The Value of Roof Moisture Surveys
Moisture surveys can also be useful to roofing contractors in determining the causes of roof problems and their solutions. The surveys are valuable tools in analyzing the condition of the roof for information to estimate the resistance to heat loss of the roof system.
Moisture, in the form of water or vapor, has a detrimental effect on each component of the roof system. At the roof deck, moisture causes deterioration of the substrate, weakens structural integrity and promotes rust on metal decks. Once insulation is wet, it loses its structural and thermal integrity. It is weaker due to loss of binders and rotting of organic fibers, and thermal resistance is dramatically reduced. Moisture also causes a dimensional change in the insulation and the securement of the insulation is reduced. Openings in the membrane allow moisture intrusion into the system.
Roof InsulationThe presence of moisture in the system can best be determined by conducting an analysis of the existing insulation. Insulation is a critical component of the roof system because it provides both the thermal value for the building and the structural substrate for the roof membrane system. Investigation of the insulation should concentrate on moisture intrusion.
All insulations, once wet, lose their structural and thermal integrity. All wet insulation should be removed from the system. During the course of the investigation, insulation should also be inspected for slope to accommodate proper drainage and structural defects. Gaps in insulation panels can contribute to membrane ridges that outline the pattern of the insulation known as "picture framing." There are three primary methods to determine the condition of the existing insulation in a roof system: non-destructive testing equipment, test cut sample and laboratory testing.
Nondestructive Testing EquipmentThe advancement in technology of nondestructive moisture detection equipment has made the use of this type of instrumentation both economical and effective. The equipment has also advanced in reliability and ease of use for the operator. Moreover, it is not as burdensome in transportation or in placement to the roof area as earlier forms of instrumentation. Further advancements in technology will increase the use and reliability of these types of instruments.
Infrared scans are completed with a thermographic camera that finds areas of wet insulation by identifying heat loss from the building. The main theory of this technology is that moisture-laden insulation contributes to thermal loss. The infrared camera has the ability to read the temperature throughout the roof area and the thermograph shows the contrasting tones of the roof area at the different temperature variations. Dark tones indicate dry areas, which have lower temperatures than the suspected wet areas, which radiate higher temperatures from interior building heat loss. This technology is in comparison to an X-ray and provides a quick assessment of possible wet areas. The best possible times for infrared inspections are in the late night hours. It is also advantageous that the preceding day was clear with minor cloud cover to receive the best imagery. However, scans can be completed at any time of the year in any geographic region as long as there is little moisture on the roof surface. Infrared cameras are compact and lightweight, and new technology includes portable hand-held cameras. The scans can be completed with the hand-held cameras while walking over the roof area or through fly-over inspections by airplane or helicopter.
Capacitance meters utilize circuits that measure the difference between dielectric constants of water and the constants of most dry roofing materials. The variations of the constants obtained from a predetermined dry area indicate areas of entrapped moisture. Capacitance meters are portable and easy to operate. They are typically wheeled across the roof area in a select pattern until wet areas are indicated. The wet areas are then illustrated on a roof plan by the investigator.
Electrical resistance moisture meters are small, hand-held and battery operated instruments that typically weigh less than 18 ounces. These types of meters identify moisture content through changes in the electrical currents that are transposed through the membrane system. There is a scale at the face of the instrument that indicates the level of possible moisture content. Readings can be generated through placement over the top membrane surface.
Nuclear moisture meters identify possible wet areas with a neutron generator that emits high energy or "fast" neutrons at a target area. Some of the emitted neutrons collide and return back to the vicinity of the generator. The number of "slow" neutrons that return to the generator are counted by the instrument and give an indication of the number of hydrogen atoms in the materials. Hydrogen atoms constitute approximately two-thirds of all atoms in water, which gives an index of the amount of water in the tested areas. The nuclear moisture meters are compact and easily portable to the roof area. Moisture surveys are conducted using a prelocated grid pattern throughout the roof area at which the device is placed and readings are recorded. The grid pattern is typically 5 to 10 feet apart. The plotting of wet areas is derived from the recorded readings and identified on a roof plan.
