Service Life Predictability
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. How many authorities or experts would agree 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 can 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, revised or remodeled to reflect changing roof technology, in-house experience or specific user requirements.
Developing a system to rate a roof's condition, estimate its service life, and 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 or weather) has on the roof's integrity and condition. Each measurement would include combinations of problem type and severity level. It would identify the membrane type, the climate, 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.
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 that eliminate the subjectivity of the evaluator.
Forensic Analytical Serviceability TrackerThe goal of the Forensic Analytical Serviceability Tracker 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 FAST procedure, a service life prediction is established within the following parameters:
The age of the existing roof system
The industry average service life of the roof system
The climatic conditions in the geographic area of the facility
The forensic analysis of the existing roof system, based on the roof investigation and the material analysis
The identified distress factors of the existing roof system
FAST FactorsThe following factors are used in the FAST method of determining the existing serviceability of an existing roof system:
Provide the age of the existing roof system.
Identify the existing roof membrane system in the chart below and determine the industry average service life. (The National Roofing Contractors Association developed the estimated service life chart).
Roof Membrane System Mean Life Years
Natural Slate 60.3
Clay Tile 46.7
Metal Panels 26.5
Coal-tar Organic BUR 23.0
Coal-tar Glass BUR 11.2
Asphalt Glass Shingles 17.7
Asphalt Organic Shingles 17.5
Asphalt Glass BUR 16.7
SBS Modified Asphalt 15.9
Asphalt Organic BUR 14.7
APP Modified Asphalt 13.7
Roof system membrane performance can be altered by the climatic conditions within the geographic regions of the facility. For this analysis, the climatic conditions refer not only to temperatures but also other interrelated factors such as rain, wind, radiation, topography and cloud cover.
Recent studies have indicated that the top surfacing color of the membrane affects the service life in different climatic regions.
Forensic Analysis of the Existing SystemTo determine the condition of the existing insulation, complete the gravimetric moisture content and volumetric moisture content test. For membranes, perform 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
Thermoset Membrane Systems (EPDM)
ASTM D 4637 Standard Specification of EPDM Sheet used in Single Ply Roof Membrane, to include ASTM D412 Tensile Strength, ASTM D412 Elongation and ASTM D816 Factory seam strength
Mil thickness of existing membrane
Thermoplastic Membrane Systems
ASTM D 4434 Standard Specification for Poly Vinyl Chloride (PVC) Sheet Roofing, to include: ASTM D638 Tensile Strength at Break; ASTM D638 Elongation at Break,
ASTM D638 Seam Strength and ASTM D638 Overall Thickness
The roof condition investigation should determine the existing defects of the roof system. All components of the roof system should be investigated: membrane, flashings, penetrations and metal terminations. All defects should be noted and. The major defects that have a direct influence on the service life of the roof system should be identified.