Roof and waterproofing membranes and linings have long been used to protect buildings, to contain water in ponds and decorative water features, to prevent leaching of contaminants from landfills, and for other purposes. While these membranes have utility, leakage through the membranes is an ongoing problem. The efforts to contain and locate leakage have resulted in the rise of specialized consultants, air and vacuum testable membranes, and, in recent history, electrical testing methods that not only determine if a leak is present in a membrane system, but where the leak is located.
Some systems, such as that sold under the trademark SMARTEX, owned by Progeo Monitoring Corporation of the Federal Republic of Germany, detect leaks by detecting moisture in the roofing envelope. Sensors measure the combination of water vapor and temperature inside and outside of the roofing envelope and automatically transmit these data to the system computer for analysis. If the roofing envelope experiences any water intrusion, the system detects the increase in relative vapor pressure and will immediately trigger an alarm when unacceptable levels of water vapor are reached. This system has the advantage that is it able to be retrofitted to almost any existing roofing, and can also be placed in new and reroofing work.
Several other testing methods currently used in the industry test by means of electricity. One such system for leak detection is described in U.S. Pat. No. 6,225,909 to Nill. This system discloses roof vents including at least one moisture sensing element which is electrically coupled to an electrical connector in the roof vent. A portable moisture sensing circuit or device with a moisture display for indicating a degree of moisture is provided with an electrical connector which mate with the electrical connector in the roof vent. When it is time to inspect the roof, a worker carries the portable device from one roof vent to another and plugs the device connector into the vent connector to take a moisture reading from the sensing element(s) associated with each vent. Although functional, this system is disadvantaged in that it is not automated and thus depends on the skill and accuracy of a human. Moreover, with the repeated plugging and unplugging of the device connector, the elements of the system are more susceptible to wear and tear than a system that is fully automated and whose components are not regularly handled.
Many other systems and methods using electrical leak detection include an array of sensors and use telemetry, triangulation, or tomography to determine the location of the leakage. The data generation for these methods of leak location is achieved by attenuation of voltage as it travels from a hole in the membrane, which is the entry point of the current or signal, to individual sensors in the sensor array. Sensors that are further removed from the leakage point will sense less current or signal amplitude than those nearer the leakage point, which permits a triangulation to and, thus, location of the leak.
Electrically testable systems require one surface of the membrane to be charged with an electrical current or signal while the other side of the membrane is in contact with an electrical ground. The membrane itself must be electrically insulating, i.e. non-conductive. Then, if there is a breach in the membrane, the electricity flows through the breach to the other, grounded, side of the membrane. The electrical tension, i.e. the amount of current present, is measured either from the top side or bottom side of the membrane, depending upon which system is utilized, to determine where the breach in the membrane is located.
In one example of electrically testable systems, permanent sensors which measure the current are installed on the grounded side of the membrane, which is the dry underside, or bottom of the membrane. The top, or ungrounded side, is wet and subject to weather. In this embodiment, the top of the membrane is generally charged and any leakage is detected by the current flowing through the breach and being detected by the sensors underneath. This system works with any type or configuration of overburden, and at any depth of overburden. This system is limited to certain membrane systems which do not require absolute adhesion to the roof deck or substrate to be effective waterproofing elements. The types of roofing or waterproofing systems compatible with this embodiment can be either loose-laid over the deck, or applied like a built-up roof, in plies. These can also be applied directly over insulation or substrate board. In these systems, it does not matter that the sensor grid assembly interferes with the adhesion of the roofing or waterproofing. Although effective in certain circumstances, this system is disadvantaged in that it must be installed when the roof is constructed and cannot be retrofitted into an existing roofing assembly.
Another example of electrically testable systems, known as vector mapping, presents a process by which the differences in electrical tension created by a negatively charged wire loop on the membrane are measured, and the decline in electrical tension is followed to a breach in the membrane. This requires two poles, one held in each hand, and the distance between the poles allows the difference in electrical tension to be measured. This embodiment is a standard procedure for detecting leaks in roofing and waterproofing membranes. FIG. 1 schematically demonstrates how electrical tension on a membrane 11 is created. The negatively charged boundary wire 4 is activated by a computer 10, which pulses a current, which is usually at approximately thirty eight volts. The tension is indicated by the arrows, with the current field filling the wet surface of the membrane 11. Because there is no way to ground, the tension resembles the water in a bathtub, remaining relative calm and level.
