The construction industry recognizes more and more that the building envelope is a fully integrated and interrelated assembly of systems. As such, I feel the need to discuss the importance of water resistance and structural integrity in existing wall surfaces, which are adjacent and connected to your project’s new (replacement) roof system. The focus of this article is not how to design a replacement roof system but how to address adjacent masonry to ensure it doesn’t work against the success of the new roof.These principles actually apply to any wall system that connects, generally above and adjacent, to your roof, but masonry poses some distinct concerns. Water intrusion, thermal movement and structural integrity of this masonry, along with locations of embedded flashing, all come into play as the new roof system is properly integrated into the adjacent rising wall, parapet wall or even perimeter edge wall beneath the roof.
COMMON MASONRY ISSUES
Thomas W. Hutchinson, AIA, FRCI, RRC, a roofing forensics expert, has said, “long-term service life is the true essence of sustainability”. Moreover, designers specify (for owners to buy) warranties of 20, 25 years or more with new roof systems. It’s just good common sense that you can’t allow a new roof to be jeopardized by water intrusion from an adjacent system because of an oversight in the original analysis of the situation.
Many of us have been called by an owner who says his or her new roof is leaking, only to find roof-mounted equipment or an unrelated system is actually leaking. However, if the leak is stemming from another aspect of the building envelope, such as an adjacent parapet or rising wall, which is now jeopardizing the investment made on a new roof, that you (the designer) should have foreseen, it makes for a very difficult position. The roofing system manufacturer, who holds the warranty, and the owner are going to look at you as being responsible.
Let’s examine three common occurrences using actual case studies. All three situations, which occurred on schools in the Northeast, exemplify the condition of adjacent masonry was deficient and had to be corrected, adding a significant degree of scope and cost to the project to guarantee a roof design that would perform over the long haul. These three cases cover:
1. Repairing the masonry and covering it.
2. Altering the masonry to change the location of embedded flashings.
3. Replacing structurally unsound/failed masonry with another material.
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