Watch the video on How Moisture Moves.
Water intrusion compromises the quality of a home and reduces its market value. Water can enter a home in many ways. Good water management strategies both combat and cooperate with physical forces to allow water to drain or dry. Planning for drainage and drying, rather than assuming that it's possible to keep things dry, is an excellent step in preventing moisture damage. In order to plan for drainage and drying, it's important to understand the different ways moisture can get into a home.
Gravity
Gravity moves water down the surfaces of a home. Water moving under the force of gravity always takes the path of least resistance. If water is given a path toward the home, it will leak into the interior through openings, seams, or gaps between materials.
Wind
Wind is a strong force that can push moisture across horizontal surfaces and even make it defy gravity. Wind can drive moisture up valleys, into ridge vents, and behind exterior finishes. The exterior finish alone isn't enough protection to prevent wind-driven rain from wetting the sheathing and framing.
Adhesion
Adhesion is water's ability to cling to surfaces. Water can cling to the underside of an eave or window sill. It can also find its way to the underside of soffits, where it can wet and eventually rot the sheathing and find its way into the interior of the home. Over time, it can also be absorbed by the materials it's wetting, such as wood trim and sheathing.
Capillary action
Capillary action is the wicking of water into a porous material via adhesion and surface tension. Water can wick into concrete, brick, wood, and any other porous materials. Water wicking through a foundation footing or slab is a good example of capillary action at work. The problem can show up as damp carpeting on a slab floor or as dampness around the base of the foundation wall.
Hydrostatic pressure
Hydrostatic pressure is the pressure that standing water exerts on a nearby surface. An example of hydrostatic pressure at work is the force water exerts on a foundation wall. The soil below grade contains water, and if the amount of water below grade builds up to a certain point, the water-saturated soil puts a large amount of pressure on foundation walls. This pressure can force groundwater into a basement or crawlspace through cracks or holes in the foundation walls. Efflorescence and peeling paint are visual indicators of hydrostatic pressure forcing water into the interior.
There are different strategies available to combat and cooperate with each of the ways moisture moves. For instance, to relieve hydrostatic pressure at the foundation, you can install a drainage board as part of the foundation's waterproofing system. Water will form droplets inside the small tunnels in the drainage board material, and then seep downward through the board instead of moving toward the foundation walls. It's important to understand how water can get into a home to develop good water management strategies.
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