Technical Details: When Is it Time to Replace the Roof?
March 1, 2010
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Roofing contractors are continually asked to provide
technical decisions by building owners. The most frequently asked question -
particularly in these tough economic times - is whether the roof needs to be
replaced or if repairs can be made to extend the service life.
Roofing contractors are continually asked to provide technical decisions by building owners. The most frequently asked question - particularly in these tough economic times - is whether the roof needs to be replaced or if repairs can be made to extend the service life. To properly answer this question a roof evaluation inspection should be performed to determine the existing condition of the roof system. The inspection should be conducted by someone who is knowledgeable in material forensics and has the proper equipment to perform the inspection.
The roof replacement/roof repair decision is largely determined by the condition of the existing roof components and materials. The inspection should focus on the condition of the insulation and/or deck, the membrane and the flashings. Standard test methods for insulation moisture analysis and membrane condition should be utilized to properly assess the roof’s condition.
Insulation Tests
The inspection of the insulation requires specialized equipment and testing to determine the presence of moisture. Moisture analysis can be conducted with non-destructive testing equipment such as capacitance meters, infrared cameras or nuclear gauges. Regardless of the type of test equipment utilized, the most important part of the moisture analysis is verification and confirmation of the tests through extraction of test cores in the wet areas.
Each 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; they are 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 types of insulation 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. 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 19 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, then the gravimetric moisture content might be 190 percent. However, if the same 29 percent volume 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.
Wet insulation must be removed from the roof system. Industry standard requires total roof replacement if more than 25 percent of the roof area has wet or saturated insulation.
Membrane Tests
Typically, the condition of the membrane and flashings can be determined through an extensive walkover inspection that identifies openings, splits, deformations and material deterioration. There are instances when irreparable membrane surfaces can be identified through visual inspection. Surface defects such as extensive blistering, ridging and openings are signs of defects that are beyond economically particle repairs. There are instances where visual observation may not be enough to determine the true membrane condition. In these cases more extensive testing is required.
The service life of a roof system depends on the condition of the roof membrane. Surface defects can be identified by the visual observations conducted in the inspection phase; however, the true condition of the membrane can only be identified by physical tests conducted in a laboratory. Each type of roof membrane has its own failure modes. Therefore, the laboratory testing differs for each type of roof membrane system. Test procedures and analysis for the major roof membranes should be completed in accordance with ASTM standards.
The roof evaluation should also identify if there is improper anchorage of the roof system components to the structural deck. If this condition exists and there is no practical way to properly anchor the roof component to the deck through repair methods then replacement is required.
An interior inspection of the underside of the deck should be conducted if feasible to assess the condition of the deck. All identified deteriorated decking should be marked on the roof area and flagged off as a potential fall-through hazard.
If the inspection concludes that roof re-cover is acceptable, all wet insulation should be removed. Re-cover application should be completed in accordance with the manufacturer’s requirements using authorized materials.
Roofing contractors are continually asked to provide technical decisions by building owners. The most frequently asked question - particularly in these tough economic times - is whether the roof needs to be replaced or if repairs can be made to extend the service life. To properly answer this question a roof evaluation inspection should be performed to determine the existing condition of the roof system. The inspection should be conducted by someone who is knowledgeable in material forensics and has the proper equipment to perform the inspection.
The roof replacement/roof repair decision is largely determined by the condition of the existing roof components and materials. The inspection should focus on the condition of the insulation and/or deck, the membrane and the flashings. Standard test methods for insulation moisture analysis and membrane condition should be utilized to properly assess the roof’s condition.
A technician weighs samples of insulation after
it has been dried to determine the gravimetric moisture content.
The inspection of the insulation requires specialized equipment and testing to determine the presence of moisture. Moisture analysis can be conducted with non-destructive testing equipment such as capacitance meters, infrared cameras or nuclear gauges. Regardless of the type of test equipment utilized, the most important part of the moisture analysis is verification and confirmation of the tests through extraction of test cores in the wet areas.
Each 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; they are 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 types of insulation 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. 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 19 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, then the gravimetric moisture content might be 190 percent. However, if the same 29 percent volume 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.
Wet insulation must be removed from the roof system. Industry standard requires total roof replacement if more than 25 percent of the roof area has wet or saturated insulation.
Membrane Tests
Typically, the condition of the membrane and flashings can be determined through an extensive walkover inspection that identifies openings, splits, deformations and material deterioration. There are instances when irreparable membrane surfaces can be identified through visual inspection. Surface defects such as extensive blistering, ridging and openings are signs of defects that are beyond economically particle repairs. There are instances where visual observation may not be enough to determine the true membrane condition. In these cases more extensive testing is required.
The service life of a roof system depends on the condition of the roof membrane. Surface defects can be identified by the visual observations conducted in the inspection phase; however, the true condition of the membrane can only be identified by physical tests conducted in a laboratory. Each type of roof membrane has its own failure modes. Therefore, the laboratory testing differs for each type of roof membrane system. Test procedures and analysis for the major roof membranes should be completed in accordance with ASTM standards.
The roof evaluation should also identify if there is improper anchorage of the roof system components to the structural deck. If this condition exists and there is no practical way to properly anchor the roof component to the deck through repair methods then replacement is required.
An interior inspection of the underside of the deck should be conducted if feasible to assess the condition of the deck. All identified deteriorated decking should be marked on the roof area and flagged off as a potential fall-through hazard.
If the inspection concludes that roof re-cover is acceptable, all wet insulation should be removed. Re-cover application should be completed in accordance with the manufacturer’s requirements using authorized materials.
