Alpine Research Facility Update: Managing Snow on Synthetic Slate Shingles

Winter conditions in the eastern region of the U.S. have been relatively mild this winter. I’m a little cautious as I write this article because last year, the Midwest and eastern regions of the U.S. received a good deal of wet, heavy snowfall in March and April (snowfall that was very liquid or viscus compared to what we have experienced to date this year). While this article touches on observations made from our roof mock-up research facility in Morrisville, Vermont between the periods of mid-January to early March, we hope that there will be additional opportunities to collect data as we move further into March and April.

This information will be broken into several parts over a series of posts. First up (today), is a report on the synthetic slate shingles. We’ll follow with a report on composition shingles, corrugated metal, slate and tile, and last but not least, membrane and solar panels.

Observations on Synthetic Slate Shingles

For those of you who’ve been following this winter roof mock-up research experiment that compares snow management system performance on three different roof types (side-by-side, all on one structure), you may recall that the building is a salt box design with a 7/12 pitch on one side and a 12/12 pitch on the other. The 7/12 pitch faces Northwest, while the 12/12 pitch faces Southeast. One roof area is synthetic slate shingles, the second area is composition shingles and the third area is corrugated metal.

We chose to divide the synthetic shingle portion on the 12/12 pitch into two different installation layouts using our new Fusion-Guard system. On the left side of the synthetic shingle section, we installed Fusion-Guard “pad-style” snow guards and spaced them 24” on center. We then added our Fusion-Guard optional rod detail to create a mini pipe-style system.

On the right side, we used the European layout approach, using Fusion-Guard pads only, with a 12” spacing (see image below, dated 1/14/2020). Notice the obvious aesthetic difference. The pads on the left, spaced 24” O.C., have snow rods running between them, which are barely visible. The pads on the right do not have rails connecting them, but due to the tight 12” O.C. spacing, they seem much more obtrusive. 

The below timeline outlines our observations and the data collected over the past 6+ weeks:

JANUARY 14th

On January 14, 2020, we completed the Fusion-Guard installation on the 12/12 pitch side of the roof. The timing was great because on the night of the 16th, we received 6” of light snow. This snowfall event was accompanied by high winds out of the west, which is on the 7/12 pitch side. The wind lifted and transferred most of the snow that landed on the 7/12 pitch side right up over the peak of the building, redepositing it onto the 12/12 pitch side (see video clip below). You’ll notice in the video that the peak of the roof is visible. The drifting snow accumulated into a nearly 12” deep cornice near the peak. Below this cornice, the snow accumulation is more even in depth, but tapers slightly to less accumulation towards the eaves.

Over the next several days, temperatures were very cold, as you can see from the image above, dated 1/17/2020. Notice that the snow at the eaves is barely as deep as the height of the Fusion-Guard. This is due in part to the windy conditions, and is also a result of compaction that occurs as the snow settles. It’s difficult to see in this photo, but the cornice at the peak, although condensed to roughly 8”, is still there and is still deeper than the accumulation at the eaves.

Notice that the Fusion-Guards installed with rods on the left side of the mock-up are somewhat exposed. We have several theories about this:

  1. The guards on this side were installed on top of the first course of shingles. This is a significant departure from traditional snow guard layouts that start on top of the 3rd row of shingles. Why? …Why not? When Alpine started back in the early 90’s, we were focused on natural slate (see our “About Us” page). We were concerned about cantilevered loads on old slate roofs, as well as ice damming on poorly insulated and ventilated structures. Therefore, we set the industry standard of placement on the 3rd course of shingles that all snow guard manufacturers follow.However, synthetic shingles are typically being installed on buildings that are designed to meet building codes for snow loads. This means they’re designed to handle the accumulated weight at the eaves. In addition, most of these projects are properly insulated, properly ventilated and have the added protection of Ice and Water Shield installed under the shingles to protect the structure if ice damming should occur. Therefore, why not install snow guards closer to the eaves on roofing materials other that slate and tile? This would certainly be an advantage to building owners. NOTE: The Fusion-Guard pads on the right side of the mock-up were installed on top of the 2nd course of shingles, in order to test a more traditional approach. The butt of the Fusion-Guards on the left side of the mock-up (sitting essentially at the eaves) became exposed within a day, as snow fell away at the eaves. This started an interesting and unexpected melt at the eaves, as the snow guards began to absorb solar radiation.
  2. Notice the wide soffit on the mock-up. This building was constructed using trusses that were engineered to meet the local building code (70 psf ground snow load). There was no issue with cantilevered loads.
  3. We believe that the Fusion-Guard system on the left side of the mock-up (the system connected with rods) has experienced thermal transfer due to the system being exposed at the eave and interconnected by rails. You’ll notice in the timeline of photos that follow, that this becomes more evident over time.

