A crawl space with a concrete floor either with or without foundation vents
This type of crawl space is not as common but has its advantages. For one, this type of construction is more energy efficient than an open crawl space if constructed without foundation vents.
The concrete crawl space uses mainly two different types of ventilation:
Ventilation using the forced air (furnace) system of the home
Durable storage option
Although most crawl spaces are too short for this option after the home is built, it offers a lasting means for durable storage.
A bit more costly
Gaining the durable storage does come with a price, usually adding several thousand dollars to the construction costs.
A cap on the odor
A crawl space with a concrete floor has far fewer odor problems than an open crawl space.
Some are constructed with foundation vents
Most are poured as a “mud pad”. A mud pad is a rough poured concrete slab that’s sole purpose is to cap the earth under it- usually without a vapor barrier between the concrete and the earth. Therefore, there is little to no protection for the crawl space against moisture penetration through the (non vapor barrier) floor and the walls.
If conditions change and a water problem shows up it can be very expensive to install a drain system in an existing concrete floor crawl space due to the height.
When installing a concrete floor in a crawl space after the home is built will cause very high moisture in the crawl space due to the drying and curing process. This will go away, but will need to me managed to prevent any new issues.