What is Moisture Capillary Transfer?

Capillary action refers to the ability of water to travel up against the pull of gravity through a porous material. One common example of this action is water “wicking” up through a paper towel, following the direction of the paper fibers. Although not as serious as bulk water movement, capillary forces are both powerful and rather secretive, since they often work in the dark of a crawlspace, causing significant damage to a building without the occupant’s knowledge.
Capillary action can best be controlled by providing a capillary “break” such as plastic, metal, damp-proofing compound or another impermeable material, or by leaving air spaces that are too large for capillarity to occur.