Everything Leaks: Testing roofs to ensure watertightness at the outset

Infrared thermography
Infrared thermography (or infrared imaging) works by locating areas of increased roof temperatures caused by entrapped water within a roof system, typically within the above-deck insulation. As is the case with electrical capacitance/impedance testing, it may not produce significant results on new roof construction. Additionally, this test method is not effective with protected membrane systems after the insulation has been placed above the roof membrane, or with roof decks capable of retaining significant quantities of construction water. Examples of the latter condition include:

• lightweight structural concrete decks;
• lightweight insulating concrete decks;
• lightweight-cellular insulating concrete decks; and
• poured gypsum decks.

When used with roof systems incorporating insulation that does not absorb water, such as expanded polystyrene (XPS) or closed-cell sprayed polyurethane foam (SPF), infrared thermography has not produced adequate results. During cold weather, heat lost from the interior of a building is greater through areas of wet roof insulation, meaning the temperature of the roof surface is increased at those locations. In warm weather, solar heat is absorbed into areas of wet roof insulation and retained, creating an increase in the temperature of the roof surface at these locations. An infrared image identifies the areas of increased roof surface temperatures.

Increased surface temperatures may also be produced by several phenomena unrelated to moisture intrusion, such as:

• ponding water atop the roof membrane;
• points of heavy gravel or ballast applications; and
• under-deck heating and cooling vents.

Consequently, electric capacitance/impedance testing or nuclear backscatter testing (discussed later in this article) is typically used to verify the results of infrared thermography.

Clear weather conditions with light wind are required for infrared thermography testing. The optimal time of day for this testing is after sunset. ASTM C1153, Standard Practice for Location of Wet Insulation in Roofing Systems Using Infrared Imaging, establishes requirements for conducting both ‘ground-based’ and aerial infrared imaging of roofing systems.

Nuclear hydrogen detection
Also known as the ‘backscatter’ methodology, nuclear hydrogen detection employs a radioactive isotope to emit high-speed neutrons aimed at the roof. This method relies on the thermalization, or slowing, of fast neutrons by the hydrogen atom contained in water to locate entrapped water within a roof system. As such, it may not produce significant results on new roof construction, much like infrared imaging and electrical capacitance/impedance testing.

The measuring instrument incorporates a periodic counter that gauges the rate at which the neutron atoms are thermalized by the hydrogen atoms contained in any water present in the roof assembly. Since other hydrogen-bearing materials also thermalize neutrons, a relative base level must be established for each roof assembly prior to testing. While this system cannot determine the amount of moisture contained in a roof assembly, it can determine the difference between wet and dry insulation. American National Standards Institute/Single-Ply Roofing Industry/RCI International (ANSI/SPRI/RCI) NT-1, Detection and Location of Latent Moisture in Building Roofing Systems by Nuclear Radioisotopic Thermalization, establishes requirements for nuclear hydrogen detection related to roof assemblies.

Low-voltage electrical conductance
Low-voltage electrical conductance testing specifically locates areas of discontinuity of the roof membrane rather than entrapped water within a roof assembly. The most common system is Electric Field Vector Mapping (EFVM)—a proprietary system developed by International Leak Detection in the 1990s in Germany and introduced to North America in 2001. Worldwide, this system has tested more than 18.5 million m² (200 million sf) of membranes.

The process works by grounding a conductive roof deck, such as steel, beneath a nonconductive roof membrane, and locating places where a low-voltage electrical field goes through the roof. This is accomplished by dampening, but not flooding, the roof, and placing an uninsulated wire loop around the perimeter of the area to be tested. The wire loop is connected to a low-voltage pulsating generator that emits a one-second 40-volt charge every three seconds, creating a momentary electrical field between the wire loop and the grounded roof deck. The roof membrane acts as an insulator between the electrified wire loop
and the roof deck. Electrical charges over the moist membrane surface will be random unless there is a discontinuity or ‘leak’ in the membrane. If there is a leak, a directional current is created, which can be followed to the leak using a potentiometer connected to two probes making contact with the roof surface.

Test reports include specific numbered locations of any breach of the membrane. For nonconductive roof decks, such as wood, a conductive medium is built into the roof assembly. Common media include:

• welded stainless-steel mesh for adhered roof
  systems; and
• welded wire mesh for non-conductive substrates.

For ballasted and vegetated roof assemblies, testing can be performed with the overburden in place. For vegetated roof assemblies, the roofing manufacturer may require installation of a low-voltage electrical conductance testing system in order to issue a special warranty.