Reinforce Roof Against Falling Trees?

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I agree. As I said previously, I can see addition roof connectors helping in the case where you're near the edge of the tornado path. But if you're directly in the path, it pretty much destroys the whole structure, roof and all. I suppose you could find some cases where it could have helped, where there is a house or two, that for whatever reason was spared. And if that house had the extra connectors, which is certainly a good idea for any areas prone to extreme storms, then it could help that house survive with it's roof intact. But in my view, that's the exceptional case.

I haven't followed this closely, but I heard reports around the time it happened that said the upper floors were added, perhaps illegally. That has happened before, I remember a dept store in Japan, for example, where they just added a floor without properly considering the additional loads put on the rest of the structure.
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On Wed, 8 May 2013 05:48:53 -0700 (PDT), " snipped-for-privacy@optonline.net"

Florida just bumped up the wind code requirement in this area to 170 MPH. That certainly starts getting you up into the F-3 tornado category. The connector requirements tie the roof, all the way down to the foundation as a continuous system.
I did see what happens when a tornado overcomes this system. The trusses actually broke where the clips held them and the top chords went off in 3 pieces. The reinforced concrete block walls held. One of the occupants was leaving through the open roof when her hubby grabbed her ankles and they both came down and balled up until it passed. Her hair was instant "buck wheat" style with hundreds of tiny braids in it.
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On May 8, 11:44 am, snipped-for-privacy@aol.com wrote:

I'm sure you'd agree the speed of the wind is only one factor. The winds you'd see in a hurricane are straightline for the most part. With a tornado, they are strongly rotational. Also, with a tornado, you not only have high winds, but a very localized low pressure, vacuuming effect that pulls stuff apart. That force on a large roof area could be more destructive than the wind speed. In fact, that is probably what happens in many cases, isn't it? That the roof is essentially sucked off, not blown off?

Yep. If the rest of the house isn't tied to the foundation, then having the roof stay on could just mean the whole house comes up and gets destroyed anyway.
I agree that it's a good idea to have the increased tie-downs. Especially since with new construction, the added cost is minimal. I just don't think in the case of a tornado, if the house is directly in the path of an F3+, it's probably not going to make a difference, in most cases. The farther you are away from the center, then obviously the chances of it making a difference that avoids total destruciton increases a lot.
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On Wed, 8 May 2013 09:42:15 -0700 (PDT), " snipped-for-privacy@optonline.net"

Ron White sums it up well. "It is not that the wind is blowing, it is WHAT the wind is blowing. A lot of our codes address minimizing wind borne debris as much as anything., That is why we have the same code for sheds and garages as we have for the house.
The biggest problem with the suction/pressure issue is when the building envelope is penetrated. That is what the impact rated windows or shutters are all about. Once high pressure air enters and you have the lower pressures on the roof or other side, forces are increased. Once the destruction gets started, it proceeds pretty fast throughout the structure. The more you lose, the more you lose.

area and a lot more houses Florida seems to be thinking they have dealt with the wind and they are starting to look at the water. Other than elevation, there is really not much you can do. When we added on to our house I had water in mind. I have no drywall below the ceiling, all plaster or stucco over block, ceramic tile floors, the electric comes down from above and it is a wet location wiring method. I may be replacing devices but I won't have the wiring to worry about. I can hose the salt water out of the boxes, let them dry out and put in new receptacles or switches.
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<stuff snipped>

