John Brown, a board member at a small West 53rd Street co-op in Manhattan, recalls a recent roof leak — the kind of mysterious, perhaps pervasive leak where many contractors would suggest an overall roof repair, with all its attendant inconveniences and expense. But one company suggested merely a 10-by-10-foot rubber patch, at a cost of between $1,500 and $2,000. Would that quick-fix solution prove costly in the long run?

"We felt it was a gamble," says Brown, whose board then devised a homemade test. "Since the leakage happened after some heavy rains, we tried to replicate it with a hose up on the roof." That produced no new leaks, and so the board "felt comfortable that the [10-by-10-foot] area was the most likely spot. We went with the roofer's suggestion, and it took care of the problem."

Many times, however, a board needs something more. That's where structural testing comes in.

The Simplest Test

"Stand on the outside of your building on the street and look at the façade," advises Stephen Gottlieb, head architect of the restoration firm Superstructures. "Take your time and use binoculars. You want to look for signs of water movement or cracks."

If your façade has some dirt or is slightly grayed from day-to-day wear, look for an area that's clean. If you see such an area around a drainpipe, says Gottlieb, that could mean "that water instead of coming down the pipe is bypassing it and coming down the wall. The pipe may be blocked."

Another quick and easy test Gottlieb suggests is to look for "any areas where there's white or gray crust on the wall. The white stuff is usually shiny and sparkly, and that's salt," which typically exists within both bricks and mortar. When leaks or environmental changes bring water through either, it leaves a salt residue called "efflorescence" on the outside. If, on the other hand, the residue is a gray, scaly patch, that means carbonate crust is leaking out of the mortar. Either way, it's "often a sign of water movement through the wall, and someone should look behind it or above it." While bricks and mortar are porous and designed to handle a certain amount of moisture, enough of it will eventually weaken them.

After the walls, check the roof. Have plastic bags blown in and blocked a drain? Has someone stuck a beach umbrella through the roof, or used a chair with pointed legs? Workers often drop nails — and if someone steps on one, it can poke a hole in the rooftop material that will allow in water during rainfall. That may seem trivial until you consider the "Grand Canyon Effect" on a smaller scale.