Masonry Magazine April 2007 Page. 48
FLASHING AND DRAINAGE
wall assembly. Proper placement of the air barrier, WRB or a vapor retarder within the wall assembly deserves a long discussion, worthy of its own article.
Installation
THE FINAL STEP to achieving a fully functioning flashing system is ensuring good workmanship during installation. Properly designed and detailed, flashing systems with carefully specified materials still will be subject to poor performance or failure if good workmanship is not provided during installation. The key considerations during installation include the following:
1) Materials must be supplied and installed as specified by the design professional. Use of poor-quality materials cannot be allowed.
2) All seams, joints and corners must be lapped and sealed thoroughly.
3) Full support for flexible flashing must be installed.
4) When using self-adhesive flashing, all surfaces to which the flashing will be adhered must be cleaned and primed. During cold weather, heat guns may be required to ensure proper adhesion.
5) Flashing installation should be sequenced to avoid damage until it is fully protected within the wall cavity. Flashing often is installed in the bed joints of CMU backup materials and left hanging for several months until the exterior brick is installed. This practice leaves the flashing highly susceptible to damage from wind and construction activities, and should be avoided.
6) The wall cavity must be kept clean of mortar and other materials that will bridge the gap between the exterior and interior masonry wythes and clog weeps. Without a clean cavity and clean weeps, the flashing system will not be able to serve its intended purpose.
A quality control program provided by the contractor is essential to ensuring proper installation of flashing systems.
Conclusion
ALTHOUGH FLASHING systems are considered secondary lines of defense against interior water penetration, they are no less important since all masonry walls are susceptible to water entry. Ensuring these systems work properly starts with understanding the limitations of masonry walls and the flow of water, once it breaches the exterior skin of a building. The best practice in detailing flashing systems is to assume the veneer will not be present and the flashing, along with a properly installed WRB, will be the primary line of defense against moisture infiltration.
Joshua J. Summers is a principal structural engineer at Building Technology Consultants, PC. Summers has evaluated and developed repair designs for numerous masonry buliding components. These projects have included both solid-and cavity wall construction with brick, CMU, terra cotta, limestone and clay tile materials.
Kami Farahmandpour is the principal of Building Technology Consultants, PC. His expertise is concentrated in the evaluation and repair of building envelopes, including various types of exterior walls, waterproofing systems and roofs. Among his many professional activities, he is currently serving a three-year term as an associate director of the Sealant, Waterproofing and Restoration (SWR) Institute. He also is the co-author of "A Practical Guide to Weatherproofing of Exterior Walls," which was developed by SWR Institute.
ABOUT SWR INSTITUTE
The Sealant, Waterproofing and Restoration Institute is a non-profit corporation of more than 230 leading commercial contractors, manufacturers and consultants in the sealant, waterproofing and restoration construction industry. Through education and fellowship. SWR Institute elevates the industry's standards of practice and provides a forum for those engaged in the application, design and manufacture of sealant, waterproofing and restoration products. For more information. please visit www.swrionline.org, or call (816) 472-7974.