A fastener pull-out test is a field test used to determine how much tensile force a roofing fastener can withstand before it pulls out of the roof deck. It is especially important for commercial roofing systems that rely on mechanical fasteners to secure insulation, cover boards, base sheets, or single-ply membranes. The test helps contractors and roofing professionals determine whether the existing roof deck can provide adequate fastening strength for the proposed roofing system.
What Does a Fastener Pull-Out Test Measure?
During a pull-out test, a fastener is installed into the roof deck using the same or an approved fastener type intended for the roofing project. A calibrated pull tester, or dynamometer, is then attached to the fastener. The tester applies an upward tensile force until the fastener reaches its specified failure point. The force required to withdraw the fastener is recorded.
The resulting fastener pull-out resistance helps establish whether the fastener and deck combination can withstand the forces expected from wind uplift. According to the National Roofing Contractors Association (NRCA), pull-out resistance is an important design parameter for mechanically attached roofing systems and can also provide valuable information about existing deck conditions during reroofing projects.
Why Is Pull-Out Testing Important?
Roof decks can vary significantly in strength depending on their material, age, thickness, condition, and construction. A fastener that performs well in one substrate may produce very different results in another. NRCA research notes that fastener pull-out resistance can vary substantially between different steel deck grades and between plywood and OSB substrates.
Testing is particularly useful during commercial reroofing and roof replacement projects, where the existing deck may have deteriorated or its exact specifications may be unknown. Poor pull-out resistance can result in inadequate attachment and increase the risk of wind-related roof damage.
How Many Fastener Pull-Out Tests Are Required?
The required number of tests depends on the applicable code, project specifications, roof area, deck type, roofing system, and testing standard. For Florida projects, TAS 105 provides specific field withdrawal-resistance testing requirements for roof attachment systems.
Under TAS 105, roofs of 100 squares or less require 10 withdrawal-resistance tests. At least three tests must be performed in perimeter areas, three in corner areas, with the remaining tests conducted in field areas. For every additional 50 squares, three additional tests are required. The required number of samples is increased by 125% for gypsum, lightweight insulating concrete, and cementitious wood-fiber decks.
Other project specifications can require different testing quantities. For example, some roofing system manufacturers specify their own testing schedules based on roof area and attachment requirements. Therefore, contractors should always follow the applicable building code, approved roofing assembly, manufacturer requirements, and project specifications rather than assuming that one test quantity applies to every roof.
What Happens If Pull-Out Results Are Too Low?
If testing shows that the existing deck cannot provide the required pull-out resistance, the roofing design may need to be modified. Options can include using a different fastener, increasing fastener density, changing the attachment pattern, repairing or replacing deteriorated decking, or using an alternative roofing system.
The final test report should document the test locations, fastener information, individual results, roof and deck characteristics, and relevant statistical information. TAS 105 also requires appropriate pull-tester calibration documentation and identification of test locations on a roof plan.
Fastener Pull-Out Testing for Commercial Roofs
A fastener pull-out test is an important quality-control and design tool for mechanically attached commercial roofing systems. It verifies the actual holding capacity of the fastener-and-deck combination, rather than relying only on theoretical or manufacturer data.
For Florida commercial roofing projects, the commonly referenced TAS 105 requirements call for 10 tests on roofs up to 100 squares, plus three additional tests for every additional 50 squares, with increased sampling for certain deck types. Because requirements can vary by project, a qualified roofing professional should verify the applicable code and manufacturer specifications before testing and installation.
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Commercial Roof Coatings & Restoration
