Tornado resistant building design

As a Civil Engineer who has watched the destructive forces that wind generates all over the world, I have wondered about the possibility of beating the wind at the game of blowing homes away.
Civil Engineers are taught to research and experiment, not all Civil Engineers do, but I make up for most of my peers, I am fascinated by possibility.
As I see it there are 3 sectors of the community that could use specific design concepts to save property and life.
- Housing
- Commercial
- Government
Each will have priorities different from each other but for the moment I will stick to housing and maybe do separate ones for the others.
HOUSING PRIORITIES
Generally housing is designed to provide shelter and a safe environment for people to live and care for other members of the household.
Potential design issues that are not compatible with disaster design include
- people wanting bigger houses than they need
- where actual cost does not seem to be an issue to get the right look etc
- they want 3 lounge rooms, a bathroom and bedroom per person , inside and outside kitchens, theatre room etc
And they dont want debt!
This discussion cannot help people with that attitude or need.

SOME DESIGN PRINCIPLES NEEDED FOR HIGH WINDS
- House to not blow away
- house to not rattle apart
- windows and doors to stay closed
- occupants are safe
- no flying objects
SOME DESIGN CONCEPTS TO HELP MEET THESE PRONCIPLES
- Foundations designed to anchor house to ground, either by weight, screw or ground anchors.
- structure actually fastened to the foundations with rods or cables from the foundation right through to the top of the roof.
- Door and window frames to be welded steel and storm proof
- Timber or brick walls to have steel sections through them so they are not blown in or out.
- development of understanding as to why and open door or window can destroy a building and steps to deal with that.
- use of bolts rather than nails for structural situations and connections
SOME BASIC REQUIREMENTS
It could be that a community may decide to have some basic requirements for all new housing.
- A storm shelter built into structure that does not look like one, buts acts like one if a wind comes. In this case part of the house may blow away but people are protected and have shelter immeadiatley after the storm.
- maybe basements should be encouraged where they would not fill with water

SOME OBVIOUS POINTS OF CONTENTION
- Insurance companies may require an improved design to save the whole community the expence of rebuilding each time.
- PEOPLE OBJECT TO BUILDING CODES NOW what would they think about these points?
- maybe civic buildings are built to a standard that fits the need.
- limits as to how big a house can be built in particular areas so they can be built to resist a high wind at a reasonable price

The issue of rights and freedoms will no doubt come into it, but my personal opinion is that why should good people have to take risks to help those who dont want to take precautions to help themselves.

Some web sites worth reading
How to resist the powerful winds
Institute of Business and house safety
The hard sell about this web site
"Severe weather disrupts lives, displaces families, and drives financial loss. IBHS delivers top-tier science and translates it into action so we can prevent avoidable suffering, strengthen our homes and businesses, inform the insurance industry, and support thriving communities.
This video shows how good design can make a difference in safety. The house that does not blow away cost $5000 more than the other."
Proving cost is not a great decider of whether to use smart design or no design to save you own home from blowing away
A slightly smaller house could be built at no additional overall cost.

This company claims they have resilient houses do you own extra research please.

I watched that first video, interesting toward the end they said both houses held until they opened the doors. My assumption, logically and based on observation is that is irrelevant. Assuming as I do, that the storm is a powerful one and that it is a direct hit rather than a near miss. A powerful tornado has greater than 100 mph wind and from what I've seen most tornados are accompanied by hail. I researched hardened glass and it was way too expensive for my budget so large hail and debris moving horizontally in 150 mph wind is going to open the windows whether I like it or not.  

In that case for my purposes, I assume that the interior of the house will be exposed to windblown debris. That's why the walls ceiling and door of the mostly underground bathroom are extra reinforced to keep the debris out. I also assume, hope that if the polycarbonate bathroom window breaks that it will not produce dangerous fragments nor allow a large amount of outside material to enter. There is a window because I can't stand a room without one and because I want a second means of egress, just in case.

I think effort to encourage better structural integrity is great as it no doubt reduces harm to people overall as well as reduces economic impacts but general reduction of expense to society just doesn't meet my standards. I guess I'm a little OCD about it. Same with floods as I remember the Ohio River moving into our house one night back in 1963. That was an easy fix though, my house is only about three miles from the river as the crow flies, but the crow also has to fly 450 feet up to get here.

