Originally published in Interiors & Sources

04/01/2013

Why Do Flashings Fail?

Causes and solutions for parapet problems

By Richard L. Fricklas

 
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    NRCA now offers illustrations showing base flashings applied to a curb that’s fastened to the deck. This strategy eliminates differential movement, but a counterflashing (usually metal) is necessary to cover the flashed curb.

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    Diagonal wrinkles and the consequential tearing of flashing materials signal an imminent leak. Flashings are responsible for roughly 95% of all roof leaks, so it pays to understand why.

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    Parapets are a common cause of building headaches, but are required by code in many places.

Have you spotted diagonal wrinkles or tearing in your roof base flashings? This vital waterproofing component is responsible for roughly 95% of all roof leaks, but little attention is paid to the reasons why.

The Limitations of Roofing Resources

Richard (Dick) L. Fricklas was technical director emeritus of the Roofing Industry Educational Institute prior to his retirement. He is co-author of The Manual of Low Slope Roofing Systems, and continues to participate in seminars for the University of Wisconsin and RCI Inc.-The Institute of Roofing, Waterproofing, and Building Envelope Professionals. His honors include the Outstanding Educator Award from RCI, the William C. Cullen Award and Walter C. Voss Award from ASTM, the J. A. Piper Award from NRCA, and the James Q. McCawley Award from the MRCA. Dick holds honorary memberships in both ASTM and RCI Inc.

Reams have been written about flashing materials, especially with the new MB and single ply systems available now. However, you may not have the original construction details, which can throw a wrench into the problem-solving process. These details were probably provided by licensed architects and engineers originally, but they may not be available when it’s time to re-roof or re-cover. Those two tasks account for about two-thirds of low-slope roofing activity, so without the original details, you’ll need to deduce the problem and solution with other resources.

For example, material manufacturers and roofing trade associations such as the National Roofing Contractors Association (NRCA) will furnish generic details for roof base flashings, but retrofitting vertical walls, parapets, and copings is usually beyond their scope of work.

Building owners often rely upon the roofing contractor to furnish drawings of the roof-to-wall configurations that will be discovered under the scope of work, but contractors generally do not have the license to prove to a code official that their drawings will meet the current codes.

What Causes Flashings to Wrinkle
Climate is a major player in flashing issues. Significantly more attention is focused on energy considerations now than it was just a few years ago. This means that thicker thermal insulations may be specified, as well as air barriers to reduce air leakage and consequential condensation problems.

Those same seasonal climatic fluctuations are also responsible for temperature-related differential movement in the parapet wall above the roof, which is alternately subjected to freezing and baking temperatures on both sides that cause dimensional changes. The wall above the roof, too, not being a load-bearing wall, is usually not as substantial as the walls below the roof.


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