In my last blog I talked about the significance and importance of layout for pad-style snow guards. In short, we’ve found through trial and error that pad-style snow guards that are evenly distributed over the entire roof surface do a better job of allowing snow and ice to melt in place than individual tiers of snow guards with open roof space between them.
Picture a composition shingle band that’s 24” wide across a roof. You have 8 feet of frictionless surface between the bottom tier and the next tier. You can imagine how a snow mass letting go on the upper tier will gain momentum and simply punch any snow on the lower tier right off the roof. See the Alpine website for details on concentration of guards at the eaves and treatment of the uppermost 10 feet of roof.
Pipe-style or fence-style snow guards are used much differently than pad-style snow guards. In general, pads simply add friction that’s used to manage the slow release of the snow mass as it melts and comes off in small chunks. Pipe-style snow guards are considered “barricades,” with the intended purpose being to keep as much of the snow mass on the roof as possible while it melts and sheds off as water.
Pipe-style snow guards are also tested for shear and pull-out values. This is where I’m really struggling with a competitor’s approach to suggestions for use. I’m confident that I can construct a metal fin that attaches to rafters using nuts, bolts and flashing to prevent water infiltration and holes to retain pipes for the fence. I can test such a bracket and probably achieve values in excess of 4,000 pounds of shear and similar values in pull-out.
But what does that tell me about the performance of the fence? Add varying roof pitches, snow loads, differing materials and fence types, and I think you’d agree that the bracket testing is just one part of the equation.
If the bracket described above utilizes 3/8” diameter rods, with brackets installed 8 feet on center, imagine what will fail first. The roofing material itself is likely to fail before this bracket example.
I can’t say it often enough or more clearly: Structural values for these systems, although important, don’t tell the designer anything about performance. The only performance testing I’m aware of to date is testing that Alpine has commissioned with Northern Microclimate Ice & Snow, who has performed mock-up testing to investigate the ice and snow formation/behavior on building facades, roofs and exterior features, providing validation and/or refinement to mitigation strategies. Tests are conducted in a temperature-controlled chamber where the mock-up is exposed to multiple test scenarios of snow, ice and rain, with calibrated temperature cycling replicating the characteristics of winter storm conditions that have been known to produce ice and snow release. You can view the complete test report here, as well as watch the condensed, time-lapsed video of the actual testing that was performed.
Additional performance testing is underway for slate, tile, metal, synthetics, composition shingles and solar panels. It will be difficult to address every scenario, and we’re excited that we’ve started the process.
Alpine SnowGuards addresses pipe-style layout in one of the 3 following ways:
1. Providing your roof plan information allows us to calculate and recommend a layout for your pipe-style system.
2. We’ve designed a Layout Request Form, which calls for project-specific information. Just fill it out and send it back to us at email@example.com – we’ll send you a recommended layout and project pricing.
3. Our Online Project Calculator is an innovative tool that we’ve engineered specifically for use by architects, engineers, roofing contractors, distributors, developers and construction companies. Sign up and start utilizing the services and conveniences our calculator provides. To name a few:
- Immediate layout & project pricing
- Any-time convenience
- Store & recall your projects anytime, anywhere
- Material and finish options
- Powder coating options
- Product/system comparisons
- Complete printable overview
Below, we’ve included actual project examples that have been run through our calculator from inception all the way to project completion.
Location: Andover Old Town House, Andover, MA.
Type: Historic Renovation
Alpine product: PP225 Three-Pipe Height Adjustable Snow Management System in Brass
Purchased by: Beacon Roofing Supply
Installed by: Capeway Roofing Systems, Westport, MA
Engineering Calculations (below is an excerpt):
**Certified, stamped layouts are available when using the Online Project Calculator.
As an interesting side note, even back in 1910 there was a recognized need for snow management on the original slate roof, as seen in the image below, from the Andover Historical Society website.
To wrap things up, I thought I would share one of the best ways I can think of to describe the use and effect of pipe-style snow guards: Picture ocean water washing into shore, first encountering a reef. The reef slows the rushing water. The greater the pressure, the higher the cresting of the waves. However, if there are several tiers of reefs to slow the incoming water, the cresting waves will be much smaller by the time they hit shore.
Knowing the details of a specific roof allows Alpine to recommend the proper number of tiers to minimize, reduce or eliminate the effects of a cresting snow mass. Demonstrating this through the collection of performance data will aid greatly in layout suggestions as well as in facilitating better solutions.
If you have any questions, you can email me directly or post your question in the comments section of this blog.
Now that we’ve covered layouts for both pad-style and pipe-style snow management systems, we can get back to the evolution of snow guards. Next time, we’ll enter the 1990’s! That’s right….the era of peace, prosperity, Princess Diana, O.J. Simpson and the internet.
President and founder, Alpine SnowGuards
We keep snow in its place
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Alpine SnowGuards designs, engineers, and manufactures snow management systems from our facilities in Morrisville, VT. We work closely with leading roofing contractors, engineering firms, developers, solar installers and roofing manufacturers to ensure we deliver quality products that do what we say they’ll do. Alpine SnowGuards can help a building qualify for LEED® credits.