JANUARY 24th

Melt started becoming evident on January 24th, after a few days of consecutive daytime temps in the low-to-mid 30’s. This allowed the mass to begin a slow melt. Note the difference in melt between the left side that is interconnected with rods and the right side that is not.

FEBRUARY 7th

On February 7th a subsequent snowfall event occurred, adding an additional 10” of wet, heavy snow on top of the already existing mass. This second snowfall event stayed in place similarly to the first 6” we received.

During the last week of February and into the first week of March, temperatures rose in our area, with a high reaching 51° Fahrenheit. In addition, rain fell on top of the existing snow mass, transforming it into an even wetter, heavier, concentrated accumulation of snow and ice. At no point did we witness a sudden release of snow or ice from either of the snow guard installation layout techniques used on this synthetic slate, 12/12 pitch mock-up.

FEBRUARY 10th and FEBRUARY 23rd

We did notice some dripping at the eaves starting on February 10th, and a consistent melt up until February 23rd, when the lower half of the roof was almost completely clear of snow and ice.

FEBRUARY 28th

Then, on February 28th, we received yet another storm, resulting in 7 more inches of fresh snow.

Based on the snowfall events and temperature swings we documented during the month of February and extending into early March 2020, it’s our conclusion that both of the snow guard installation layout techniques employed on this mock-up were nearly 100% effective, given the type of snowfall and winter conditions experienced during this time period.

MARCH 5th

As of March 5th, the only snow remaining on the roof was along the top tier of snow guards, as shown in the photo below. This is where the snow depth had been the deepest due to the drifting snow that resulted in a cornice at the peak of the mock-up.

Preliminary Conclusions:

It’s important to understand that snow varies in density. It’s likely that a late winter, wet, heavy snow would have behaved differently on these two installation methods. We believe that the initial light, compacted snow formed a bridging layer of snow mass around the guards on both sides of the mock-up. It could be argued that the conditions we experienced in January and February were ideal. We have not yet experienced a wet, heavy snowfall event like the event that blanketed the central and eastern regions of the U.S. last April.

We believe that the Fusion-Guard system, with pads spaced 24” o.c., and with rods connecting the pads, will perform better in a wet, heavy snowfall event on a roof that has no accumulated mass that has bridged. We hope to have another opportunity to collect additional information in what remains of this winter of 2020.

Customer feedback suggests that the 24” pad spacing is far more attractive than the 12” pad spacing incorporated in the European approach, as shown on the right side of the roof. In addition, the 24” spacing averages 12 pads per roofing square (10’ x 10’ roof area) vs. the European approach, which averages 30 pads per roofing square on a 12/12 pitch. Obviously the 24” spacing (12 guards per square) without rods on traditional shingles like slate, tile, composition, metal, etc., is far less expensive than the European approach, at 12” O.C. (30 guards per square). Even on synthetic shingles (the ones that incorporate Polyolefin plastic), the Fusion-Guard system with rods is less expensive to purchase, faster to install and requires half as many penetrations in your otherwise “perfectly installed’ roof.

Pad? Or pipe? The choice is yours. Both seem to perform well in the conditions tested this year. However, rest easy – in either case, when the Fusion-Guard pads are used, the optional rods can be added to either layout at any time

I’m always open to reader comments and/or questions. If you have one you’d like to ask, feel free to email me directly at brian@alpinesnowguards.com. Alternatively, you can ask your question in the comments section of this post.

We look forward to sharing further results with you as they become available.

Until then….

Brian Stearns

President & Founder, Alpine SnowGuards

We keep snow in its place

www.alpinesnowguards.com

info@alpinesnowguards.com

888.766.4273

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