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June 27, 2019

Today, that is the question.  Many homeowners ask whether they should leave their vents open in the summer or not.  Confusion surrounds this issue because there are strong opinions on both sides.  To answer this question, Let's take a step back and address the science that impacts this decision.

We live in a hot humid climate.  Many people have issues with damp crawlspaces because when warm humid air contacts the cool duct system it creates condensation.  It can also create condensation on the insulation and pipes in the crawlspace.  When this moisture accumulates, it drips down onto the vapor barrier and can cause large pools of water in the crawlspace.

So, is the answer to close the vents? Many folks recommend that as a logical conclusion to the problem of outside humidity.  But the problem is that closing the vents doesn’t totally stop humidity entering the crawlspace.  Because heat rises, you will always have some air entering the crawlspace from the outside.  If the vents are closed, and moisture still gets into the crawlspace, it can’t easily get out.  You have the potential for that moisture to become trapped and cause issues like mold growth, insulation damage, and wood rot.  At best, closing your vents year round is a gamble.  It may improve the situation if you have no drainage issues, a tall crawlspace and a really good vapor barrier.  The other big issue with this method is that it is a violation of building code.  Building codes are in place for a reason, and there is a reason why this method is not allowed.

If you want to protect against outside humidity you do need to close the vents.  But you need to use one of two methods to meet code.

1)      Encapsulated and Semi-Conditioned Crawlspace.  10 years ago North Carolina changed their building codes to allow for sealed or encapsulated crawlspaces.  By sealing all air entry points and covering the ground and walls with a thick vapor barrier, and encapsulated crawlspace blocks every possible entry point for moisture.  To balance out any small amounts of humidity that seep in, the crawlspace is supplied with some conditioned air.  The point of this air is to balance out the humidity levels.  Conditioned air is low in humidity and thus stabilizes the crawlspace moisture levels just like it does inside your home.

2)      Dehumidifier.  Sealing off your vents and installing a dehumidifier in the crawlspace is another code approved method of keeping the crawlspace dry.  This is a great option if you don’t want to go to the extra effort of a fully encapsulated crawlspace.  If you have a properly sized crawlspace dehumidifier, it will draw out the moisture in the crawlspace.  You can get away with just a simple vapor barrier with this option.  It does improve the energy efficiency of and longevity of the unit to do an encapsulation because it reduces the workload.

Getting the right answer to the question of whether or not to close your vents can have a major impact on your wallet and your health.  An improperly closed crawlspace can have significant un-intended negative impact. 

If your looking to seal your crawlspace and seal it right, contact us for a free evaluation by calling 919-287-7744.