My house was also not all that expensive as it is much smaller than most, nor even compared to others of a similar size. I just spent money on things like epoxy coated rebar instead of things like polished granite countertops.  

I think there's a lot you can do to make your building resilient if a F2 tornado is 300' or 500' from your house.  If a F4 hits your house I don't think there's much that general building practices can do to handle that.  Sure a very dedicated person could build something tough enough for that but it would be at extreme cost.  A F5 tornado leveled the town of Barneveld WI in 1984.  It was .4 miles wide.  

From the US National Weather Service:
F1 Moderate tornado 73-112 mph
The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads; attached garages may be destroyed.

F2 Significant tornado 113-157 mph
Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light object missiles generated.

F3 Severe tornado         158-206 mph
Roof and some walls torn off well constructed houses; trains overturned; most trees in forest uprooted

F4 Devastating tornado 207-260 mph
Well-constructed houses leveled; structures with weak foundations blown off some distance; cars thrown and large missiles generated.

F5 Incredible tornado 261-318 mph
Strong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile sized missiles fly through the air in excess of 100 meters; trees debarked; steel re-inforced concrete structures badly damaged.

I'm convinced that, at ground zero, for a severe tornado, the safest place is underground.  Tornadoes seem to sweep along the ground wiping out things in their path.  I'm not certain, but I've never seen where one penetrated the earth's surface where it touched, or in it's path.  I built my tornado shelter with that in mind.  

As Mike said, I'm certain that a person could build an above ground home that was tornado-proof, but I think the cost would be very high.

This video is remarkable because it talks about the same points I started with.
What are homes for shelter , protection.
What have homes tuned in to, a show of wealth, big enough to store anything etc
But it is thought provocing

Mike, thanks for you input.
I note it mentions either poor foundations or being lifted from foundations.

A critical part of my concept is good foundations, with continuous connection right through to the roof ridge.
Screw ground anchors are drilled up to 30m into the soil until a particular level of resistance is achieved, they are made of steel and are about 12 inches in diameter.
This system is regularly used in poor ground conditions.
Ground anchors are cables dropped down drilled holes and grouted in so a particular minimum pull strength is achieved.
This method is used to stabilise ground in cases where deep basements are installed for multi storied buildings, to hold the walls in place prior to the concrete is in place.
They are both proven methods.
3

This company installs ground Anchors
retaining-wall-techniques/ground-anchors/
And this is how its done.
"Method of execution
The anchor is drilled into the ground using the drilling head.
Jet-boring starts at a depth of around 2.00 m to destress the soil surrounding the anchor, thereby easing the drilling process.
The water jet is transported to the tip through the central opening of the inner rod and flows back to the surface together with the displaced soil.
In order to reach the desired depth, the first anchor rod is drilled in.
Then the next anchor rod is fitted to the first and drilled further into the ground.
This process is repeated until the anchor has reached the desired depth.
Once the right depth has been reached, concrete mortar is injected into the anchor.
This results in an anchoring body that is perfectly aligned with the surrounding soil.
Next, an anchor head is mounted to the retaining wall. IN TORNADO CASES THE CABLE WOULD EXTEND INTO THE FOUNDATION STRUCTURE
The tensile elements are fixed to the anchor head.
This anchor head transfers the pre-stressing force from the anchor to the wall.

I think that video by the designer was thought provoking.  A layer of sheet steel would go a long way towards helping with projectiles.  Not sure about condensation or other effects on the building envelope.

I wonder if you would have to eliminate roof overhangs to prevent the wind from uplifting at the soffit.  

At least by me, foundations go 4+ feet deep and I don't think tornadoes ever suck them out of the ground.  More like they rip the house off of the foundation.  So tying them together would probably be enough.  Especially if the foundation walls were locked into the footing somehow.

Hi,  I have built homes with wood as the foundation and basement walls with the house tied down to the basement. Tamarack, otherwise known as Iron Wood, can be very hard to work with when dry, I had to use methods for building with steel to erect the basement walls. I think this might be the best material for building a small underground shelter.  Going underground has ben a preferred method to try to escape a wind storm or tornado. Yet sometimes the home falls in to the basement. Wind, water, and hail. all have to be guarded against. Very few people think of fire, but broken gas lines or fire from the wood heater are problems as well.

