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Unvented Crawlspace

Posted: May 18, 2017

Many homes here in the gulf south have foundations that are raised and have semi-enclosed crawlspaces. The foundation walls often sport rectangular or decorative cast iron vents, spaced evenly around the perimeter of the house. However, if you are one of the many homeowners who have one of these raised homes with a crawlspace, do you dream of spending loads of time under your home?  Probably not! This question likely conjures up visions of creepy spiders, puddles of god-knows-what, muddy earth, and the damp smell of mildew. The thought of having to crawl under your home for any reason might be cringe-worthy. Nasty, grimy crawlspaces are NOT healthy for you OR your home… but it doesn’t have to be this way!

Why vented crawlspaces don’t make sense

The humidity in southeast Louisiana leaves us “sticky” to say the least. Ventilating a crawlspace with wet air in order to make a crawlspace dry makes no logical sense at all….yet many homes are constructed with foundation vents and fiberglass insulation installed on the underside of the subfloor. The crawlspace ventilation is restricted by fencing, neighboring homes, or landscaping. Some even have the clothes dryer exhaust ducting dumping lots of moisture within the crawlspace or landscape irrigation spraying water underneath the home. I have even pounding of rain water underneath raised homes. These conditions are a recipe for a (moldy, termite-filled, wood decay) disaster. The only way to dry a problem crawlspace in the gulf south is to mechanically dry it with a dehumidifier.

How to clean up your crawlspace

Let me introduce you to the concept of an “unvented, semi-conditioned” crawlspace. This is a clean, dry space where drooping fiberglass batts have no place, organic growth is banished, and the hardwood floors above lie down flat like exhausted toddlers at nap time. You may think that in our hot-humid climate, this tidy, healthy crawlspace is an impossibility. It is not.

An “unvented, semi-conditioned” crawlspace is just that….a crawlspace where the foundation vents are covered and sealed up and the (previously moist) air is being dehumidified. Without excess moisture, organic growth cannot grow, building materials do not decay and termites are less likely to make a home there. Also, the moisture that used to be in the crawlspace (convincing the hardwood floors to curl up at the ends) is no longer there. Hooray! Are you sitting on the edge of your chair, just waiting for step-by-step instructions on how to implement this?

Wait no further:

  1. Make certain all bulk water sources are pointed AWAY from the crawlspace (irrigation sprinklers, downspouts, etc.)
  2. Drain rainwater away from the foundation. You may need to raise the level of dirt underneath your home higher to prevent ponding of water.
  3. Create a moisture barrier at the ground level. The moisture barrier should be created by covering the entire ground in the crawl space with 10 mil cross hatch or 14 mil polyethylene covering. Install the ground cover up to the bottom edges of the foundation wall and interior piers. Overlap the joints 12”.
  4. Close off the perimeter of the house at the crawlspace openings with Extruded Polystyrene foam board or similar materials. The outward face of the foam board can be painted black to imitate the darkness underneath the home at any exposed locations.
  5. Add a properly sized dehumidifier in the crawlspace that addresses the entire crawlspace of the home. This will control moisture levels inside the newly created unvented crawlspace with electronic controls located in the living space set to 50% relative humidity. 

If this is something you’d like to consider and hire out, call Energy and Comfort Solutions to have the ground cover and dehumidifier installed. Their contact information can be found on our site here: http://bit.ly/EnergyComfortSolutions? 

Enjoy the peace of mind knowing you have a dry, clean space below your home. Your subfloor will thank you!

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