Water, Water, Everywhere

High and low. We had a job at a co-op in Queens where there was water leaking from the building’s roof into four penthouse apartments and through the foundation walls into the building’s basement. The roof leak had been going on for six months, and the residents were basically just putting up with it whenever it rained, moving their furniture around and setting out buckets on the floor. As structural engineers, we were much more concerned with the basement because that can lead to concrete slab failures and extremely expensive retrofitting repairs. There’s a sense of urgency, so we wanted to check that out right away.

The water that was infiltrating into the basement had a high salinity level and had corroded the rebar in the concrete and was encroaching onto the boilers and some of the electrical connections down there. This building is located deep in Queens and not anywhere near water, but what people don’t realize is that you can have groundwater that’s high in salinity and sulfur even if your building isn’t close to a river or ocean. Pretty much all of the water that’s underground right now has a highly corrosive potential.

Point of origin. The challenge was finding the source of the basement leaks and exactly where the groundwater was coming in. When you see water coming in through the walls, the source can be 5 feet away or 20 feet away, and in some really crazy scenarios it’s coming in from several floors away. Using thermography, we set up small remote monitors on-site and collect data over a couple of weeks to trace the water to its source. The monitors use a combination of infrared wide-angle lenses to sweep the area. We also check for changes in humidity and temperature in the environment with onboard sensors. They’re small and discreet and you can stick them on anything — pipes, boilers, ceilings, underneath floorboards. Whenever we visit a site we show up with maybe 10 monitors and put them where they’re needed.

The big picture. The monitors give us photos, but what we’re really getting are two-dimensional arrays of numbers that tell us where the moisture and salinity are present. And these numbers are being collected about 60 times a second. We run through the arrays to try to find a pattern on how the water is getting in. 

At this building, there were a few different ingress points in the basement, none of which were obvious if you were looking with just your eyes or feeling the wall, and it ended up not being that difficult of a repair job — just applying sealant seams in a few specific spots. Still, you needed to know exactly where to do that. If you had guessed blindly and applied a rubber sealant across the whole wall, it wouldn’t have solved the issue because there was actual pitting behind the concrete wall face that needed to be filled.  

Top job. As for the roof, there was a rubber membrane that had been ripped in a few spots, and the patch repairs took just a few days. The co-op was lucky, especially since it waited half a year before calling us in. If you see or suspect a leak problem, you want to catch it as soon as possible. For most buildings, we can do a simple roof or basement survey for about $5,000. If we suspect something serious, we also have radar capability and impact testing to determine a building’s structural integrity. In this case, the concrete and rebar in the basement were fine. But if the building manager had not mentioned the leak and another six months had gone by, it would have been terrible.