Wind-Resistant Construction: 7 Minutes of BS (#buildingscience)

March 3, 2020

Wind damage is not restricted to hurricane zones, so why does wind-resistant construction limit itself?

For this episode, we are joined by Dr. Anne Cope, Ph.D, P.E., and Chief Engineer of the Insurance Institute for Business & Home Safety. Anne discusses how wind damage happens, why it matters so much (because usually, wind's +1 is rain), and how to reduce your risk.

"Hurricanes are big named things that we pay attention to. But Mother Nature doesn’t care what you call the wind. The wind blows, and it can destroy things in Ohio the same way it can destroy things in Florida."

Hurricane resistant construction is slightly more resistant than just strong wind-resistant construction, and Anne feels like a lot of people are left feeling complacent because they do not live in a hurricane zone.

"There are plenty of people living in tornado alley who need wind-resistant construction."

What is wind-resistant construction?

wind resistant construction

wind ri-zis-tuh nt  kuhn-struhk-shuhn (n)

The selection of building materials and most importantly, special care in the way those building materials are connected. What you want is for the home or the business to be equipped to handle the forces pof high winds that are going to try to tear it apart.

 

How wind-resistant construction works

Hard wind exerts all kinds of pressures on a house. As it flows around corners, it can create eddies of pressure, sucking and blowing different parts of a building.

"The physics of wind loads are actually a little bit odd. Some of it is counter-intuitive. So the wind is going to try to suck the roof up and off the building. And the wind is going to try to exploit openings to get in and blow the building up like a balloon."

Wind is the push-me-pull-you of the physics kingdom

Because the wind is trying to suck the roof off, the biggest thing for wind resistant construction is to keep the roof down. So that it doesn't fly off like a kite.

So that’s the pull-you part. The push-me relates to windows, doors, and other holes in walls.

Mother Nature is going to try to exploit windows and doors. So if you get a broken window, a broken door, a big garage door that fails, the wind is going to try to get in there and blow the building up like a balloon from the inside. So you want to have a wind-rated garage door, you want to make sure the connections inside the building are strong enough to handle those increased loads in case you get a door that pops open.

Windows and doors are the obvious spots, but gable vents are another. They provide a direct path for strong wind to push that roof from below, while simultaneously tugging on the top.

Large roof vents can definitely be a weak link because they can let in wind and rain…

But that doesn’t mean that roof venting is bad.

Now, you need to have that roof ventilated, but yiu want to choose good products that are going to keep the rain out and that aren’t going to be a vulnerability that they themselves can fly off.

It’s really gable end vents that could be bad news for a house, but the geometry of a gable is suboptimal in a windstorm. 

A hip roof is a better geometrical shape. It’s like a turtle. The wind blows over the top of the turtle…

When the wind stops, the turtle stands up and walks away.

And if you present the wind with a large flat object, like the gable end of a roof...

Putting a sail on a turtle may seem like a good idea in a light breeze, but when that wind picks up, the sail is going to let the wind pick up the turtle and the results will most likely be messy.
Won’t be pretty.

So, back to the venting: hip roofs can be vented using soffit and ridge vents, some ridge vents on the market meet the strict Miami-Dade wind and water requirements, and those products are excellent choices for all parts of North America.

Why wind-resistant construction matters

Because often there is a lot of water being carried by those high winds, and if even a small percentage of the water that hits the house gets is, it can have devastating consequences. 

Wind can really begin the cascade of damage. My family has a personal story on why does it matter?

You know, I hear people say “Oh, well, that’s why I have insurance… that’s gonna pay for my house if it gets destroyed.” or “I’ll just get another house. It’s no big deal, I have insurance.”

I absolutely agree, people should have insurance to cover their risks. But I’ve also seen what happens when you get just a little bit of wind damage. I’ve seen that first-hand. I wouldn’t wish that on anybody. 

My parents had really good insurance during the 2004 hurricane season—and they used it—because their roof failed. They were lucky that the house wasn’t completely destroyed, but the water got in, and so probably 25% of the roof shingles came off, and the water. Came. Pouring. In.

And they spent a year in a tiny FEMA trailer in their driveway and they didn’t get back to normal until the following Christmas. So sure, their house was damaged, but the impact was staggering.

