ways to accomplish this – but understand that depending on your situation many factors can change what is best for your situation.  Just remember – in the southeast – a vapor barrier is rarely enough to keep your home healthy and energy efficient.

Contact us for further questions or if you have a space you want evaluated.  404.662.2454 or info@foundation-worx.com

Jonathan Maguire is the Owner and Systems Engineer for Foundation Worx, LLC. Atlanta's full service foundation repair company.

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