When you mention forensic investigations, many people think of television detectives and crime labs. Fair enough, but whether the subject is a homicide or a building failure, the fundamental aspect of a forensic investigation is not the often obvious result (a person is dead, or a building collapsed) but is the careful examination of physical evidence and the use of logic to determine the how and why. That’s exactly what Vitruvius did in portions of Books II and VII of De Architectura (his “Ten Books on Architecture”). He attempted to diagnose how and why something failed and, furthermore, what to learn from that when designing new buildings so as to avoid similar failures.
The forensic investigations of Vitruvius are similar to a large part of what I do here at Simpson Gumpertz & Heger (SGH). As a result, at various times, I’ve realized a very direct parallel between my technical observations and conclusions and those of Vitruvius in his famous treatise. It’s both inspirational and humbling to think you’ve figured something out yourself and then realize that someone else had already figured it out over 2,000 years earlier! It’s kind of like having a really cool grandfather who always inspires you but who always knows more than you do, no matter how much you learn.
The first time I realized a parallel between my forensic investigations and those of Vitruvius was in the late 1990s, when I was only a few years out of school and into practice. I was investigating severe, persistent blistering of interior painted plaster finishes in the Old State House (1748) in Boston.
What puzzled people for a long time was that the severe damage to the interior paint and plaster occurred only in the northeast corner of the building, yet the exterior brick walls, the flashing and the slate roofing at that corner looked just as good and just as tight as on the rest of the building. Further, over the years, multiple attempts at repointing the brick and improving the flashings and roofing at the problematic northeast corner had failed to halt the interior problems.
After investigating the problem, my colleagues at SGH and I found that the interior blistering and damage were due to a combination of factors that coincide at the northeast corner. One of these factors was that the building was largely shielded by taller surrounding buildings, except near the northeast corner, where the exposure is wide open to wind-driven rain from the northeast. (“Nor’easter” storms are common in Boston, particularly in the winter when exterior walls tend to dry to the interior.)
Another prominent factor was that the interior finishes in the west half of the building, which had no damage, were constructed on wood furring, creating an air space and capillary break between the plaster and the exterior brick masonry walls that made the interior finishes in the west half highly tolerant of moisture in the walls. On the other hand, the walls in the east half of the building, which suffered persistent damage, were constructed with the plaster adhered directly to the exterior brick masonry. This lack of a capillary break and air space made the plaster in the east half of the building unforgiving and intolerant of incidental moisture in the brick walls, which then became inevitable.
In our report, we recommended installing the replacement plaster at the badly damaged northeast corner in the manner in which the plaster in the west half of the building was installed: over furring so as to create an air space and capillary break between the plaster and the brick and thus make the plaster more tolerant of the inevitable moisture in the old brick walls. Fortunately, the direct-adhered plaster in the northeast corner of the Old State House was so thick that it allowed room for creating an air space behind, while maintaining the interior plane of the plaster and its relationship to the wood trim.
In our report, I quoted Vitruvius, who had learned the same durability lesson and made similar recommendations in Book VII, Chapter IV (“On Stucco Work in Damp Place. . .”) for preventing damage to interior plaster by constructing a vented air space between interior plaster and frequently damp exterior walls.
Just a few years ago (about a decade after our original investigation and report), the work was undertaken by the National Park Service in conjunction with a major rehabilitation designed by Tellalian Associates Architects and Planners and constructed by the Lee Kennedy Company. I was pleased to hear from colleagues at Tellalian and Lee Kennedy that our early investigation report was well read and much appreciated, and they had accepted and successfully implemented our recommendation of creating an air space between the plaster and the brick at the northeast corner. Thanks to their good work, the interior plaster and paint at the northeast corner have finally stopped misbehaving.
In both cases (the Old State House and the advice provided by Vitruvius in Book VII), it was prudent to admit and simply accept that the walls would often be damp and install the plaster in such a way that it would be tolerant of the dampness. This very specific example also illustrates a much broader principle of designing for durability: Accept the inevitable, and design in a manner to accommodate it.
More on that in my next blog.