I read in several places that the pressure differential theories about tornadoes and open windows are mostly myth and that the impact-rated glass is mostly to prevent flying glass shard and other debris-related injuries.
http://www.spc.noaa.gov/faq/tornado/safety.html says:
<<Flying debris is the greatest danger in tornadoes; so store protective coverings (e.g., mattress, sleeping bags, thick blankets, etc) in or next to your shelter space, ready to use on a few seconds' notice . . . Forget about the old notion of opening windows to equalize pressure; the tornado will blast open the windows for you! >>
http://www.accuweather.com/en/weather-news/top-five-tornado-myths-debunke/61918
says: <<Similarly, Americans have held on to various other myths causing them to act dangerously and incorrectly in the face of a volatile tornado. 1. Opening windows during a tornado will relieve pressure and save a house from destruction
Opening windows during a tornado provides no benefits. Though tornadoes are caused by intense pressure, merely opening windows will not alleviate or equalize this. Because of the intense power of a tornado, it is best to seek shelter underground in a basement, or in a room with no windows altogether. Opening them only creates a portal through which more debris can enter your home.>> So I am not sure what bottom line is about internal and external air pressure. It does seem that impact rated windows are very useful in keeping flying debris OUT of a house. The great tidal wave that struck Bander Aceh a while back spared some buildings that had open first floors (allowing debris to pass under the main structure). It also spared some buildings that were parallel to the flow of the debris-laden water. The latter presented a much smaller target for water-borne debris than buildings that got hit broadside with the tidal wave.
--
Bobby G.



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Attn.: Original Poster I noted that you said (in an earlier post) that you weren't trying to save your house; you merely wanted to strengthen your roof in order to keep the roof (and the rest of the house) from collapsing on you before you could get out of the house.
I know some folks in "timber country" who had much the same goal. They stripped the sheet rock off of the ceiling and the two walls that supported the ceiling joists in their bedroom and then reinforced the two walls that supported their ceiling joists by installing an additional wall stud (a 4x4) midway between each pair of existing wall studs. Also, they went into their crawl-space and added support (additional framing with piers) for the two walls that supported the ceiling joists.
They then sistered a ceiling joist to each of the existing ceiling joists and installed an additional a double ceiling joist midway between each pair of existing ceiling joists.
After new sheet rock they had a "safe room" that could support the weight of a collapsed house plus the weight of any fallen trees.
I think that this was "over-kill", but I don't sleep in it.
Anyway, I wanted to suggest a method for solving your problem that could be more effective while being cheaper than beefing up the entire roof.
Hope this helps.
--
pilgrim

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The best design I have ever seen that is tornado and tree-proof is a house built into a poured concrete spindle The technique is simple 1) Pour foundation 2) Pour vertical shaft to desired height 3) Build frame and pour into it what will be the roof 4) Raise roof to whatever is going to be floor height 5) Pour floor into frame 6) Raise roof & floor to next floor height 7) Repeat 5) & 6) until desired height is reached 8) Build casing around central shaft, fill with reinforced concrete to support roof and floors.
The tallest I've seen is 3 stories with a widows walk / terrace on the roof.
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On Wed, 8 May 2013 13:50:47 -0500, "Attila Iskander"

I was at a compound of houses and buildings north of Tampa that were about as good as you can get. They were concrete domes built like an inverted swimming pool with rebar on a 1 foot grid and 4-5" of shot crete on it. I am not quite sure what would hurt one of those things.
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<stuff snipped>

Sadly, even after several serious tornadoes, places in "tornado alley" like Moore have done very little to make local houses more tornado resistant:
http://www.nytimes.com/2013/05/22/us/shelter-requirements-resisted-in-tornado-alley.html
<<Construction standards in Moore have been studied extensively. In a 2002 study published in the journal of the American Meteorological Society, Timothy P. Marshal, an engineer in Dallas, suggested that "the quality of new home construction generally was no better than homes built prior to the tornado" in 1999. Few homes built in the town after the storm were secured to their foundations with bolted plates, which greatly increase resistance to storms; instead, most were secured with the same kinds of nails and pins that failed in 1999. Just 6 of 40 new homes had closet-size safe rooms. >>
I have less sympathy now for the Okies that get blown clean to Oz. At least the ones that rejected calls for improved building codes based on claims "it's too expensive" to build a basement. Yet the Feds (you and me and our tax dollars) are expected to help rebuild areas affected by tornadoes and hurricanes. How about not giving any disaster funds for rebuilds that DON'T include basements?
What would it really cost if a large township got together and decided to help underwrite the cost of installing small pre-fab shelters in cities and towns along Tornado Alley? Sounds like the readiest "shovel ready" project around. Tornado shelters are mass-produced in a pre-fab format that just drops into a 10 by 10 by 10 hole. It seems like Californians and earthquakes, mid-westerners are equally ambivalent about their local menace, tornadoes.
--

Bobby G.