Something like nine bathtubs of water can leak into a house with a few blown-off shingles. So the shingle repair is a few hundred bucks, but the water damage that piggybacks on the wind? It can be financially and emotionally devastating.

How to implement wind-resistant construction and retrofits

Fortunately, keeping the roof down and dry, is a pretty simple engineering situation.

The main things you have to do to get a fortified roof, a good strong roof for your family, you have to do three things. 
  
1/ Nail the roof deck for high winds. You need to make sure it has enough nails, and that those nails are ring-shank nails so they have a good bite.

It should go without saying that the nails should hit the framing, but I’m going to go ahead and say it anyway: The nails should hit the framing.

2/ Seal the roof deck to keep that water out. A lot of roofers prefer a really good thirty-pound felt, double layering that with a good nailing pattern.  

A lot of roofers like the simplicity of a system like the Huber ZIP System because it’s all right there in the manufacturer’s instructions. Some roofers like peel and stick.

There are a few good methods out there for keeping the water out and it makes a big difference. When we have a sealed roof deck, we have shown in our lab, that it prevents 90 percent of the water that tries to get in, from getting in.

The difference between a weekend roof repair and a year in a FEMA trailer. 

3/ Lock the shingles at the lower edge of the roof, so they have the best performance. You have to use the right starter strip, you have to give those bottom shingles the right chance to get past that wind.

Locking the bottom shingles is an important detail.

You put down the underlayment, and then you put the drip edge over the underlayment to lock it down. We also want to see a nice bead of roofing cement—not too thick—to keep everything stuck together, and then use the correct starter strip so that you give that first row of shingles something to bite onto.

That sounds like a great squashed sandwich of roofing material.

That’s a great squashed sandwich of roofing material that’s going to stand up to a high wind gust. And if you do those three things, you’ve got a good strong roof. 

Below the roof, looking at holes in the walls, 

One of the most important things you can do is make sure you have a wind-rated garage door. Your garage door should have a label, it should have a wind rating, and it should be able to stand up to the right wind pressures.

The strength isn’t really a function of, especially strong door panels. They’re buckle-resistant, but really, the wind rating comes from the...

The wind rating comes from the stability of the track and the hardware that keeps that track in place. The panels of the door themselves, you don’t want them to buckle-in and cause a big problem. 

But it's that system together: strong enough panels, good track, and the hardware that connects it to the side, that’s what’s going to keep your door in place and not allow it to just buckle and land on top of your car.

In hurricane areas, it makes sense to use operable storm shutters or impact-resistant windows. Or both, really.

Because of the type of debris that’s going to be flying around, you want to give those openings the best chance of getting broken and allowing that hurricane to come into your house.

If you live in the middle of the country—away from hurricane zones—flying trees may probably seem likely. Unless you’re in tornado alley.

What’s important for your house is that it's connected well. 

Roof to wall connections.

Not just toenailed, you know, they have to actually be strapped—roof trusses to the walls.

And the walls and floor, to the foundation.

The walls have to be connected firmly all the way down to the foundation.

Anchor bolts as specified in the code for the last forever years.

In some places, what I’ve just described is beyond code. And so we are working to make sure that people everywhere have good protection. By talking with building code commissions and building code groups.

Because, again, just because you don’t live in a hurricane zone, doesn’t mean the wind doesn’t want to suck your roof where the sun doesn’t shine. 

The reason why rafter ties may not be in so many jurisdictions could be the colloquial use of the term “hurricane straps.”

Many people have called them hurricane straps. I’d like people to just call ‘em straps.

While it is easy to call them straps or rafter ties, it is hard to retrofit them into an old house. There are some absolutely easy upgrades you can make to existing houses in high-wind areas.

It is absolutely easy to retrofit that garage door.

It is absolutely easy to make sure that when you are reroofing, that you follow those three steps and you get yourself a fortifies roof.

Those are the things that you’ve gotta do when you’re thinking about how to make your house strong.

Strong minds build strong houses, so it’s no wonder that you get paid for what you do and what you know. If you don’t know what you’re doing, it doesn’t matter how well you do it, right? 

Think about that one while I thank Dr. Anne Cope and the Insurance Institute for Business and Home Safety for being a willing participant in our show.

—7 Minutes of BS is a production of the SGC Horizon Media Network


 


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