FIG. 2 demonstrates what happens when a breach occurs in a membrane 11, which allows the electrical field to flow to ground. The same tension is created by the computer 22, but the flow of the current is directed to the grounding point, or hole 1, in the membrane 11. The voltage drops exponentially nearer to the hole 1 and this voltage difference is measured by the hand-held poles mentioned above. In practice, the tester will traverse the membrane 11 taking measurements until the voltage drop is found.
This system is useful with most types of bare or exposed membranes which are in contact with a grounded substrate, and can be used to detect and locate leakage under certain types of clean, conductive overburden, such as soil, ballasted inverted roofs, and certain planted green roofs. This method is particularly useful when the roofing or waterproofing system depends upon an intimate bond with the substrate—usually concrete—to provide reinforcement for its proper functioning. Unlike the first example, discussed above, which would interfere with this bond, this embodiment is done entirely from the upper surface of the roof membrane and is very effective in locating leakage. Finally, this system has, heretofore, been the only type of system that does not need to be installed at the same time that the roofing membranes are installed.
Unfortunately, the system described in FIGS. 1 and 2 has its disadvantages. Specifically, if there is anything overlaying the roofing membrane that is inherently non-conductive, such as a plastic root barrier for green roofs, or wide plastic drainage mats applied to the roof surface prior to the application of ballast, the current can no longer flow directly to the breach in the membrane and, instead, must flow along the surface and edges of the non-conductive overlayment.
FIG. 3 shows the condition in which a non-conductive sheet 13 of plastic is placed on the roofing membrane 11. The vector is now only detectable at the edges of the sheet 13, and the location of the hole 1, still in the same spot as before, is hidden by the sheet 13.
FIG. 4 shows what happens when multiple sheets 13 of non-conductive material are placed on a membrane with a leak. The current can only flow between the sheets 13, so one might know that a leak is present, but the rough location of the leak would be “somewhere under the non-conductive sheet”. This seriously impedes or negates the ability of the manual mapping procedure to accurately locate leakage. Also, the deeper and more complicated the overburden is in terms of number of overlayments, depth of soils, types of plantings, electrical conduits and other grounded elements, and topside finishes, such as walkways, fountains, and planters, the less effective the manual mapping procedure becomes. In many of these situations, manual mapping cannot be utilized at all. Moreover, this system is a manual process, thus requiring skilled manpower. Consequently, and moreover, leaks may only be detected and located when a skilled technician is present and testing.
Other similar methods include those taught in U.S. Pat. No. 7,652,481 to Vokey. In these methods, a leak in a membrane on top of a horizontal roof deck is located by applying conductive wires on the membrane underneath the aggregate in a grid pattern. A measuring and switching circuit generates voltage having a positive attached to the roof deck and a negative attached to the wires. The circuit has a relay for each wire which can be switched between a current sensor system and the negative potential. The sensor system is arranged to sense at each of the wires in turn the current flowing from the roof deck through any leak in the membrane to the wire. A microprocessor operates the relays in turn to connect all the other wires to the negative as a shield while each wire is sensed. From the output of the grid, the changes in current in the x and y directions are analyzed to locate the leak in the membrane.
Although capable of detecting leaks, these methods also have their disadvantages. Specifically, they must be implemented during construction as the positive component is attached to the roof deck beneath the membrane. Moreover, the measuring and switching circuit is complicated, and only measures the current at one wire at a time, rather than sensing the current over the entire area being tested at all times.
Therefore there is a need for a system for detecting and locating leakage in roofing and waterproofing membranes that may be installed over existing waterproofing membranes, that utilizes the principles of electrical field vector mapping but applies the principle to a permanently installed, computer controlled, always-on system, that provides a system wherein the sensor array is placed directly on top of the roofing membrane and within the electrical field created by the negatively charged boundary wire loop, that allows the sensor array to be wet and withstand environmental stress, that allows the sensor array to be located directly under conductive and non-conductive elements which would impede or negate other types of manual vector mapping, and that allows the sensor array to be positioned below any grounded or non-conductive elements.