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Crawl Space Humidity

Crawl space humidity is a major problem in homes across the world.  Humidity leads to an unhealthy crawl space (which means an unhealthy home) and a rotting, damaged structure supporting your home.  However, the principal sources of crawl space humidity— namely crawl space vents, flooding in crawl spaces, and water vapor passing in through the concrete and dirt crawl space walls— are all possible to control with some simple solutions.  With a simple crawl space upgrade, your home can become healthier, more comfortable, and much more energy-efficient.

The “Stack Effect”

Crawl Space Humidity Stack EffectWhen crawl spaces have open vents, the air that flows into the space does not pass through the crawl space in out the other vents.  Instead, a large portion of the air will flow upwards through the floorboards (and insulation) and enter your home.

The reason is this:  as the air in your home heats, it naturally rises upwards, eventually passing out of the house through the attic or upper levels.  As this happens, all the air in the house will naturally shift upwards to fill in the space left by the departing air.  This means that new air must move into the home below.  If you have a vented crawl space, some of this air will be pulled from that space.

So the crawl space vents aren’t doing their job of creating air circulation through the crawl space.  What are they doing instead?  Adding humidity to the crawl space in the summer and cooling the crawl space in the winter.

Crawl Space Vents

Crawl Space Vent ProductIn the winter, cold air flows into the crawl space vents and upwards into your home.  Unfortunately, the crawl space is there for a reason, and there are many things in the space that you really don’t need cold.  If you have a furnace, heating ducts, hot water pipes or a water heater in the crawl space, you’ll be spending more on utility bills as these objects fight to beat back the cold. 

After everything in the crawl space is cooled, the cold will them move upwards and seep through your flood boards (the cold air is rising because of the stack effect).  If you have insulation on your crawl space ceiling, this will help for a little while, but the summer heat and humidity will ruin it within a few years (more on that soon).  As the cold air moves through the floorboards, it makes for a cold, uncomfortable flooring, and

Crawl Space Mold and RottingIn the summer, hot, humid summer air will pour into the crawl space continuously.  As this hot air enters your crawl space, it will quickly cool underground.  As this humid air cools, it will lose much of its ability to hold moisture, and this extra water will be dropped on all surfaces in the area as condensation.

And after the crawl space is soaked with moisture and humidity, the air will (again) move upwards into your home.  And because air conditioners spend much of their energy on dehumidification, it’s much harder to cool humid air than when it’s dry.  As it adds humidity to the air (as well as odors, mold spore allergens, dust mite waste allergens, formaldehyde from fiberglass resins, and other pollutants), your air conditioning bills will rise dramatically.

In the end, crawl space vents have nothing to offer.  They add heat and humidity in the summer and cold air in the winter, all of which adds your home.  And even worse, as the humidity fills the crawl space, you can expect a wide variety of new long-term problems like mold, rot, dust mites, termites, rodents, carpenter ants, and the eventual need to hire a contractor to crawl into this narrow space, rip out the disgusting rotting wood, and replace it in cramped quarters.  All of these things combine to mean bad things for your health and pocketbook!

Click here to read more about mold, pests, and allergens and how they affect your crawl space and home

Click here to learn about crawl space vent covers, crawl space vapor barriers, and dehumidifiers