Many roof replacement projects on FM-insured buildings are required to demonstrate performance via either field uplift testing or full-time onsite visual construction observation (VCO) by a qualified professional. This post has the info you need to understand the requirements and options.
What is FM 1-52?
FM 1-52 Field Verification of Roof Wind Uplift Resistance is is a document produced by the Factory Mutual Insurance Company. It is one of several FM Property Loss Prevention Data Sheets intended to “reduce risk at…existing facilities—as well as those under construction”.
FM 1-52 provides guidance for field testing adhered roofing assemblies with the intent of determining if there is adequate wind uplift resistance. The data sheet also provides an alternative method for verifying performance called “visual construction observation” or VCO.
FM 1-52 Requirements
FM 1-52 requirements apply to adhered roofing assemblies when both of the following are true:
- location is within a “tropical cyclone-prone region” (defined in another FM Data Sheet, 1-28)
- location is in an area where the design wind speed is greater than or equal to 100 mph
In these circumstances, FM 1-52 requires one of the following:
- satisfactory uplift tests
- visual construction observation (VCO)
The data sheet provides two options for uplift testing: a negative pressure test and a bonded uplift test. The negative pressure test is more common, as the bonded uplift test is only applicable when the entire assembly is adhered (no layers mechanically fastened).
Uplift Testing Limitations
The negative pressure uplift test specified in FM 1-52 has been the subject of criticism in the industry. Anecdotal experience as well as carefully controlled laboratory study have shown the test to be unreliable.
In a recent Professional Roofing article, Mark Graham (NRCA‘s vice president of technical services) writes the following in describing the NRCA’s position:
…field-uplift testing should not be relied upon as an indicator of an adhered roof assembly’s in situ uplift resistance or as a quality-assurance measure of roof assembly installation. Continuing to use it as such is irresponsible.
A more reliable quality assurance measure is full-time observation during roofing construction, also known as visual construction observation (VCO).
VCO Quality Assurance Requirements
Observation of construction work by qualified 3rd parties as a means of quality assurance is not unique to FM 1-52. However, for the purposes of this post we’re discussing “visual construction observation” (VCO) as defined in FM 1-52.
FM 1-52 Appendix F defines VCO as “full-time onsite visual construction observation during roof system installation” by a qualified 3rd party, with reporting provided “in an accurate and objective manner”.
The data sheet lays out in detail specifically what must be observed and reported on, including substrate conditions and installation and attachment of all components.
The qualifications of the observer are also spelled out. In addition to “thorough knowledge” of the relevant systems the observer must hold a certification as either a Registered Roof Observer (RRO) or Registered Roof Consultant (RRC) by the International Institute of Building Enclosure Consultants (IIBEC) for projects in the U.S.
Benefits of VCO
Full-time visual construction observation provides realtime information and feedback about the quality of the roofing work. Any issues with the construction can be identified and addressed before the work is finished.
VCO therefore provides actual quality assurance. The VCO process improves the quality of the finished product.
In-situ uplift testing, at best, attempts to demonstrate that the finished product meets spec. Since the test is performed after the work is done, it’s not doing anything to improve the quality of the work.
In roofing (and other building envelope systems) it is actual performance that matters. A leak is a leak, regardless of how many tests the assembly may have passed or how many warranties are in effect.
We are in the business of helping our clients improve the actual performance of their buildings and VCO is a great tool toward that end.
Join our growing tribe of building nerds and sign up for the best newsletter in AEC. Back of the Envelope delivers helpful info of immediate practical importance.