Best Practices: Service Life Predictability of Roof Systems
September 8, 2006
The most heated debate in the roofing industry centers on the issue of roof removal versus roof repair. It is not uncommon that, on a given roof installation, three or four roof evaluators might reach three or four different conclusions relative to the roof's condition, maintenance requirements and service potential. The evaluation of the sources of available maintenance options and their economic benefits to the building owner would likely yield additional varying conclusions.
These conditions exist because roof maintenance is often conducted in the absence of a standard set of measurements, values or decision-making guidelines. For example, a 2-inch high “ridge” in the roofing membrane is an entirely different problem on a six-year-old roof than it is on a 21-year old roof. It is also different when it occurs within an organic felt system rather than a fiberglass felt system, and so on. Experts might disagree on its ultimate impact on the serviceability of a roof.
The standard of measurements and values referred to would establish the specific problems or potential problems existing within the roofs, their severity, their density and their impact on the remaining serviceability of the system. Depending on the defect type and membrane type, the roof's age, and other considerations such as climate and building occupancy, a “decision tree” process could guide the user to the most technically and economically sound course of action.
The intent of a program developed in this manner is to reduce costs, minimize maintenance requirements, and establish a level of quality assurance that would result in predictable and controllable roof service.
The program should be dynamic so that it can be upgraded and revised to reflect changing roof technology, in-house experience levels or specific user requirements.
Developing a system to rate a roof's condition, estimate its service life, and to provide a basis to make decisions or select repair alternatives is a difficult task. Ideally, the system would be based on the instrument- measured impact that each situation (such as a defect) has on the roof's integrity and condition. Each measurement would include combinations of problem type, severity level, and identify the membrane type, test sample analysis and thermal performance of the insulation component.
Such an approach would require both roof investigation and material forensic analysis in a laboratory.
Considering the complexity of roof systems and state-of-the-art roofing technology, an empirical approach is necessary to establish a procedure that will provide a disciplined and effective management tool for optimizing the service life of a roof system. Following are suggested procedures for instituting the rating and decision process. This process eliminates the subjectivity of the evaluator and is based solely on objective analysis and evidence.
The FAST Program
The goal of the Forensic Analytical Serviceability Tracker (FAST) program is to remove all subjectivity from the formulation. The service life prediction is based solely on objective evidence. All roof system components should be analyzed, inspected, and tested.
In the Forensic Analytical Serviceability Tracker (FAST) procedure a service life prediction is established within the following parameters:
1. The age of the existing roof system.
2. The industry average service life of the roof system.
3. The forensic analysis of the existing roof system, based on the roof investigation and the material analysis.
4. The identified distress factors of the existing roof system.
5. FAST rating.
The following factors are used in the FAST method of determining the existing serviceability of an existing roof system:
1. Provide the age of the existing roof system.
2. Identify the existing roof membrane system in the chart below and determine the industry average service life. (The National Roofing Contractors Association has developed an estimated service life chart for roof systems. See Figure 1.)
3. Conduct a forensic analysis of the existing system, including the insulation and the membrane. Determine the condition of the existing insulation by completing these tests: gravimetric moisture content and volumetric moisture content.
Determine the condition of the existing membrane by completing the following tests:
Built-Up Roof System
- ASTM D 2829 Standard Practice for Sampling and Analysis of Built-up Roofs.
- ASTM D 4 Standard Test for Bitumen Content.
- ASTM D 1670 Standard Test Failure End Point in Accelerated and Outdoor Weathering of Bituminous Materials.
- ASTM D 2523 Standard Practice for Testing Load Strain Properties of Roofing Membranes.
- Microscopic examination.
All roof membrane systems have defects that decrease the service life of the roof system. The major defects that have a direct influence on the service life of the roof system should be identified. Points are deducted from the FAST rating based on types of system deficiencies and frequency of occurrence. Rates are based on the deductions contained in the chart in Figure 2.
5. The FAST rating is based on a 20- point scale, with zero points being the optimal score. The deficiency deductions are tabulated by component to determine the overall roof condition. The roof condition rating scale is as follows:
5 = Good
10 = Fair
15 = Poor
20 = Bad
Roof systems that fall within the “Good,” and “Poor” categories will require the proper level of maintenance and repair. Roofs that score higher than 15 points require removal.