Snow Melt on New England Roofs

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Author Message John Regener, AIA, CCS, CCCA, CSI, SCIP Senior Member Username: john_regener Post Number: 581 Registered: 04-2002 Posted on Monday, October 01, 2012 - 09:10 pm:    I have much experience with snow country design in California's High Sierra Nevada mountains (remember Squaw Valley and the Olympics? It does snow heavily in some California mountain locations). However, I've learned that California snow is not the same as Alaska snow or Colorado snow or New England snow. I have a project in Massachusetts with large barrel roofs. The buildings are motion picture and television production soundstages. The design has the barrel roofs terminating 4-6 feet inside the parapets of the buildings' perimeter tilt-up concrete walls, leaving a space that will fill with falling snow and snow sliding down off the barrel vaults. PVC sheet membrane roofing will be applied on both the barrel vaults and the cricketed low-slope roof between the parapets and the bottom edge of the vaulted roofs. The architect wants me to specify a heated mesh, to be installed under the PVC membrane roofing, to melt the snow. The melt water will run across the roofing and will be directed to scuppers in through the tilt-up concrete walls, and then down large, exposed sheet metal downspouts. There are no internal roof drains here but there will be on other buildings in the complex which will alos have the PVC roofing. Recommendations for snow melt products would be very welcome. Constructive comments also would be welcome regarding snow accumulation and melting in New Englad environments. I've learned that annual snowfall is approximately 69 inches but I don't know how much to expect to be accumulated on the roofs. John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1448 Registered: 03-2002 Posted on Tuesday, October 09, 2012 - 03:47 pm:    John. Lived here for a wicked long time, so I'll give my two cents. First, you might ask the architect what their electrical engineer plans for this product. In my old office they always specified heat melt systems, though they were not usually under the roofing membrane. I'd be concerned about fastening/adhering and warranty issues from the manufacturer. (Perhaps Sarnafil since they are right here just south of Boston.) In many of my projects where snow melting systems were used, it was driven by the accumulation of snow as prescribed by the building code with concerns about exceeding the structural design loads. Sliding plus drifting behind the parapet can be quite a bit (both by code and by experience), and on the north side it could hang around a long time. If you looked at typical snow accumulations where drifting and sliding aren't a concern, I'd say that having 12 to 20 inches or so on the ground at once happens maybe every other year. But then there are occasional years where there are 40 or more on the ground at once. Temperatures can be hovering around freezing for weeks at a time, so melting in the shade would be slow. So, yep, there can be a lot of snow on the ground at one time. Unfortunately, I don't have a particular product to recommend. Maybe my former colleagues who occasionally come here can comment. Steven Bruneel, AIA, CSI-CDT, LEED-AP, EDAC Senior Member Username: redseca2 Post Number: 375 Registered: 12-2006 Posted on Tuesday, October 09, 2012 - 07:11 pm:    I am an ignorant long term resident of San Francisco, so please correct me. If you have warmed the snow to melting enough that it start draining through the scupper to the downspouts, don't you have to heat them too? Or something like this might happen? http://imgur.com/Jz82i John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1452 Registered: 03-2002 Posted on Wednesday, October 10, 2012 - 10:51 am:    Downspouts are not typically heated, presumably because once the melt water is moving it is less likely to freeze. However, they are vulnerable to freezing, and do. A formed-metal downspout that freezes will sometimes split open at the seam. For this reason you will sometimes see three-sided formed sheet metal downspouts (think square gutter vertical). However, this is not universal by any means. It is very difficult to predict exactly whether this will be a problem because there are so many factors: seasonal weather patterns, particular storms, exposure to sun, amount of roof surface, heat loss through building envelope (which can also serve to prevent ice buildup), colors of materials, etc. I think it is not terribly uncommon to rework, add or tweak heat trace systems after the fact. The reason for the trace is important because ice formation is common and frequent on lots of buildings. If there's no leak (due to good design of the roof edge) and no danger to structure, and limited concern about icicles falling on pedestrians, ice formation is not per se a problem. J. Peter Jordan Senior Member Username: jpjordan Post Number: 503 Registered: 05-2004 Posted on Wednesday, October 10, 2012 - 11:04 am:    Growing up in south Texas, I often wondered about living where I could enjoy a "winter wonderland." I was 9 years old before I experienced snow at my house (snow flurries actually). I missed out on building snowmen, sledding, ice skating, etc. I can honestly say that for 98 percent of the buildings on I have been involved in the design, there has never been a problem with ice formation. There are certain things that I am glad to have missed out on in my life. Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 1048 Registered: 03-2003 Posted on Wednesday, October 10, 2012 - 11:36 am:    You guys must be talking about "white hell." Its beauty is deceptive--especially when backpacking on an unmaintained trail in the Grand Canyon when the trail is covered with slippery snow at the upper levels. If it were not for my walking stick, a rock, and a bush, my trip down the Canyon wall would have been very short. Ron Geren, AIA, CSI, CCS, CCCA, SCIP www.specsandcodes.com Robert W. Johnson Senior Member Username: robert_w_johnson Post Number: 216 Registered: 03-2009 Posted on Wednesday, October 10, 2012 - 11:36 am:    You mean like missing out on hurricanes? I know people who love snow, but I have yet to meet anyone who loves hurricanes! Craig J Froeter (Unregistered Guest) Unregistered guest Posted on Tuesday, October 23, 2012 - 03:17 pm:    Having spent 25 years in the roofing business in northern Illinois and spent many winters trying to thaw out scuppers due to heat loss melting the snow and it freezing in the scuppers blocking the drainage I have some insight to offer. The problem with heat tapes and items of that nature you do not know they are not working until they are not working. Now it has been a few years and I hope those products have improved but in my day they did not last very long. An easier way to melt the valleys is to have a given area with minimal insulation to melt the snow that is if the buildings are always heated. It would not decrease the total building envelope R factor by much. If you have exterior scuppers and downspouts they will freeze if not heat taped, especially the north side of the building. They will freeze shut given the right conditions and you know what that will cause. If they are on the south side you can make them out of a dark material that will help to keep them clear on the sunny days. Also given the situation of a couple of years ago around Boston when the rains came after the heavy snow and all the buildings fell down you do not want to risk a frozen shut scupper. So there are two ways to go, hang on to all the snow until the weather melts it naturally or melt it all off all the way to the ground. So you need to keep the roof white with lots of insulation and build the valleys to hold whatever they may get or put on a roof with the highest solar gain, a warm valley and heat taped scuppers and downspouts or open faced scuppers and downspouts which don’t do much during heavy summer rains to contain the water. Once they freeze up and if it is causing a problem like leaking or too much weight on the roof, ice melt/salt is about all you can do without damaging the roof but it will damage the metal scuppers and downspouts. It makes for some very cold and wet days for whoever has to get the water running again, don’t miss those days. [added by Colin] Craig Froeter President - Froet Industries Roof Drains ken hercenberg Senior Member Username: khercenberg Post Number: 349 Registered: 12-2006 Posted on Tuesday, October 23, 2012 - 05:35 pm:    Thanks for the input Craig. I too have been under the impression that heat trace tends to fail over time and, as you noted, there's no way to know until you need it and it's not there. Coming back after the fact and repairing it is hit-or-miss and not cheap. I'm not sure, but I'm under the impression that energy codes nowadays dictate the minimum R-value allowed at roofs, not average like in years gone by. I wonder if there is any good, effective, long-term way to heat roof drain leaders from below so they actually radiate heat all the way up to roof level. Of course that will probably cause other problems in terms of condensation at metal roof decks as we create dew points under the roof. Randall A Chapple, AIA, SE, CCS, LEED AP Senior Member Username: rachapple Post Number: 67 Registered: 12-2005 Posted on Wednesday, October 24, 2012 - 12:47 pm:    We just looked at doing snow melt with a PVC roof and it was a no go. Most of the snow melt systems need to be in a heat sink (like concrete) that can be heated up and melt the snow. Linda May (Unregistered Guest) Unregistered guest Posted on Thursday, November 08, 2012 - 05:18 pm:    From a facility management perspective, regular house keeping of the roof drains and scuppers are necessary no matter how good the melt system works. We've been out on numerous job sites reporting roof leaks, and even with the melt system in place a clogged drain was to blame. Beware of the size of the heat wire in a down spout also as it can actually obstruct the drainage where small leaves and debris normally would have passed through. This is one area when human contribution can not be replaced. The drains need to be inspected to ensure they are functioning as intended. Linda May, CEM, CIC Roof Drain Marker Co.