Having an emergency plan in place and practicing it is also preferred.  If neighbors and relatives know the exact spot where you are sheltering, the survival rate goes up if  buried.

Building and acting properly for an emergency should be our best resources for immediate survival of a storm.

Here they use metal straps anchored in concrete to hold down mobile homes and doublewide prefabs. They keep them from blowing away in a near miss, but they still come apart in a direct hit.

I remember a couple in years before and a few since but this is the incident that sparked my interest in tornados and how not to get blown away by one. 1974 super outbreak

I'm pretty sure the map shows just the bigger ones, smaller ones especially if they didn't hit a town didn't make the cut. I think the one in Zenia Ohio is probably most famous as there was little left of that place the next day. I'm in and was then in SE Indiana. Storms started in the afternoon as we got home from school and went on all night. I have never before or since seen such fantastic lightening, for hours I bet, there was never more than a second or two without the sky lighting up.

It was the biggest outbreak ever recorded until again in 2011. One or more of those little ones hit or passed close to my house in 2011 and I got some dents in the truck from hail, nothing more.  I don't know if I was actually hit because, me and the dog were in the bathroom but the old barn across the road was gone when we came out.  It wasn't completely gone, scattered is a more accurate word. I was able to salvage lots of pretty good metal roofing and wood siding, delivered to my yard for free.

I've never been hit by a big one directly, but I've seen them and what they do, guess that's why I'm all freaky about it. In my opinion a decent house should simply shrug off a storm up to at least F2, maybe low end of F3 with little to no damage. After that I'd expect to lose widows and roofing, at high F5 probably the whole upper floor.

And I believe tornado resistance is not cost prohibitive, so long as a person can live without the polished countertops and space for an indoor bowling alley. My screw up was the "cheaper to build up than out" thing. If I had it do over and I hope I do, all 1000 sq feet of living space will be on one floor, all steel reinforced concrete, all partly underground with a couple feet of rocks and soil on the roof.

1974 tornado map

2011 tornado outbreak

At least by me, foundations go 4+ feet deep and I don't think tornadoes ever suck them out of the ground

Mike its really a case of doing the sums and testing, rather than working from gut feeling.
Its a matter of cost as well.
I am familiar with concrete foundations and screw anchors and the labour involved with screw anchors is minimal c.w. digging, forming pouring and finishing concrete.
Still let te designs come out.

Hi John and others,
I grew up in central Iowa--what used to be tornado alley, now apparently it has shifted south and east. My dad, who was an electrician, not a structural engineer, researched this topic in the 70s and decided that an earth-sheltered house was the way to go. We even toured several underground, and partially underground, or just sod, houses in the late 70s and early 80s. He said if he ever built a new home it would be earth-sheltered.  He never did build a new home so we never got to live in one, unfortunately. He favored this style https://www.chicagomag.com/real-estate/april-2020/hobbit-house/  for the midwest it also offered the chance to greatly reduce heating and cooling bills. While he would have considered himself a conversationalist, his main motivation--like most people out there--was economic.

Natural Spaces Domes are tornado resistant. Minimum Tornado resistance is that the design doesn't include "additions/extensions" which would destroy the pure "dome" shape. and depending on and design additional engineering and material choices the design can be all forms of disaster proof--- including tornadoes -

https://naturalspacesdomes.com/

Addionally they can be built far below stand price per square foot of traditional builds.

These aren't permie construction, they discuss basic stud wall commercial home builder houses, but they are interesting information. I read these looking at the physics of why some houses break more easily, and found them educational. All from the same site, if you need an account to see them, this place does not spam you. It's a normal builder site, the Journal of Light Construction (JLC)

Engineer's Assessment of Tornado-Damaged Homes
Wind-Resilient Buildings
A Texas Tornado: Lessons Learned
Practical Engineering: Resisting Tornado Damage

The part I found most educational, not being a fan of that type of building practice, was how much of the problems were caused by sub-standard work, and corner cutting. Most of the solutions to the problems were easy, just not implemented, or done badly.