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Why is it that you libs immediately want the heavy hand of govt to come cracking down on those that lost their homes? Looking at the total devastation, it's not clear that a basement would have made much difference. In fact, apparently 7 children drowned in the school basement. Oh, and contrary to the sensational headline, the NY Times article actually says that half of the rebuilt homes do have storm shelters.

And how exactly are all the people going to get to these shelters in the ten minutes or so that they have?

Sounds of the libs licking their chops over another govt spending boondoggle. The govt is already broke.
 Tornado shelters are mass-produced in a pre-fab format that just

And in a free country, I say that is there right. If they want to buy one of those shelters, leave them free to choose.
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<stuff snipped>

<I agree. As I said previously, I can see addition roof connectors helping in the case where you're near the edge of the tornado path. But if you're directly in the path, it pretty much destroys the whole structure, roof and all. I suppose you could find some cases where it could have helped, where there is a house or two, that for whatever reason was spared. And if that house had the extra connectors, which is certainly a good idea for any areas prone to extreme storms, then it could help that house survive with it's roof intact. But in my view, that's the exceptional case.>
The tornado that scattered the oak trees like pickup sticks lifted a car 12 stories in the air at the U. of Md. and killed the occupants. Then the tornado followed a path along a small creek bed where it hit the park and then made a bee-line for a Home Depot/shopping center, destroying all the large signs and pulling up the edges of the metal roof in the open garden area. Then the funnel just lifted into the air and it was all over, just like that. Anything "stick built" that was right in the path was destroyed. Once the cone becomes filled with debris it becomes a potent destructive force. IIRC, most victims are killed by the impact of the debris.
It was just a miracle that it followed the creek where there were no houses for most of its trip through my neighborhood. Now that everyone's got a video camera in their cell phones there's always someone getting a picture of a cow, a shed, a car, a tractor's trailer, a roof, a tree, street signs and all sorts of other airborne debris. Someone even had a still photo of the car in mid air, sailing over the 9 story dormitory and crashing down into the parking lot.
The most fascinating pictures I've ever seen of a tornado was from a news chopper flying above the clouds but still close enough to the funnel to film down inside the cone. It was filled with lightning flashes and tons of debris like roof sections, 2 by 4's, trashcans. Then it split into three tornadoes. I can't seem to find it on YouTube, but I've seen the footage shown several times on both the Weather Channel and the Discovery Channel.
It's as popular as the footage of the family that climbed under an overpass and filmed the tornado as it passed directly overhead. That's got to change your life forever. (-: I've heard authorities say not to seek shelter there, but it looked like the only place they would have been able to survive (and did).
As for my only tornado experience (thank God) the destruction lessened further away from the main track but it was still pretty awesome. Standing on the highest vantage point I could find a few days later, the entire area was a sea of blue tarps. Almost every house for a block or two on either side had major roof or tree damage. Storms like that are exceptionally rare around here and I suspect not many of the newer houses had good "Florida code" connections between roof and frame.
I was surprised to learn how many homes have their roofs loosely attached, although that's changing. I was just as surprised when I learned that the Bismarck's huge gun turrets were held on by gravity alone and they just fell off when the ship rolled after sinking. I suppose the designers figured that the tilt angle required to dislodge the turrets meant that it was "game over" anyway when that angle was reached.
One thing I found quite interesting is that weeping willows were still standing (stripped almost completely of leaves, though) while the mighty oaks were all felled. When you drive through a decimated area you realize how inadequate TV and newspaper coverage is in communicating the scope of the damage. I heard that said often about both Katrina and Sandy. Until you're doing a flyover or a drive through the scope doesn't come across. Five blocks east and I would have been going to Oz in the middle of a funnel cloud.

