Concrete Block Walls - concrete blocks are the most common crawlspace foundation type used today. They are hollow and very porous.
Cinder Block Walls - Cinder block is a type of concrete block made with the uncombusted remains of coal fires. Because these blocks are made from the available and lightweight cinders (from these fires) they are extremely porous and leaky. Cinder blocks have not been manufactured for about 50 years now.
Why are concrete blocks used if they are so porous? Block walls are the easiest AND cheapest material to build a foundation with. Unfortunately, they are the least resistant to water and air. Not only do water and air come through the cracks between the blocks, but they also seep in though each block's hollow cavities. Block walls are referred to as ‘God's gift to waterproofing contractors' because of all of the water problems they cause for homeowners.
Other Types of Crawlspace Foundations Used
Poured Concrete Walls- basically these walls are solid concrete. These types of walls are found in newer homes and often do not allow water or air to penetrate them.
Stone Walls - these walls are found in numerous older homes. They are also extremely susceptible to leak air and water.
Brick Walls - from time to time AquaGuard will inspect a crawlspace with brick walls. This is rare though.