Jul 7, 2008 10:55 pm US/Central
Home Construction Lessons From Hugo Tornado
(WCCO)
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Time and time again engineer Tim Marshall noticed nails that once held the walls standing straight up. The building code only requires the walls to be straight nailed.
CBS
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Matt Miller sent in this photo of the damage to Hugo, Minn.
Matt Miller
It may seem as if nothing can prepare you for a tornado until you talk to engineer Tim Marshall.
For the last 25 years, Marshall has traveled the country, hired by the federal government to examine how homes react in the worst storms. He's been called in to look at disasters from New Orleans to Parkersburg, Iowa to others right here in Minnesota.
How does one house stay and another get leveled? Is it just that the storm skips over it?
"I find that's not the case. Usually what happens is one house stays because it's a little better anchored than the next house," said Marshall. "The way I look at the house and the way it has failed here it's like links of a chain and where it fails, is its weakest link."
WCCO's Terri Gruca asked Marshall to look at the damage from the May tornado in Hugo. He found lessons that could make us all safer.
"I think the damage would have been less if houses had poured foundations, were bolted properly and had some straps there," he said. "I think they would have some house to go back to."
That's because the wind often lifts the roof off the house or the house off its foundation in some cases causing the entire home to collapse in on itself. These are the things homeowners rarely pay attention to. Face it, we're focused on the size of the rooms, the closet space or the layout of the kitchen but really we should be examining the foundation.
We should pay particular attention to the basement and the attic areas. Just meeting the building code may not be enough to protect you in a storm.
"A building code is a minimum," said Marshall. "That's all it is, is a minimum. It's not a how-to guide on how to build a home."
Marshall compares it to studying for a test.
"What's your goal when you're studying for this test? Is it just to get the minimum, maybe a 70 percent? Or do you try to make your goal a little higher than the minimum?" asked Marshall. "When I studied for an exam when I was going through school I was not content to study just for 70 percent. I wanted to see if I could get an A."
Here's what he means. When you take a look at the remnants of some of the Hugo homes you find pieces of wood still attached to their foundations. That is a code requirement that requires builders to anchor the sill to the foundation using an anchor bolt. However, time and time again Marshall noticed nails that once held the walls standing straight up. The building code only requires the walls to be straight nailed.
"That's the failed area," said Marshall. "The building code basically says you've got to take that wall stud and straight nail it down to the plate. And that's great for gravity load, for the weight of the house down to the foundation, but when you lift it up or push, it pulls right out and it leaves the nails standing straight up just like that."
Metal plates called hurricane straps or ties would help. They can be installed in new or existing homes where the walls meet the floor and up at the roof. Roof straps were adopted into the International Residential Building Code in 2006, but Minnesota chose not to require them even though there's proof these hurricane ties make a big difference in tornadoes too.
"Those two nails are just straight nailed, they fail very easily," said Marshall. "To do this, to pull it right out of the two nails -- 60 to 70 pounds of withdrawal force is all it takes. Where as if it was strapped it would be a 1,000 or 1,200 pounds."
Scott Olmstead Builders demonstrated how easy it is to remove a wall attached with nails only. With the hurricane ties even the crowbar can't break the wall free.
Scott Olmstead Builders started using ties four years ago. The company thinks they're worth going above code. The house they're working to rebuild didn't have them before the tornado hit Hugo.
"It is not required but we put them on because it's a stronger house," said Nick Hinrichs, superintendent for Scott Olmstead Builders.
At 45 cents a piece we're talking a total cost on an average home of just $1,000.
So can you add these to an existing home? Marshall said yes, but it can be an expensive process.
"You can get straps and you yourself can attach the floor joists to the sill plate. That can be done in houses that you can get up in there. You've got to have an unfinished basement," he said. "But if you can get up there, then I would. I've done this in my own home. I've gotten metal straps and I've connected these things together."
"I think it just depends on your level of risk. What do you want? There are a lot of people who say it's not going to happen to me, tornadoes are rare, but I bet if you got to Hugo and talk to people a lot of people would say we never thought we were going to get hit by a tornado," said Marshall.
Tuesday at 10
Marshall's biggest concern after examining the storm damage in Hugo centers around the place we're all told to seek shelter -- the basement. Most of the homes damaged in Hugo had walkout basements built on block, instead of poured cement, foundations.
"I know we're always told to go to our basement when there's a tornado warning issued but that could actually be a deadly decision if you have one of these weak foundations," said Marshall. "The house will literally crush you in your basement."
Marshall suggests homeowners invest in a safe room. A 4 foot by 6 foot room can cost you $7,400. Tuesday night at 10, we'll show you a place in Minnesota that installs them and why they may be the one sure way to keep your family safe.
Gruca has put more information on her blog on how to tell if your home has these safety features or how you can install them in an existing home.
(© MMIX, CBS Broadcasting Inc. All Rights Reserved.)
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