Building codes for dirt crawlspaces allow for the space to include vents - the truth - they require them to be vented. Even though these codes are stated and must be followed by builders, there are some exceptions.
Unfortunately, these exceptions are extremely hard to understand, but at least it shows that some builders know that vents are not a necessity in crawlspaces.
AquaGuard's dealer network, Basement Systems, believes that code writers should act now and change the code to disallow exposed earth under a house and forbid venting in crawlspaces. Our dealer network hired an engineer who specializes in moisture and energy issues to do an assessment on an encapsulated crawlspace- just to prove that it would [and should] pass home inspections…even with sealed vents and covered dirt floors.
The engineer measured the relative humidity and wood moisture content and discovered them to be much less than the average conditions in vented, dirt crawlspaces. He stated in a report that a fully encapsulated crawlspace with sealed vents is "providing a durable, high-performance foundation system…that will outperform a vented crawlspace."
So why would you not want to encapsulate your crawlspace?