Log cabins can be resistant to tornado level winds. I think that at some point, like 300mph winds, will destroy most above ground structures, leaving the earth sheltered homes, I believe, with the highest probability of keeping inhabitants safe. I built a log home in 2018-19, and during that time I had a chance to chat with a log home builder who was nearing retirement and had been building log homes for more than three decades. He shared a couple stories with me of tornadoes in Tennessee that severely damaged or removed stick built homes next door to log homes which remained intact. One story he shared had a stick built addition added to an older log home, and the tornado took the addition off the foundation, along with neighboring houses, leaving the log home standing. I believe that stick built homes can be tornado resistant like a log home when specific ties and anchoring is used. I will say it is sad how home building codes, at least here in Tennessee, have been reduced over the last few decades, allowing the use of cheaper materials and also spacing those materials farther apart, all for the purpose of building as low cost as possible to maximize profit. It's no surprise to me how recently built homes can suffer major damage from 80-100mph winds that may only tear shingles off of a roof of 1960's era construction. While my log home hasn't been hit by a tornado, it did go through a derecho in October 2019 that garnered national headlines. It threw my grill off the porch and I lost about ten or so mature trees on the farm, so I was fortunate. Neighbors had shingles torn from roofs and vinyl siding torn from homes, roofs torn off barns, and collapsed barns.

Evidence shows that stick building techniques are an area that needs improvement

Doesn't PDM have some diagrams about means used around the world to protect houses from hurricanes?  Yes, different storms, but still deals with high winds.  From what I recall, the main point of the design was using plants (trees and bamboo) as a way of lifting high winds over the house.  I believe the wind plantings were themselves placed on a berm to amplify that effect.  Houses were still anchored and well braced, etc.

Yep, looked it up, see pg 267.

Monolithic Dome Institute in TX teaches people how to build the strongest (and most energy efficient) homes I'm aware of, but they have a few issues:
1) Cost of the equipment
2) The unconventional appearance of the buildings
3) The difficulty of modifying the structure when needed
4) The use of materials which are not recycled

I have helped build two of these using their methods, and developed my own methods which solve the issues listed above

Dave Pennington wrote:I have helped build two of these using their methods, and developed my own methods which solve the issues listed above

I'd encourage you to share those methods.  Either here or in a new thread.  Sounds cool!

Melissa, I think you dad was right, in all aspects.
Maybe you could build one/ They are a lot i of work.
Brian, what is a

    it did go through a derecho

It is interesting to hear these concepts discussed.  I worked in a federal building science program, so would like to provide some thoughts.
The concept of structurally tying a building from peak to foundation is called continuous load path.  The forces are directed into a solid foundation.  
Window protection can be achieved in a couple of ways.  I like the concept of structural shutters.  These can be sliding or hinged, although I expect a sliding system would likely exceed the maximum strength of a hinged one.  It is not all that difficult to develop decorative upper and lower slides within which the shutters can move in and out or up and down.  Add aluminum foil and they will also reduce radiated heat during hot spells and wildfire incidents.  There is no reason why a decorative (and potentially sacrificial) overlay could not be placed over a metal grid.  Another method to protect windows would be hurricane netting of kevlar/aramid materials.  I like to design my netting to have some space over the glazing to ensure room for deflection if hit by debris.  Netting could be designed to deploy over a smaller structure to allow wind forces to be directed into the anchors for the net.  By itself, netting breaks wind/structure interface surfaces and reduces transmitted force to a significant degree.  There are hurricane nets that have passed Miami-Dade 200 mph hurricane requirements.  That would cover the most common tornado wind speeds.

There is a clear benefit-cost ratio that says that protecting against tornado wind speeds up to 200 mph will protect the vast majority of structures.
I saw someone share the old Fujita scale.  As of 2007, the National Weather Service switched to the Enhanced Fujita scale.  https://www.weather.gov/oun/efscale

EF SCALE  EF Rating 3 Second Gust (mph)
0 65-85
1 86-110
2 111-135
3 136-165
4 166-200
5 Over 200
As can be seen, protecting to around 200 mph provides protection against all but the strongest tornadic forces,  That leaves 0.1 percent for the EF-5 tornados.  That said, EF-5s produce roughly 20 percent of the tornado deaths.

One modern building technique that weakens structures is the truss roof construction method.  If used in a gable structure, a weakness is developed at the base of the peak along the wall.  There is insufficient strength in the roof membrane to support the end peak areas.  It is suggested that that be mitigated by placing 2 x 6 or larger lumber across multiple rafters to allow the system to be stiffened against the wind.

