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Ask the Engineer

The Ongoing Battle Against Leaks

I’m on the board of a cooperative that has been plagued with recurring leaks for the past several years. During that time, the board has hired three different contractors for repairs, which have included replacing the roof, repairing defective brickwork, repointing mortar joints, and caulking windows. Yet even after all the work, water is still getting into several apartments. What’s the best way to find and fix leaks, particularly ones that persist after repair work?

Leaks are probably the most common headache suffered by building owners, managers, and residents. Despite major advances in building materials and construction methods, water remains a formidable foe. A leak can start from an opening as small as a pinhole, and left unrepaired, can develop into a significant and costly problem. Over time, water can penetrate through layers of brick, steel, concrete, wood, and insulation on even the most imposing fortress of a building. Traveling the path of least resistance, it finds the weakest links in the building’s chain of components and systems, wreaking havoc along the way. In addition to the obvious annoyance of a leak, over time water infiltration can cause serious structural damage.

Tracking the Source of the Nile
The telltale signs of leaks are usually readily apparent: dripping water from ceilings or walls; moist surfaces; peeling, bubbling or cracking paint; stains or discoloration; mold or moss; efflorescence (a whitish powdery residue from leaching salt); and general deterioration or corrosion. The source of a leak, however, is not always as obvious. Because water travels so freely, the area where a leak reveals itself may be far from where it originated.

The majority of leaks start on the exterior envelope (the external surface) surrounding the building, such as roofs, walls, windows, doors, terrace, balconies, chimneys, and bulkheads. Any area that has deteriorated or been damaged is a potential weak spot for rain, snow, or ice to penetrate interior spaces. Particularly vulnerable are joints or junctures where vertical and horizontal surfaces meet, such as the roof membrane and the parapet or the window frame and windowsill. Also susceptible are areas where two different types of materials join, especially if they lack flexibility and tend to harden and crack, such as stucco and brick.

Two other major sources of water penetration are internal leakage associated with plumbing and HVAC systems, and leaks from groundwater seeping through foundation walls and basement floors.

The Usual Suspects
To determine the source of a leak, an engineer will line up the usual suspects and address the most probable causes in a process of systematic elimination. Sometimes the preliminary diagnosis is straightforward: rainy day leaks, especially those that increase with the intensity of the storm, most likely mean the building’s waterproofing has failed, while a continuous leak, even on sunny days, points to a plumbing or heating problem. An intermittent leak suggests the cause is triggered by the operation of some water-related system, such as when a bathroom ceiling fan leaks whenever the resident on the floor above takes a shower.

Some leaks require methods of detection beyond simple observation. Occasionally water needs to be directly applied to suspected problem areas to see where the leak originates. For suspected leaks behind walls, a hand-held meter is used by inserting its probes into the surface to measure the amount of moisture. Another leak-detection tool is infrared thermal photography, which reveals cooler spots on a surface, suggesting moisture behind the wall.

There are other factors to consider when determining the cause of the leak, such as: How long has the spot been leaking? Over how large an area does it leak? Has the spot been previously repaired? What materials have been used in the repairs? What is the age and overall condition of the building? How well is the building maintained? The answers to these questions provide leads for tracking down the source(s) of the problem.

Stopping the Flow
Diagnosing leaks is one thing; curing them is another. Unfortunately, there are no magic bullets, and in most cases no guarantees, for stopping water penetration. Although boards are understandably frustrated when repairs are made and the building still leaks, waterproofing fixes are not always a one-shot deal.

While the assumption may be that the leak originates from just one place, often the culprit is multiple sources. The best an engineer or contractor can promise is to approach the problem through an educated, carefully planned “trial and error” process, tackling the most obvious causes first and seeing what effect the repair has on the leakage.

For example, it may have been obvious that roof-level repairs addressing the roofing membrane, parapet, and chimney bulkheads were needed to stem leakage, yet hidden defects in counterflashing were not readily apparent. In such cases, repairing the most obvious spots will likely slow the leakage, but water penetration will persist until all the problem areas are addressed.

The board’s repair budget, the severity of the leak (drip versus a deluge), and location (basement versus a bedroom), will usually dictate the plan of action. If the board is working with limited funds and the leak can be pinpointed with relative certainty, it makes sense to go ahead and make the necessary repair(s) rather than spend tight funds on potentially redundant testing. Depending on the building’s condition, certain repair items (e.g., brickwork, pointing, caulking, flashing) may need to be addressed for general maintenance anyway, even if they turn out not to be the cause of the leaks. Such items are part of the testing equation: so long as they are left in disrepair, the engineer or contractor cannot rule them out as contributing to the water infiltration.

An Ounce of Prevention
The most basic—and in the long run, least expensive—way to prevent leaks is an ongoing program of proper building maintenance. The effects of weathering demand continual vigilance to identify developing trouble spots early on. Materials such as caulking and coatings, for example, often last an average of only five years.

The building’s maintenance staff should conduct routine periodic inspections at least two or three times a year, keeping an eye out for such warning signs as ponding on roofs, cracks in brickwork or coatings, openings in joints, staining, surface deterioration, and other signs of water infiltration. The board should also periodically survey residents about any moisture in individual apartments.

The effects of the elements aside, an all-too-frequent cause of leaks is inappropriate use of the roof. Roofs should not be used as terraces, gardens, or recreational areas unless specifically built for such purposes. Planters, jungle gyms, pools, tables, chairs and the like can compromise the structural integrity and waterproofing ability of a roof that has not been designed for such use. In addition to the safety risks, turning your building’s roof into a combination gym/playground/cabana will quickly turn top-floor apartments into catch basins.

A regular maintenance program and respect for the building’s roof will head off the need to make rash repair decisions at a bad time of the year at less-than-competitive prices. Making timely fixes to the building’s exterior will keep minor problems from becoming major ones and avert the heartache of fighting a losing battle against leaks.

This column was originally published in the March 2003 issue of Habitat Magazine.

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