Exterior wall coverings, along with the roofing, flashings, windows and doors, are designed to provide a weather-resistive barrier that separates the interior of the structure from the elements. Low maintenance and attractive appearance are just two reasons why hardcoat stucco has become so popular over the years. At the same time, the building industry has become aware of the need to protect the exterior wall sheathing from moisture damage.

The walls shall be constructed so that water does not accumulate within the assembly. This means creating a water-resistive plane behind the exterior veneer that allows moisture that does get through the exterior cladding to drain down and out without coming in contact with the wood framing. Detailing around windows, doors and other penetrations in the envelope is equally important in protecting the wood frame structure behind the stucco from being damaged by water infiltration.

Since the wall sheathing behind the stucco is the lateral load resisting system of the structure in addition to the supporting surface for the exterior siding, it is important to see that continuous undetected penetrations of the siding by moisture do not create structural damage such as decay and corrosion or environmental damage which may cause health related problems such as the growth of mold and mildew. To this end, the removal of moisture that gets past the exterior cladding before it contacts the wood framing is the primary goal of the weather-resistive barrier and why it is critical that it be installed properly. This barrier is technically termed the secondary drainage plane.

This document is designed to provide guidelines for the application of stucco exterior finishes in the greater Johnson County area and is intended to parallel the task force that developed the Stucco Best Practices Report.