Keeping Water Out of the House

Water is a major cause of damage to houses. Building components that get wet and stay wet deteriorate and are prone to mold infestation. Homes built before the 1970s were more forgiving of occasional wetting because small amounts of water could dry before causing damage. Homes built since the 1970s may be tighter and more energy efficient, thus, water may stay on components longer and cause more damage. Homes built since 2000 are likely to be even tighter and less forgiving. Keeping water out of homes is increasingly important, and so is inspecting for properly installed and maintained flashing and sealants.

The function of flashing is to create an effective, long term, and maintenance-free barrier against water infiltration into the home. This distinguishes flashing from sealants such as caulk and roofing cement. Sealants require periodic replacement whereas properly installed flashing should function for a long time without replacement. Sealants installed in place of flashing and sealants used to repair flashing are a reportable defect.

We now know that flashing and sealants do not create a perfect barrier against water infiltration. Newer homes are supposed to be designed with a drainage system that assumes water will find its way past flashing, sealants, and other barriers. This is why flashing and sealants should be installed in conjunction with a water-resistive barrier that covers the protected area and creates a drainage plane. Water that finds its way behind the flashing or sealants should drain down the flashing and the water-resistive barrier and out through weep holes or other outlets.

Flashing should be installed, when practical, wherever an opening exists where water could enter the home. Flashing should also be installed wherever trim or other material projects from a wall. A sealant may be installed where flashing is not practical. Wall penetration flashing should be installed at doors and windows, where different wall covering materials meet, at horizontal seams in some wall covering materials such as panel siding, and where vents and exhaust ducts penetrate a wall. Roof penetration flashing is installed where components such as plumbing vents, electrical cables, HVAC vents, and exhaust ducts penetrate the roof. Flashing is also installed around roof penetrations such as skylights. Sidewall and headwall flashing is installed where a vertical sidewall intersects a roof. This occurs at locations such as chimneys, at second story walls above first story roofs, and above bay windows. Valley flashing is installed on the roof where two descending slope roofs intersect. Roof flashing is discussed in the Roof Coverings chapter.