One of the new energy efficient methods uses a wider spacing (24" vs 16" on center) but with 2 x 6 studs to allow more insulation placement in outer walls.  Any large openings must be reinforced to assist in carrying the load from peak to foundation.  Speaking of foundations, if one is in an earthquake prone area, it is a very good idea to check geologic maps for soils prone to liquifaction.  During an earthquake, some clay/silt soils will literally liquify and loose much of their ability to carry a structure.  This is very seldom seen over a large area, so damage to structures, especially unreinforced masonry is very likely.  It does little good to build a shelter in an area that may see loss of soil support.  While tornadoes do not generally dig very deep, they have been seen to remove the pavement from a road.  It helps that they are usually moving forward at a good clip of at least 40 mph.

Large overhangs are not good with wind, but they provide more consistent protection from sun.  Perhaps it is useful to build with a structural break from porch to building, but remember that any lost portions of structure create debris for both you and your neighbors.  I have a design concept in my head that one could create a solar roof (passive protection or solar power) that could be dropped in case of high winds and fastened to the side of the structure to provide an extra layer of protection.  Just a thought.  I would hate to see solar panels open to debris, but since wind speed is lower on the ground than above it, the actual speed of debris impacts might reduce.  It certainly would reduce the potential that a neighbor might find your panels in their back yard.

Richard, I love this expression

The concept of structurally tying a building from peak to foundation is called continuous load path.

But can you explain this bit again please?

One modern building technique that weakens structures is the truss roof construction method.  If used in a gable structure, a weakness is developed at the base of the peak along the wall.  There is insufficient strength in the roof membrane to support the end peak areas.  It is suggested that that be mitigated by placing 2 x 6 or larger lumber across multiple rafters to allow the system to be stiffened against the wind.

I think we can build better for wind resistance ... not so sure we can build better for tornado resistance, unless you are really saying something like  EF-1 or less (low winds, weak tornado) resistance only. In other words, build as best you can to improve the resistance of your home to local conditions, including straightline winds, but build a *safe room or underground shelter* if you want to survive a tornado hit.

In the Joplin, MO. tornado with winds from EF-3 to EF-5 speeds, tornadic wind actions vs straightline, and debris action, no building construction types (residential or commercial) saved folks ... the building itself didn't survive; if there was a death, there was building failure. No building codes saved people, although this could possibly be blamed on the lack of a true tornado-type building code. No safe rooms and such existed in the tornado path, where folks died. 161 deaths, but little action since then on *preventing deaths*, whereas safe rooms or underground shelters are well-known ... 2 billion dollars in damage, and lots of talk and action about how to prevent *that*.

Perhaps what saved most folks in Joplin was the herd mentality ... "it will happen to someone else ... it won't happen to me". And it did for tornados ... if you didn't do anything (you didn't build a safe room or underground shelter), the odds are that you survived. 20k people total in Joplin, 161 dead ... less than one percent. WRT tornados, another herd mentality characteristic is to ignore warnings, because most of the time, a tornado doesn't happen, or it happens elsewhere ... unlike hurricanes, which are more visible to everyone, and mostly accurate in predictions if not always in intensity.

Given that you can mostly avoid hurricanes, wildfires, and similar events, and given that you can't easily avoid tornados, safe rooms/underground-shelters seem to be the only thing that should get attention, over and above anything else, if we truly want to save lives. If I read things right, FEMA may help you with safe room costs ... but, this is still "action at the individual level"; you have to get educated on this, and then help yourself. The herd won't change, or changes so slowly that there are probably many more Joplins in our future (and Katrinas, and wildfires, and ...)

Back to building codes (and why some of us have problems with them) ... we have a curious thing that occurs in the USA ... a million different ways to do one thing, with little to no common best practices effort. This happens in politics, public schools, building codes, anything ... you name it, we tend not to do best practices in it ... we tend to do things "locally" ... and, we tend to favor that over best practices. We have 50 states, each of which does their own thing; we have hundreds of local municipalities, each of which does their own thing. And finally, we have millions of governmental employees, each of whom do their own interpretation of the rules and then do their own thing to apply the rules.

