Facilities Check List
Practical, step-by-step guides for the busy FM
September 2000
Ways To Deal With Water Intrusion
Of the primary factors contributing to premature building decay, most originate with people: design deficiencies, improper construction, neglected maintenance, etc. The remainder are products of nature: air (especially the oxygen in it), temperature (in extremes and fluctuation), wind (with its pressure and suction), and water. The most important of these is water.
Six forces that cause water intrusion into a building are listed below, along with the means to control each.
Force 1: Gravity
Solution: Sloped joints use gravity to shed water to the exterior at vulnerable points, such as a horizontal joint between two wall panels.
Force 2: Kinetic Energy
Solution: The force of kinetic energy, as in wind-driven rain, is more difficult to control. An internal baffle blocks the wind-driven rain and allows the water to exit to the outer wall face.
Force 3: Surface Tension
Solution: Surface tension allows water to move horizontally along a flat surface facing downward. A drip is a groove that breaks the surface tension and causes the water drops to fall.
Force 4: Capillary Action
Solution: Capillary action draws water into a narrow opening. A capillary break is an opening wide enough to prevent the action of this force.
Forces 5 & 6: Air Currents and Pressure Drops
Solution: Air currents can carry water into the wall system through its joints, or water and air can be sucked in if the pressure within the wall is lower than the pressure on the outside.
Water that penetrates the outer seals of a building envelope is drained back to the exterior through holes or tubes called the weep system. A weep system must be designed so that the weep holes do not allow wind-driven rain to enter and do not draw in rain-laden air when a pressure difference occurs.
The best method of controlling the forces of air currents and pressure drops is the pressure-equalization chamber, an opening that allows the air within the wall to rapidly mix with outer air so that no pressure difference can develop. This is called a rain-screen wall because it prevents the suction of rain-laden air into the wall system.
This installment of FM Check List is adapted from BOMI Institute’s Design, Operation, and Maintenance of Building Systems, Part I, course, (www.bomi-edu.org/19011.html), a required course in BOMI Institute’s Real Property Administration (RPA) and Facilities Management Administrator (FMA) programs.
