It’s been an especially snowy winter in many Alaska communities, and that has homeowners and business owners asking the question, should I shovel my roof? And the follow-up question, how do I do that without getting injured or breaking the bank? Talk of Alaska consulted two engineers for answers. Daniel King is the plan review engineer for the City of Anchorage and Scott Hamel is a professor at the University of Alaska Anchorage Department of Civil Engineering.
Below are some excerpts from this program. You can hear even more answers by listening to the full show.
Listen:
Q: I'm going to start with a big question. Should I shovel my roof?
Scott Hamel: I think in general, the answer at the moment is no. I think that, you know, we haven't reached our design snow load yet, but we're getting close. And we know we have a couple more months of winter. We don't know how much more snow we're gonna get. But, you know, like you said, I think people should start thinking about it because we are getting kind of close. It depends a lot on your house, or if you're a commercial owner, what kind of roof you have.
Q: If we have been working with the 40 pounds per square foot standard (Anchorage's design snow load) in Anchorage for a while, and we haven't exceeded that this winter, what is causing some roofs to buckle?
Daniel King: The nine that we have responded to at the Building Department in Development Services, six of those have been parallel cord, metal plate-connected wood trusses. Two were vacant buildings, and one was already scheduled for demolition. And then the other one was actually a pre-engineered metal building from the 60s with a nine-foot canopy overhang that collapsed. It was just bolted on. That's one that we think would be an off-the shelf-condition from the 1960s where it may not have been designed for the snow load here. The six that did collapse this winter that are these parallel wood trusses, those ones should have been designed in an era that 40 pounds per square foot was the design snow load. Anything that we've been able to see as far as construction documents say that, but what we've found is the standard of care for construction, any inspections that we would now require today on this weren't conducted back then. And it was in a time when contractors and these wood truss manufacturers were trying to get things built and put out as fast as possible. So you know, they didn't necessarily pay attention to the connections as much, what we found sometimes is the plate connections are peeling off or missing completely in some locations from some of these buildings, which would indicate just a low level of care in the construction process, or in installing them in place. So while the design snow load is 40 pounds per square foot for this building, the trusses we're finding are failing well below that, because they don't have the connections that the designer originally intended for them to have.
Q: Are there any potential risks to only clearing off part of your roof?
SH: If you massively unbalance your roof that can be bad. And then the other thing I think maybe we forgot to mention is that you definitely want to clear lower roofs first. Sort of, like my house where I've only cleared the lower roof because the upper roof is going to slide. But if you're going to clear the upper roof, you should clear the lower first because otherwise, you end up with twice as much snow on the lower roof as it's designed for. But if you massively unbalance your roof that can be bad, but massively unbalanced, meaning like you completely clear one side of your house and don't touch at all the other side of your house. I think in general, residential construction is pretty resilient.
Q: What kind of inspections can I be making on my property both externally and from within an attic to determine if I might be at risk?
SH: I would say from the attic perspective, you can actually poke your head up and see inside there. A lot of a lot of residential construction will have, as Daniel mentioned, wood trusses connected with metal plates. And if you see that, if you look at the metal plates, you can actually tell, even if you're not an engineer, you can tell if your plates are starting to peel away. If they're separated from the wood, they should be flush and flat with the wood. And there shouldn't be any sort of distortion, or it shouldn't look like the wood is scraping through, or there shouldn't be a ton of teeth marks. And so if they all look nice and flat and flush, then your roof's in pretty good shape. From, you know, deformations of walls, cracking in the top in the sheetrock, and the top of walls or roofs, sagging of roofs, all these things are sort of indications that the building is is unhappy.
DK: The longer you've been in the building, the the more you'll know your building. So you know, if in previous winters, when we haven't had this snow load, you have a door that sticks, that could be some freeze-thaw that's occurring, that's going to be standard. But if you have doors that did not previously stick that are now sticking, and you can't close it, windows the same thing. If you have new cracks in your drywall, in your ceiling, or on your walls, those are good indications that your roof is loaded more now than it has been previously and should be considered for shoveling.
Q: My question really is about the effect of the slope of the roof on snow loads... I think it's crazy to build with a flat roof up here, to be honest with you. I don't see any reason not to have a slope, at least when it melts, it'll run off.
SH: What's interesting is that the slope at which a roof needs to be, for it to slide, for anything to actually slide, is quite steep. It's steeper than you would imagine. More than 45 degrees... And it's a little bit, I think it's less, it's definitely less if you have a metal roof, a slippery roof. Maybe it's 45 degrees if it's a slippery roof, I think, and then it's like more like 60 degrees if you have an asphalt roof, so it's quite steep. That doesn't mean it won't slide if you had the right conditions, but in order to rely on that sliding to reduce the snow load, it has to be pretty steep. And this is the reason why, once you once you start to learn about that, you start to notice things. Things like, you know, in Norway, they have a lot of A-frame structures, because that's the steepness at which you can rely on on things to slide off. So yeah, steep roofs are good.
HOST: Madilyn Rose
GUESTS:
- Daniel King - Plan Review Engineer, Municipality of Anchorage
- Scott Hamel, PE, PhD - Professor and Chair, UAA Department of Civil Engineering
Related:
- Anchorage building officials are trying to identify roofs prone to fail under heavy snow
- Anchorage Spenard Builders Supply facility suffers major snow-related roof collapse
- 2 Anchorage commercial roof collapses reported in 2 days
- Roofs collapse, boats sink under the weight of Juneau’s heavy snow
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LIVE Broadcast: Tuesday, Feb. 13, 2024 at 10:00 a.m. on APRN stations statewide.
