Double-lock and batten-seam roofs put to the test
The time-tested performance of double-lock standing-seam and batten-seam metal roofs is demonstrated by the thousands of squares successfully installed by SMACNA contractors over the last century. With the proliferation of premanufactured roofing systems and the specification requirements of Underwriters Laboratories Standard 580 and factory mutual performance criteria, the SMACNA Architectural Sheet Metal Committee determined it was necessary to test the performance of geometries in the Architectural Sheet Metal Manual.
The roof specimens were assembled in accordance with the SMACNA Architectural Sheet Metal Manual. Testing was performed at the Construction Consulting Laboratories in Carrollton, Texas. All tests were witnessed by members of SMACNA's Architectural Sheet Metal Committee.
It was the intent of the committee to subject the metal roofing materials to performance tests as severe or more severe than those required by the industry. The test specimen evaluated 1-in.-high double-lock standing seams and 1.5-in. batten seams. Transverse seams were used in unsealed flat lock form and in soldered form.
Although the SMACNA manual does not have criteria for air leakage control, at the onset, air filtration and ex-filtration measurements were attempted but difficulties with the technique and chamber calibration made the results unsatisfactory. It was apparent, however, that fascia edge conditions contribute more air leakage than roof surface seams.
Each metal roofing system was subjected to a static pressure/water penetration test. This test is similar to tests performed on curtain walls and is a severe test of metal roof seam performance. In another test, the effects of dynamic wind loads induced by slipstream of air generated by a turboprop engine were evaluated while a constant spray of water was introduced over the surface of each metal roof specimen. The metal roof specimens were also subjected to structural load tests. Severe incremental positive and negative (uplift) loads were induced onto the outer surface of the metal roofing in an attempt to demonstrate the ability of SMACNA metal roof configurations to resist (static pressure) uplift loads exceeding those imposed by the UL 90 classification requirements.
Metal roof descriptionTest specimen: 6 ft. by 19 ft., 5 in.
Roof pitch: 4/12
Seam height: 1 in. standing; 1.5 in. batten
Pan width: 20.75 in. at center, 15.25 in. at rakes
Seaming: Double-lock standing-seam or batten-seam, conforming to SMACNA's Architectural Sheet Metal Manual
Fasteners: 2-in.-wide cleats at 12 in. centers, nailed with two ring shank nails per clip
Underlayment: Rosin-saturated building paper, 5 lbs. per 100 sq. ft., lapped 2 in. and nailed approximately 36 in. o.c.
Maximum sheet length used was 120 in. Transverse seams were used to provide pan-lengths as indicated on diagrams. Edge conditions were flashed with cleated 5-in. fascia, lapped 4-in. at the rake and continuous at the eave and ridge. The panels and associated flashings were fabricated and tested in each of the following materials:
16-oz. copper (standing and batten seam)
24-ga. galvanized steel (standing seam)
.032-in. aluminum (standing seam)
.015-in. Terne-coated stainless steel (standing seam)
Static water penetration testThe static water penetration test was similar to the American Society for Testing and Materials E331-86, which is used for curtain walls. This test subjected the specimen and chamber to a constant vacuum pressure equivalent to a 2-in. water head pressure. Water was uniformly sprayed on the roof at a rate of 5 gallons per hour, per square foot of surface. This test simulated what could be expected in a severe storm condition with high winds and rapidly changing exterior pressures.
An observer remained inside the test chamber for the 15-minute duration of the test to record any water leakage through the system.
All systems passed. No uncontrolled water infiltration was observed for any of the metal types or systems with the exception of the eave and rake junction with the chamber on the Terne-coated stainless steel (TCS) roof system. This was attributed to imperfect connections of the fascia junction.
Dynamic water penetration testFor this test, the roof system was subjected to dynamic loading and water exposure similar to what it would go through in a rainstorm. The test was similar to the Architectural Aluminum Manufacturers Association Standard 501.1-83 for metal curtain walls.
In this test, water was applied to the exterior of the test specimen at a minimum rate of 5 gallons per hour, per square foot of roof surface while an 80- to 85-mph slipstream of air was applied. The slipstream of airflow was produced by a turboprop engine positioned approximately 20 ft. from the eave of the specimen.
An observer inside the chamber inspected the specimen's interior during the test and the exterior of the system after the test.
All roof systems passed. No uncontrolled water infiltration was observed for any of the metal types or systems with the exception of the eave and rake junction with the chamber on the TCS roof system. This was attributed to imperfect connections of the fascia junction. No system damage of deformation occurred.
Uniform structural load and deflection testsFor this test series, a second pressure chamber was applied over the metal roof specimen but was not in contact with it. Vacuum and blower pumps were connected to the chambers to create negative pressures (uplift pressures) on the top of the roof and positive pressures (downward loads) on demand.
All systems were tested in load intervals, both positive and negative, of 20 lbs. per sq. ft. (psf), 40 psf, 60 psf and 90 psf. Each load level was applied, held for 10 seconds then released to atmospheric level. All systems were subjected to negative loads of 125 psf. The galvanized steel, aluminum, TCS and copper batten-seam systems were subjected to a 150 psf uplift load. The TCS and copper batten-seam systems were taken as high as 190 psf uplift load in an attempt to take the systems to structural failure. Deflection recordings were taken at the standing seam and at the midpoint of the panels.
From these tests, one can conclude that the correct installation of the SMACNA details on custom-fabricated metal roofing materials will perform adequately when subjected to simulated storm conditions.
We also learned that roofing felts are necessary as a second barrier for the metal roofing system and should not be eliminated. The transverse seams should be as detailed on the SMACNA Architectural Sheet Metal Manual with full closure and continuous cleating from standing seam to standing seam.
(SMACNA offers technical information on many subjects of interest to sheet metal and roofing contractors. For more information, contact SMACNA at 4201 Lafayette Center Drive, Chantilly, VA 20151-1209; call (703) 803-2980; fax (703) 803-3732; e-mail: email@example.com.)