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Part 1: How Wind Damages Roofs
Part 2: Hail, Ice, Snow Can Damage Roofs
By Naomi Millán, Associate Editor
October 2010 -
Roofing Article Use Policy
A weather event with damage that is tricky to diagnose on the roof is hail. The damage can be hard to see and may take a while to manifest itself, says Hoff. It may seem that the only possible damage from hail is puncture, and that it should be pretty evident. But an actual breach is an extreme event. What is more likely is the integrity of the system will be compromised, in tiny, barely perceptible ways that can have very bad consequences.
With an asphalt shingle, a modified-bitumen roof, or a built-up roof, a large enough piece of hail can lead to long-term problems, even though you can see very little damage on the top, says Kirby. "Depending on how soft the substrate is, you can get the shingle to bend enough so the bottom side can break or you may break the reinforcement but not break the top surface. That becomes a weak point." And if you get enough weak spots, you're going to end up with a shorter service life of your roof system, he says.
"The hail can create hairline cracks and punctures in the asphalt that are hard to see and won't show up for a while, but when they do show up it's a complete disaster," Hoff says. The cracks can allow just a tiny bit of water in, but not enough to get into the building. In the sun, this bit of water steams back out and can pop the granules off of shingles, for example.
For single-ply membranes, which tend to be much more flexible, lots of little dents will appear after a hail storm. The membrane itself is likely to be intact, and insurance companies are likely to say the damage is purely cosmetic. The reality is that it has the potential for a crack to develop, and also the bond in the membrane and the insulation and the substrate has been destroyed, says Hoff. Five years later there could be an extreme wind event where the roof could blow off, but the cause of that roof blowing off could have been the hail damage five years earlier, he says.
"I think this is one area where maintenance managers could be leaving a lot of money on the table, that insurance companies are not going to volunteer to give to them," says Hoff.
To avoid damage from hail, roofs have to be tough. "One of the things we know is that the tougher the substrate, the less damage that occurs from hail," says Kirby.
The less flexible the top layer, the less the bottom layer can shatter. For this reason, NRCA recommends using a cover board over the thermal insulation. "The tougher the product used, the less able to bend or depress, then the tougher the layer above it, the membrane, is going to end up being. It becomes a system effect," Kirby says.
But for systems already in place, the best thing to do after hail is find a trained inspector who can really inspect for the real effects of hail damage after a storm, says Hoff. In addition to knowing what to look for, the expert will add a layer of credibility to any insurance claims made. And even if the insurance company refuses the claim, at least a baseline has been established.
"You're able to put an insurance company on notice that perhaps in the future there could be a claim and it could be related," he says. "You can say, ok but you're on notice about that. It's been recorded and we'll keep checking."
Water in general is a trouble-maker for roofs, especially when the temperatures dip below freezing. Significant ice build up in one area of the roof could cause load issues or could damage or stress local components, like roof flashings and tie-ins to roof accessories, says Laux.
Due to a roof's configuration, there could be places where snow could accumulate in abnormal levels. If a foot of snow falls, there easily could be places on the roof where there are five feet of snow, just because of the way snow tends to blow and accumulate, says Hoff. Areas where the roof adjoins a solid wall, or where there is a lower roof such as awnings or canopies, are especially susceptible to accumulation. Hoff says canopies over truck docks tend to be especially vulnerable to loads from snow.
Liquid water present when the mercury is hovering around freezing can be the worst offender. "Some of the worse stuff can happen when you get a rain or sleety snow when it's 35 degrees at 6 p.m. and then by 9 p.m. it's 28," says Kirby. Water can get into the tiniest spaces, expanding as it freezes. "If you get water in a crack, it will freeze and expand. Then it warms up and you get more water. And then the cracks get bigger." The more freeze/thaw cycles, the worse it can be for built materials outside, he says.
There's not much to be done about freeze/thaw, except keep up on proper maintenance. Kirby gives this analogy: "Get that scratch on your car before it becomes a rusty spot and now you have to do body work."
Because a lot of the damage a roof undergoes as part of habitual exposure to the elements is cumulative, incremental or takes a while to reveal itself, it's important to create a system to track what is happening on the roof. This includes maintaining records of visual assessments with accompanying notes, says Laux, which creates a baseline against which to evaluate changes. Observations made by in-house staff could provide the baseline and segue to third-party review to evaluate potential damage from severe weather.
Hoff agrees. "Unless you have developed some way to benchmark conditions, it's very difficult to see the change that's happening," says Hoff. But likewise, it can be hard to know what to look for. "Unless you have an idea of potential cause and effect, it's always very difficult to inspect something like a roof. It's easy to get lost. It's easy to overlook things, unless you have a specific plan about what you're looking at."