You could call a building code a best practice, except codes are mostly defined by industry and governments, not by people ... the same folks that builds things and taxes things at the herd level; codes are accepted at wildly varying levels by localities; codes are not freely available to people in all mediums.  This fits for the herd who is buying a home ... not for the individual who wants to do something different, or with something experimental ... so it is only certain individuals who chafe under the building codes. The herd is buying tract homes left and right. The best advice I ever got for building codes (as an individual who wanted something different on my homestead) was "build to the best of your abilities, but change to everything that the *local* inspector wants *during* an inspection, regardless of what you think, if you want to pass the building inspection".

My spin on this for experimental things is "do it their way first, and then do it my way after, to implement a best practice that I want, but the locality doesn't understand or want." The corollary to this is "choose your locality wisely." Even more personally, building codes seem to stifle creativity, which perhaps limits more potential best practices, and thus tract homes win out again.

All of these subjects are tough things to wrap your head around ... lots of reading to do ...

Jt Lamb - It is totally possible to build to provide safe haven for people who want/have to shelter in their homes.  It is easy? - NO.  Is it cheap? - Not always.  Each builder must make decisions based on far more than natural hazard risks.

EF-5 tornadoes are the most destructive and dangerous, but make up about 1 percent of the tornadoes each year.  Each building project is a crap shoot with respect to whether or not a tornado will impact the site.  In Mayfield, KY, there was a massive Methodist church built of stone, concrete, steel and wood - it lasted over 100 years before an EF-3 totaled it.  In general, one is far less likely to experience a direct hit by a large tornado than to be impacted by a hurricane along the coast or a wildfire if you live in the forests.  I can provide a laundry list of how to reduce risk from wildfire and all other natural hazards.  As an earth scientist/hydrologist/engineer over more than half a century, I have seen impacts by almost all natural hazards.  I have worked with some of the best and brightest experts on construction methods related to wind, fire, flood and earthquake.  This in response to tornado, hurricane, floods, earthquake and wildfire.  In many cases, multiple hazards combined in one mass impact.

Hurricanes impact very specific sections of the coast.  Even with the much larger area of impact, it has been very difficult to determine the probability of a direct strike within 50 miles.  I know because I have had conversations with hurricane specialists from NOAA on that exact subject.  

Wildfires impact specific areas and follow clear natural guidelines.  It is foolish and tempting fate to build a home next to 70 to 89 foot trees, but I have seen that while working wildfires in CA.  

Building codes are intended to reduce stupid.  Building codes cannot overrule laziness nor criminal behavior.  Residential building codes are considered proscriptive - many codes departments interpret that as "Do it exactly as the code is written."  They do not want to have the responsibility of determining if a builder is actually exceeding that code by using a "non-conventional material/method".  Commercial building codes set guidelines for performance and architects/engineers are required to ensure their designs meet or exceed those codes.  

FEMA almost never pays for individual storm shelters although they provide plans and books showing best practices.  They do often provide for construction of community shelters although I heard one team after they inspected one community shelter only to find that the lock was placed on the outside of the doors and the one to unlock those doors had to remain at risk.  Like I said, hard to fix stupid.

Each person must take responsibility for their decisions for wherever they live.  I was fortunate.  I grew up on a farm in a rural area where tornadoes seem to travel just north of me if they do travel.  I rode out Hurricane Hazel in 1954 in an old farmhouse that has a primary vulnerability to other wind impacts.  We saw no damage from Hazel even though it has the distinction of being one of very few hurricanes to make it to Quebec as a hurricane.  I am not in an earthquake zone, but the mass of my foundations and the sub-strata reduce impacts of earthquake.  I maintain a couple of hundred feet of defensible space for wildfire even though no one thinks it could happen here - I do not believe the area to be impervious to wildfire.  I have emergency generators to reduce impact of power outages from almost any source ( - almost because I do not have sufficient information as to actual risk of nuclear electromagnetic forces).

It should be noted that the government (less the military) does not have millions of bureaucrats and very few of those have the capability of setting their own interpretation of the rules they must enforce.  I always attempted to be responsive to all, even those who just wished to complain and not actually do anything.  I worked for a federal agency that is clearly imperfect (no plan by humans ever is perfect), but the rank and file were among the most dedicated and caring people I would ever hope to meet.  Most of those so-called faceless bureaucrats actually care about their jobs and the American people they serve.  A few will always poison the well, but by and large, over 26 years of federal service across this country gave me hope.  Some of us still consider the term "Public Servant" an honorable one.

