– By Jim Austin –
Manufacturers place a heavy emphasis on proper installation to prevent water infiltration even during the worst storms
Metal roofing stands up to the forces of nature as well as or better than any type of roofing material and you should know how to sell that benefit to your customers. This is the fifth in a six-part series on how metal roofing holds up against Mother Nature. Each part will focus on a different phenomenon. For this issue it’s metal vs. wind-driven rain.
Leak is the original four-letter word in the roofing industry. You never want to hear the word leak in the same sentence with a roof you installed.
Odds are, the metal roofing systems you sell and install has endured testing, including how it stands up against wind-driven rain. As you know, the toughest tests are to meet Miami-Dade standards. The test for wind-driven rain is TAS-100.
“Meeting the specs of TAS-100 gets you approval to install the tested product into the high velocity hurricane zone (HVHZ) in south Florida,” says Chad Buhrman, Industry Manager — Roof Services at Architectural Testing Inc. “Being the most stringent dynamic water infiltration test for roof coverings, TAS-100 test results have been used outside of the HVHZ for marketing purposes by manufacturers.”
Buhrman says the test consists of water being directed at the roofing covering by a wind generator (right). Water is distributed over the roof covering at a rate of 8.8 inches of rain per hour. The test, which last 90 minutes, starts with equivalent winds of 35 mph, increasing to a top wind speed of 110 mph. The test is conducted at eight intervals with “rest stops” between each wind speed increase.
The test report includes a detailed description of the roofing system, including the underlayment, with failure characterized in two ways:
1. Any test specimen which exhibits water infiltration through the sheathing shall be considered as failing the wind driven rain test.
2. Any test specimen which has the prepared roof covering or any portion thereof blow off, tear or blow upward without reseating during the test shall be considered as failing the wind driven rain test.
Make sense?
“A properly installed metal roof should not be affected by wind-driven rain,” says Jim Bush of ATAS International. “We’re installing a roof that we’re expecting to last 50 to 100 years so with our flashing details, we recommend a redundancy in waterproofing. Overkill is good. Anything can go wrong during an installation, so we recommend secondary waterproofing methods to account for any potential sins committed during installation. It’s a minimal expense when you’re talking about a $20,000 metal roof to spend another $200.”
So ATAS details include provisions for the harshest conditions, including wind-driven rain even in areas where hard winds and rain are not common. For instance, ridge assemblies (bottom photo) are installed to keep out wind-driven rain, but also include a back-up secondary closure. “We don’t differentiate methodology for different regions,” Bush says. “We design our details for those 100-year storms. Other products, like asphalt shingles, are installed with details for 20-year storms.”
ATAS — like many metal roofing manufacturers — invests a lot of money in the testing of its products. There are tests for everything Mother Nature can throw at a roofing system, including wind-driven rain as well as air and water infiltration. Mock-ups, 10×10, are built and subjected to various forces at testing facilities.
Metal roofing panels can be comprised of mechanically seamed designs, snap together seams or metal shingles. Waterproofing techniques can vary depending upon the metal panel type. Yet over the span of its lifetime, certain natural and man-made phenomena may compromise parts of that system. Every component is important, from the metal down to the underlayment. It all must be installed correctly — which means, to manufacturer specifications.
Bush says those specifications are for the installer as well as the end-user. “We know they work,” he says. “Some installers find shortcuts, but eventually they’ll run into problems. I’ve had guys tell me they’ve been installing a particular detail 40 years and they’ve never had a problem. I tell them they’ve been lucky. If they follow the manufacturer’s specifications, they have backup support if something goes wrong.”
It’s safe to say all manufacturers want you to install their products correctly. The testing they pay for helps establish the specifications. Take advantage of what your manufacturers have invested in. MR
Earlier articles in this series can be viewed online.
Read the first article: Metal vs. Hurricanes and High Winds
Read the second article: Metal vs. Hail
Read the third article: Metal vs. Fire
Read the fourth article: Metal vs. Thermal Movement