Other simple observational tests include examining the parapet , (the small wall that surrounds and sticks up above the roof) and the coping (the top pieces of stone on a parapet wall). "Make sure the joints are tight," Gottlieb says. You should also check for cracks at the building covers and above the windows, where the "flashing" — a piece of plastic or other material that channels water from inside the wall to the outside — may be broken, improperly installed or blocked, trapping water in a freeze-thaw cycle that can crack the wall and corrode any steelwork there.

Destructive and Non-Destructive Testing

All these things are akin to the physical exam a doctor gives you during a checkup before ordering any advanced tests. So when structural tests are called for in a building, what are the brick-and-mortar equivalents of x-rays and MRIs?

There are two major kinds of tests, says architect Joakim Aspegren, president of Architecture Restoration Conservation: destructive and non-destructive. The former isn't as bad as it sounds. "A typical example," he notes, "is a masonry probe, which involves removing one or two wythes [i.e., a continuous vertical section of masonry one unit in thickness] of brick, and is typically done to evaluate the underlying condition.

Another type involves taking a piece of masonry to measure the [water] absorption rate to determine the strength and type of cement used or to establish whether leaks are due to excessive porosity. The masonry probe is probably the most common test I know of." Non-Destructive Evaluation (NDE) tests include infrared thermal-imagery scans, "which evaluate temperature differentials within a building envelope " — the exterior walls and other spaces, including the roof, that together comprise the building perimeter — "and can be used to locate water infiltration."

Another NDE utilizes a linear polarization resistance (LPR) meter, which measures the presence and the rate of corrosion, the corresponding amount of steel loss and estimated time before the steel cracks, and whether and where there are voids present where the corrosion has eaten through. Because corrosion is dependent on temperature and humidity, calculations are more accurate if made over the course of a year.

Such advanced structural tests start at about $600 for a masonry probe plus the cost of any scaffolding that may need to be installed for non-street-level work. If the removed material needs lab analysis, add about $1,000. Infrared imaging can run between $1,000 and $3,000, with the cost depending "on the extent of the area being surveyed and the extent of the reporting level you need," says Aspegren.

Whichever advanced test you use, the ultimate goal is to help a building engineer determine if there's structural degradation, and to give him or her data about how the building was built, "which is critical," says Aspegren, "to the preparation of construction documents."

Adapted from Habitat January 2008