And here I thought I was adding to the debate, and not just pushing hot buttons ... maybe 100 or so deaths per year from tornados (normal years, and 500 in other years) should be ignored, as the odds are it just won't happen to any one of us (herd mentality?). But then, why do we have safe rooms and such technology? I'd also point out that these can have stacked functions, and are worthy from that standpoint alone ...

I lived in reasonable proximity to Jarrell, and can't count the number of storms/fronts that I've lived through, while in north Austin, sweating bullets that my family wouldn't be wiped out, with no way to protect them. My FIL's home was wiped off its foundation due to a tornado inside of hurricane Katrina. All of this became enough for me, and I stopped playing the odds and did something about it ...

Didn't say you couldn't build better (for many wind conditions), but a safe room or underground shelter is about the only way to *survive* a tornado in its path of destruction, regardless of whether or not one plays the odds; such shelters are *the* way to make sure you survive, whether you got hit by an EF-2 or larger, or shoddy construction that collapsed around you. No argument on the odds of a direct hit, by tornado, hurricane, wildfire, etc. But if you want to survive a tornado, as in "not get killed" (vs avoiding the other two disasters by getting out of their path), only a safe room or underground shelter will pull that off; read the NIST report on Joplin to see why I worded it the way I did.

Didn't say "millions of *bureaucrats*, just millions in all forms of government, from local to state to federal, and many other areas to boot; each "interprets", and you have to deal with that interpretation as an individual. We are all human, and we'll both read the same thing and come up with two different interpretations; simple human nature. There are plenty of rules/regulations, but no boards of common sense applying these rules, only (strict) interpretation.

Didn't say that building codes aren't good for society, but I did point out why building codes hard to live with in items I mentioned: different interpretations across all localities, playing it safe to "avoid liability" in their interpretations, no free/easy access to code materials, and more. I'd agree that building codes are intended to fix "stupid" (whether interpreting stupid as applied to builders or individuals); on the other hand, the codes implement "stupid" themselves in that they have unintended consequences, and are inflexible.

Didn't say common sense shouldn't be applied wrt hurricanes and wildfires ... no argument on me from anything common sense. But I didn't argue for a "no common sense" approach, like building with cardboard too close to the coast, or not mitigating the trees (or any fuels) in a WUI. Mitigate for these two things (which we've done for wildfires), and get out in advance ... this does save lives, in contrast to what can be done for a tornado.

Didn't say that FEMA will build your safe room for you (or even fully fund it), only that there is some scheme of FEMA assistance, from the little I've read about it. Apparently (with more reading now), they do provide residential "safe room" funding ... to the states, who then turn around and parcel it out to the effort for adding/building a residential safe room ... not that there could be *any* red tape in that approach.

I do not know how to solve the problem of millions of families living in millions of "crap" tract housing that is out there today, in terms of tornados; I do know *how* these tract homes were, and in many cases, still are built, as I spent a decade working for architects/engineers in the building industry ... these homes will have a long-running footprint (be on the ground for a long time), so my guess is that only a safe room can be retrofitted into them. Through that decade of experience, I learned not to buy (a tract home), but to build ...

As a tornado's path of destruction can't be mitigated for, or avoided, as best I can tell, if one is worried at all about their family surviving in the event of a tornado, a safe room is really the only answer. The phrase "have and not need, vs need and not have" is very apt for tornados, on top of which, the stacked function possibilities should help.

Hope this clarifies things, and not muddies them further ...

Listen fellas, we have gone way off topic.
We all know about the damage.
We all know the current situation is hopeless.
We all have personal reasons why its bad.
I am only interested in potential improvements, not a history lesson.

We are essentially on the same page here.  I never stated nor accepted that any number of deaths from any natural hazard are acceptable.  They are not.  How do we get to near zero?

FEMA is designed to support not supplant each State's systems.  That is why no real aid for reconstruction goes to individuals.  The State has that responsibility as well as determining what the "best bang for the dollar" may be for that State.  If your particular flavor of disaster does not meet State priorities, good luck.  

