To most architects, the opportunity to conceive and design the renovation or adaptive reuse of an existing building is seductive. Once the perfect image and plan layout is conceived, the temptation to dive into project documentation is great. However, more often than not, a little “exploratory surgery” is necessary.Old buildings are fraught with the potential for concealed architectural surprises. Sometimes, just as with live patients, certain “symptoms” provide clues to more sinister hidden problems. A few common issues are:
- Bulging brick with chalky-white efflorescence and crumbling mortar can conceal years of deterioration of embedded structural-steel members caused by continuous water penetration into a wall.
- Brown water marks or bubbling paint on a plaster ceiling could be from an easy-to-fix pipe leak just above the ceiling or a concealed rainwater conduit. In one of my projects, the Joseph R. Biden Railroad Station in Wilmington, Del., a well-meaning plumber had skillfully, but inaccessibly, placed a rainwater conduit behind a lined terra-cotta cornice in 1907.
- Parged stone rubble walls may conceal decayed lime-sand-water that has since turned back to its primary element: sand. If this is the case, tapping on the parging will sound hollow, signaling that a significant repointing project will be required.
Despite these three commonly visible existing building issues, more often than not, the most serious and costly problems are completely concealed behind layers of “improvements” or previous renovations or additions. A recent waterproofing scenario experienced by my firm is an example of how preliminary testing of an existing structure may deflect attention away from an obvious solution and cause the team to chase a phantom culprit.
In the Joseph R. Biden Railroad Station restoration and renovation project, the tracks ran over the station’s main concourse—not below it, as is the case in most 20th century stations. The project entailed the replacement of waterproofing membrane installed during a previous renovation between the track and the concrete base slats to which the rails are affixed and which form the roof of the concourse. In this instance, thermal imaging of the existing track bed revealed water had, indeed, penetrated the waterproofing system installed in a previous renovation.
Unfortunately, the original track bed/concourse roof structure consisted of a multiplex system of 12-inch-wide riveted steel plates forming a corrugated bridge-like structure that was believed to be filled with coal cinder covered with several inches of cast-in-place concrete. The existing waterproofing system was removed; the cast-in-place slab was cleaned; and a new liquid-applied roofing/waterproofing system was applied. Despite this improvement, the spaces below the track bed continued to leak sporadically.