Conditioned Crawlspace

Crawlspaces are fundamentally a bad idea, the way they are currently constructed. In the old days, log cabins were built on piers with a pretty much open crawlspace. Now we almost close them, instal plumbing and air conditioning ducts, and trap the moisture inside. So what do we do with a crawlspace?

A quote from Bruce Lee comes to mind, “No way is THE way”. There are many solutions, depending on your budget, your environmental goals, and the unique conditions in your crawlspace. Sometimes installing a high quality vapor barrier will solve the problem. Sometimes installing powered foundation vents will solve the problem. Sometimes it takes powered foundation vents but the intake air must be conditioned as it enters the crawlspace. Sometimes powered foundation vents are installed with the make-up air coming from the living space air via a hole in the floor.

A closed system is the most controllable environment. A closed crawlspace system includes all solutions which have closed or non-existent foundation vents. The ground in most crawlspaces will allow some humidity and earth gases unless it is sealed in a vapor-proof manner. This includes water proof seams, a mechanically fastened wall and pier membrane, and a floor membrane which has a low enough permeance rating to prevent radon and other earth gases from penetrating. If a high water table is a possibility, a sump pump, positive drain and a french and/or field drain should be installed.

A word about a recent variation on conditioned crawlspaces. Sometimes the crawlspace is closed, a high quality vapor barrier is installed, and the supply duct has a dryer vent flapper installed on the HVAC system to blow into the crawlspace and positively pressurize the crawlspace. Seems like a good idea at first, but there are some potential problems. Nature seeks an equilibrium. Where is the area of least resistance to air pressure and radon gases when you positively pressurize a crawlspace? Could it be the dryer vent flapper in the air ducts, which introduces the crawlspace air to the lungs of your home or building. Hmmm.? Something to consider.

So, to make a short story long, the absolutely most controlled and reliable crawlspace solution is to seal the foundation vents, install a high quality, low-permeance vapor barrier, and install a dehumidifier. This makes the crawlspace a semi-interior space, seals out the earth gases, and maintains a pressure-neutral condition. The downside is, a commercial dehumidifier is expensive, and expensive to operate. This option is also dependent on sophisticated equipment. And one thing you can count on is, equipment will eventually break. So, like any equipment, it must be monitored and inspected semi-annually, or at least annually.

To schedule an inspection and get an estimate which matches your budget, goals and specific situation, call 615-371-5355.