Using Sealants as a Stop-Gap for Water Intrusion

Posted on 7/25/2013 1:46:32 PM By Bob Braun

In my last post, I began digging deeper into the subject of water intrusion into building walls.  I looked at several classic water intrusion failures and reviewed how the public and building industry responded.

In this post, I'll review a very common and specific water intrusion issue for windows as related to the use of sealants.  We will also consider how building design changes and new standards over the last 20 years have contributed to successes as well as failures.

First, let’s look at the window-wall interface and fairly recent innovations in window construction.  Historically, most residential windows were set well into the window opening back from the exterior façade.  A sloping window sill then directed rain water to the exterior surface and helped prevent water intrusion into the building.  The photo on the left below shows this configuration and the one on the right a newer replacement window design.  New construction finned windows as well are often set into the opening in a similar way to the replacement window.


 historic window, water intrusion

 window, water intrusion, windows and water intrusion, sealing windows

 Historic Window Design  New Replacement Window Design

The replacement window design, with the projection beyond the wall surface, has a much greater dependence on an effectively installed sealant to prevent water intrusion.  Flashing is normally not employed in the replacement window configuration since this type of window is set into the old window frame after the operable window is removed.  Weathering and excessive movement of siding relative to the window movement, caused by thermo cycling for example, can cause the sealant joint to fail.  Often this joint is installed in a fillet bead manner without backer rod, thus creating an even greater challenge for the sealant joint.  For this and similar designs to work, the proper installation techniques and the appropriate sealant must be used.  Using a sealant with high movement capability and excellent weathering characteristics is very desirable. Longer term, the inspection and maintenance of the joint is critical as well.

Another residential building design feature that accelerated in the period from 1980 to the present is the increase in two or more story houses, townhouses, and condos.  Post 1945 houses tended to be mostly one story, and thus included a roof overhang that protected the head of the window from rain.  The first floor of a multi story building would not have this protection from rain.

The reader should find the paper titled “Water Intrusion in Central Florida Homes During Hurricane Jeanne in September 2004” of special interest.  This paper focuses on the many newer Florida houses that experienced water intrusion.  (I myself owned a circa 1945 stucco clad building located in an extreme weather location in central Florida and it did not experience water intrusion.)  This paper, published by the University of Central Florida (UCF) Housing Constructability Lab in August 2006, did not find a correlation to water intrusion and the number of stories; however, I suspect that the high intensity of the wind driven rain from the east largely negated the protection effect of the roof overhang.

This study’s “Analysis of Findings” section highlights the importance of sealing: “A follow-up inspection of these homes found a variety of possible causes including: poorly sealed windows, unsealed wall penetrations (dryer vents, plumbing, electrical, rain gauge, etc.), poorly sealed expansion joints, and numerous cracks of varying shapes and sizes. Findings from an earlier inspection study confirmed the prevalence of these issues throughout the central Florida new home market.”

Now what has happened more recently in standards development?  In several of my early posts, I reviewed most of the test methods for evaluating water intrusion.  The UCF paper also details theASTM Test Method C1601 Standard Test Method for Field Determination of Water Penetration of Masonry Wall Surfaces.  In addition to the many other water intrusion tests already discussed, the completion of ASTM E2112 - 07 Standard Practice for Installation of Exterior Windows, Doors and Skylights was a major accomplishment because it brought together many of the best minds in the window related industry to provide best practices information to the window installation industry.  E2112 will need revision soon once again since ASTM requires that all standards be revised or reapproved as-is every five years, excluding the maximum three year grace period. 

In my next post, I will continue to review details of water intrusion into walls from the standpoint of recent standards and innovations in self-adhered flashings and liquid applied seals.  

comments powered by Disqus