<I haven't followed this closely, but I heard reports around the time it happened that said the upper floors were added, perhaps illegally. That has happened before, I remember a dept store in Japan, for example, where they just added a floor without properly considering the additional loads put on the rest of the structure.>
Yes, I've read that, too. It's a very common occurrence because each floor is just like the one below it in most cases so when you're on a roll . . . Most construction workers aren't really thinking about the extra stress on the floors below. I read another report today that implied the floors may have "pancaked" and when the top floor collapsed it overload the floor below it, etc.
If they went stingy on the rebar, as some reports indicate, it's no surprise. With so many people killed (700+ at least count) at least a few of us are likely wearing clothing sewed by some of the victims of the collapse. If there's anything I hate, it's people who are working hard to make a living getting killed by negligence or criminal activity. People who rob pizza couriers should be castrated. I wonder if a threat like that would make thieving scum think twice? It should.
Overbuilding happened in the very tony Montgomery County, MD and bless their souls, they forced the builder to remove the extra two stories he had illegally added to the building and fined him quite heavily because the extra two floors opened him to dozens of inspection violations. I also think TPTB wanted to send a very strong message that adding unsanctioned floors is a big no-no. If IIRC, he even tried to bribe someone on the county council, deepening his legal troubles. Apparently he got away with it in the beginning because no one measured building heights because the planning department thought that permitting services was doing it. Permitting services did not measure because it believed the planning department had enforcement authority.
--
Bobby G.



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On 5/6/2013 9:26 PM, gregz wrote:

I cut down a perfectly good maple figuring if it ever fell it would cause severe damage to the house.
A friend in Myrtle Beach about 10 years ago had all the big pines removed from around his house. In a hurricane, he figured one could break off and come through the roof like a missile. Cost him $16,000.
If you ever hire a tree cutter, don't pay until they are done. Awful lot of fly-by-nights in that business around here.
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And make sure you understand what the scope of the work is, eg is stump grinding included? A lot of people assume when they hire someone to cut down and remove a tree, it includes grinding the stump. Usually, that's extra...
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On 5/7/2013 4:08 PM, snipped-for-privacy@optonline.net wrote:

Stump grinding caused a one week break in the last job I had done but he wanted paid for the bulk of the work right afterwards. I knew he was not a fly-by-night so I broke my rule.
Job before, I left in stumps as they were not visible from the street. Termites started making great work of them, so I had the house treated and warranted ;)
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Raise your house so it's above the trees. On a budget, find a used underwater drilling platform. Try craigslist.
m
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On Monday, May 6, 2013 5:26:55 PM UTC-4, Nona wrote:

n an area that has occasional hurricanes and even small tornadoes.

ey fall on the house. It is not a realistic option to remove all the trees and bracing all of the trees would result in a spiderweb of wires all over the place that is not a safe or realistic option either.

were killed when a tree fell on their roof.

etal braces? Could we put metal sheathing beneath the plywood? Our goal i s not to make the roof impervious to trees but rather to give us at least a small amount of time to escape the house safely should a heavy tree fall o n the roof.

Sorry but it's just completely impractical. Trees weigh thousands of pound s. Nothing you could build short of many inch thick concrete walls and ste el trusses can stand having thousands of pounds dropped on it.
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wrote:

Line the peak of the roof with plastic Jesuses....
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On 5/6/2013 5:26 PM, Nona wrote:

changes to make the roof safer in the event of severe weather. We live in an area that has occasional hurricanes and even small tornadoes.

diameter x 70 feet? tall) that are gorgeous but certainly dangerous should they fall on the house. It is not a realistic option to remove all the trees and bracing all of the trees would result in a spiderweb of wires all over the place that is not a safe or realistic option either.

trees? I have seen too many news stories during hurricanes where people were killed when a tree fell on their roof.

shingles. Would it help to reinforce the trusses with horizontal or cross metal braces? Could we put metal sheathing beneath the plywood? Our goal is not to make the roof impervious to trees but rather to give us at least a small amount of time to escape the house safely should a heavy tree fall on the roof.

Are these live oaks? If so, they have shallow roots and the larger ones can smash a house, not just the roof. All of the "hundreds of tall oak trees" can't be within striking distance of the house! Clean up the ones that are close, remove branches hanging over the roof, remove dead wood and open them up....properly pruned by an arborist, the leaf mass is open to allow the wind to pass THROUGH, not blow down the entire tree.
During hurricane preparedness in FL, we attended an interesting talk by the local arborist. One feature of live oaks that makes them dangerous is when two trunks grow together...you can see the enclosed bark on the main trunk....these split and fall more easily in wind.
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