Hail Resistant Roofing: 7 Minutes of BS (#BuildingScience)

Today's guest expert is Tanya Brown-Giammanco, formerly the Managing Director of Research at the Institute for Business and Home Safety and currently the Director of Disaster and Failure Studies at the National Institute of Standards and Technology (NIST). Tanya explains how hail damage works, why hail damage matters, and how to minimize damage from hailstones by selecting the right roofing shingles.

"We’re talking about hail-resistant roofing"

What hail-resistant roofing is:

hail re·sist·ant | hāl rəˈzistənt (adjective)

"A roof covering that offers significant protection from the damage caused by most hail."

—Dan Morrison, editor, ProTradeCraft

Hail, of course, is frozen precipitation that falls primarily from big thunderstorms, and we’re talking about hail-resistant roofing. Specifically, roofing systems and products that can hit back against hail damage.

That could be small-sized hail or very large-sized hail.

Either way, we want the roof to do its job.

How hail-resistant roofing works

When hail falls from a thunderstorm, it’ll fall at a specific speed based on the size of the hailstone and its aerodynamics, so when it hits a roof, its hitting with a specific impact energy.

As an editor, I love hearing people use the word IMPACT correctly. So the impact from a bowling ball is greater than the impact from a marble, partly because of the size of the ball but also because of how fast it was dropping on your roof.

When that occurs, that impact energy will be focused and spread on the material that it hits.

If it hits a wine glass, the glass will shatter. If it hits a trampoline, we have a whole new set of problems.

Because most roofs aren’t made from trampolines or wine glasses, IBHS tests a lot of asphalt shingles within different roof assemblies.

The higher the impact energy at the time of impact, the more likely you are to sustain damage. But that’s not all there is to it. The hardness or strength of the hailstone matters as well.

Hailstones that are very hard that hit a shingle surface are more likely to cause dents or tears, and hailstones that are softer are more likely to cause granule damage on an asphalt shingle. So the hailstone characteristic themselves matter, and the roofing material matters as well.

A roofing material that is very rigid, like tile or metal, is going to respond differently than a material that is more pliable, like a shingle. So both the hail physics and the material characteristics of the thing that’s being hit, both dictate the kind of damage that’ll be produced.

So part of the problem is the hail: is it a bowling ball or a marble? And how dense is it?

You can get any kind of hail anywhere, but you can also hedge your bets based on past hail storms as to what kind of hail you’re likely to face.

Aside from moving your house to somewhere with statistically less hail, the main solution is the roof cladding and the roof assembly.

Is it a wineglass or a trampoline?

Why hail-resistant roofing matters

And that kind of sets up the why-it-matters discussion.

Hail storms cause, on average, about 10 billion dollars of losses per year—most of that is due to damage to roofs.

Hail is generally not something that causes a life safety issue, so it doesn’t necessarily get the same amount of attention from media…

Hey, it’s getting attention from this media outlet.

But the fact is that it's very costly, and it costs the insurance industry boatloads of money

Boatloads.

…every single year. It’s one of those nuisance hazards, there are no good years and bad years with hail, it’s pretty consistently in the ten billion dollar range.

It also can be quite a nuisance for homeowners or business owners. If you live in an area, say Oklahoma City or Dallas, where you have hail storms that produce two and three-inch hailstones every two or three years, that’s a lot of money you, as the building owner, are shelling out in deductibles

Not to mention hiring contractors and living in a construction zone. Wait, I forgot who I’m talking to.

One of the things that we’re trying to do at IBHS is to understand what kind of products can reduce that damage, what kinds of damage modes and severity actually matter… If it’s just superficial damage and doesn’t have to be replaced immediately, that’s fine. If it’s something that is really going to open up the home to potential leaks or other issues in the roof, those are things that need to get dealt with right away.

A small hole in the roof is easy to fix. A small hole in the roof through which boatloads of water pour is still easy to fix, but now everything under the hole needs to be replaced.

And that can take a LOT longer to fix and cost a LOT more money and aggravation.

So we’re trying to understand how those losses can be reduced. From a financial perspective, and also just the sheer headache of going through those practices.

How to do it right: pick a hail-rated roofing shingle

In order to figure out what works best, Tanya’s team has a hail maker and a series of little hail cannons that they aim at their coworkers. Not really, They aim the hail cannons at a test roof to see what happens when they bombard asphalt shingles with hailstones.

If their co-workers happen to be on that roof…

We recently created a brand new test standard to test the performance of asphalt shingles when subjected to hailstones that are very realistic that we produce in a lab—based on tons of data that we’ve collected out in the field on real hailstones.

The test method focuses on the kind of ice that we produce, whether it’s hard or soft—I mentioned previously that that matters in terms of the damage—but the text method also quantifies the damage; it’s not a binary pass/fail kind of test. We actually use metrics to evaluate how severe the dents are, how severe the cracks are, and how severe the granule loss is.

All of those things matter in terms of a good-performing product.

After they do the fun part, they do the boring part: quantifying the damage to grade the shingles.

So in order to do this right and give yourself the best chance to try to resist hail damage, you want to choose a roofing product that has an impact resistance rating and, even more specifically, one that earned a “Good” or “Excellent” performance rating in the new IBHS performance rating scale.

You can find that at ibhs.org/hail/shingle-performance-ratings

In addition, beyond just the roof cover, our fortified high wind and hail program requires the use of one of those “good” or “excellent” rated products and has a couple of other things to help keep the roof in good condition.

Sealing the roof deck with flashing tape, fortifying the edges, and bumping up the nailing schedule. You can find these details on protradecraft.com.

…and those will generally help you out up to about two-inch-sized hailstones. Once you start getting into the three and four-inch things, you’re starting to talk about puncturing the roof deck. There are not a lot of roofing covers that can stand up to that, but the vast majority of hailstorm events are in that “less-than-two-inch” category.

We can make a big difference in the damage by choosing those high-rated products.

Shingle ratings for major brands are published on IBHS’s website, and I’ll also put the chart on the protradecraft page associated with this podcast episode.

All of the products that we tested and published results for on our website were all rated to get a certain classification—class 4 rating—under existing test methods.

What we found is that they didn’t all perform the same, which is why we have certain products that are rated “Good” and “Excellent.”

So really look carefully to make sure you’ve got one of the “Good” or “Excellent” products for the best chance to get a hail-resistant or impact-resistant roof covering.

To sum it up, wine glasses and bowling balls are a bad mix, and going a little above and beyond in shingle choice and construction detailing can pay big dividends.

Remember, you get paid for what you do and what you know.

Now you know more about what more to do.

I’d like to thank the Insurance Institute for Business and Home Safety for lending us Tanya Brown-Giammanco to fill in the gaps in our knowledge pile.

 

—7 Minutes of BS is a production of the SGC Horizon media network.