Test CutsAfter visually inspecting all of the roof areas, making notes of all of the conditions, defects and problems, it is important to find out the true conditions of the roof system. This is done by extracting a test sample from the roof area. Test cuts are conducted in a roof analysis because visual inspections have their limitations, and thorough diagnosis of a roof system requires roof cuts.
Test cuts are also extracted to confirm the results of the walk-over roof inspections. Test cuts are required after all non-destructive testing methods are completed to correctly assess the presence of moisture or other anomalies in the roof system. Roof cuts are also made during visual inspections where there is reason to suspect that there are problems in the roof system.
Test cuts are an integral part of the roof science. Just as scientists conduct experiments to prove their theories, test cuts are analyzed to determine the condition (and cause of failure) of the roof system. Generally, we do not believe things until we see them for ourselves. Test cuts are taken at the existing roof system for two primary reasons:
To determine the roof's construction
To determine the roof's condition
In order to effectively determine the true construction of a roof system, a test cut is required. The test cut will provide evidence of the material used and application procedures. A test cut will also reveal if the as-built roof system was constructed in accordance to the proper design and specification. The results of the test cuts should be recorded.
The extraction process of test cuts is similar if the sample is to determine construction or condition of the roof system. The differences are in the type of forensic testing that is conducted on the test samples. In a roof condition evaluation, the sample test cuts are extracted to determine both the construction and condition of the existing roof system.
Laboratory TestingEach layer of insulation is considered a separate component and is tested on its own. Insulation testing concentrates on the moisture content of the applied insulation. Wet insulation is a deterrent to all roof types, because it decreases the insulation's structural and thermal capacities. Insulation is utilized as a substrate for some systems and for its thermal heating capacity. When these attributes are diminished, the roof system is compromised. There are two tests that are performed to identify moisture in insulation: gravimetric moisture content and volumetric moisture content.
Gravimetric moisture content of insulation is the percentage of its dry weight, which is the water that it contains when it is received as a sample. Gravimetric content is measured by weighing the sample as it is received and then after it has been dried. Insulation drying is completed in a convection oven in accordance with ASTM C-90. If a sample weighed 90 grams when received, and 50 grams when dry, it would have contained 40 grams of water for 80 percent gravimetric moisture content. Some insulations can absorb several hundred percent of their own weight of water.
Volumetric moisture content of insulation is the percentage of its physical volume, which is the water that it contains when it is received as a sample. Volumetric Moisture Content, which can be more useful in considering effects on insulating value, is found by dividing the volume of the sample, in cubic centimeters, by the weight in grams of the water it loses in drying. This is because one gram of water is one cubic centimeter of volume at room temperature. Therefore, a sample that is 2 inches by 2 inches by 1 inch has a volume of 65 cubic centimeters.
If a sample lost 19 grams (or cubic centimeters) of water when it is dried, its volume percentage of water was 19/65 or 29 percent. If volumetric content of fiberboard insulation is 29 percent than the gravimetric moisture content might be 190 percent. However, if the same 29 percent volume percent occurred in a light foam insulation, its gravimetric moisture content might be 950 percent, five times as much. It is important when weighing samples for moisture content to make sure to weigh any moisture that may have condensed out inside the plastic bag that contains the sample.
When properly executed, moisture surveys can be valuable tools for roofing contractors to use with building owners. The affordability and reliability of the current moisture testing instrumentation has made it possible to complete these surveys in a cost efficient and effective manner. In addition to providing time-consuming savings on identification and repair of leaks, they can also prove to be a valuable resource in securing work with a building owner. By accurately assessing whether repair or replacement of the roof system is required the contractor can earn the trust of the building owner by extending the service life of the existing system, while creating substantial cost savings, and adding to the bottom line.