Joplin, MI was a major hit with an EF-5 monster.  Such events are hard to predict, harder to withstand.  Oklahoma suffered a similar outbreak some decades ago and the State provided funding from FEMA for individual shelters.  That has saved countless lives and has reduced anxiety for far more.  A lot depends on the local/state government.  Do they bury their heads in "it can't happen again", "We will force people from their homes" or "It is too expensive"?  Or, do they step up and work with those rebuilding to develop equitable funding programs and clear direction to ensure fighting one type of disaster does not create more risk from another type?  Wildfires are a major culprit here as they often drive flood risks up exponentially.  Tornadoes are problematic with respect to localized flooding.  tornado shelters are no good if local flooding fills them before or during an event.  Even damp shelters can harbor dangerous molds.

Often the best source for funding of shelters or better construction methods/materials is through Small Business Administration loans.  SBA can restructure existing loans to add mitigation to a structure damaged by a natural disaster.  This will be the least expensive way for those who can afford a loan to improve their chances against the next disaster.

The issue of tract or inexpensive housing is an epidemic that grows in potential each year.  Much inexpensive housing is occupied by disenfranchised, minority and disabled populations.  Social inequity has been built into the system and that system is built on the laws passed in Congress.  Local officials look at tax base.  For that reason, they often support rebuilding, many times with lower restrictions.  An example is not requiring the fees for building permits.  This often leads to people, just trying to get their lives back, thinking they do not need a building permit at all or that they do not need to meet minimum codes.  All too often rebuilding on vulnerable areas is hurried, subject to cost cutting, especially on more robust structure materials/methods and therefore builds a weaker future.  Next time, the occupants of those homes may suffer more, some possibly by lives or family or the home.

It took the horror of Hurricane Andrew to kick Housing and Urban Development into accepting that no deaths are acceptable.  In 1994, after Andrew, HUD enacted new regulations creating three classes of manufactured housing (minor bickering about terminology, since HUD was given responsibility for manufactured housing in 1977, there have been no "trailers or mobile homes" constructed in the U.S.  That is what one will hear from the sales staff of manufactured housing lots.  They tell their customers that there are no mobile homes (best story about how that name arose was that a mechanic in Mobile, AL saw a need for rapid, inexpensive housing after WWII and started building them.  Others jumped on the bandwagon in the area when they saw him making money and so, most Mobile homes were originally from Mobile, AL - for what it is worth.  HUD developed manufactured home specifications (no alterations generally allowed and no local standards applied to the structure) for three wind zones.  70-, 100- and 110-mph fastest mile wind speed.  Pay attention to this next section.  Since HUD is stiff, they do not use the same wind speeds as NOAA, they use the older fastest mile standard, or how much time it takes a wind to cover one mile.  This is different than the NOAA fastest 3-second gust ratings.  In actuality, it generally takes a structural engineer to determine how to translate those values as the older fastest mile standard produces higher wind pressures.  Suffice it to say that FEMA purchases only type 3 manufactured housing for placement after any disaster.  Cannot say the same for any RV placements as those are generally just bought off the nearest dealer lots to reduce time for folks to be out of their homes or reasonable facsimile thereof.  Rural areas have very few ready to build housing areas for a number of reasons, the most likely being, it's rural.

So, there is terminology that requires an expert being thrown at potential buyers.  I found a "fun" example (NOT!) in WV one time where manufactured home owners were being told they had flood insurance built into their payments.  What they were not told, was that insurance covered only the unit as purchased off the lot and generally it covered only replacement value with proration - real good insurance - for the dealers carrying the paper.

Since I am beating on the manufactured home market here, might as well throw a couple of additional rocks at the windows.  In years past, local officials generally believed that, since HUD only could determine how a manufactured housing unit (single-double- or triple-wide) was constructed, they had no authority.  That has changed.  HUD now has codes for placement in flood zones (nothing for other hazards beyond wind type and possibly earthquake, but a start).  Any state has to implement foundation codes equal to or exceeding HUD codes in flood plains.  That said, the most common mistake owners make is expecting that those codes are good indefinitely.  Owners tack additions and porch roofs and lanais etc. to their manufactured home.  That action destroys any warranty from the manufacturer unless there are specific areas where a limited number of such additions may be added.  Not all manufactured homes are designed for porches, additions, etc.  Many local officials are not fully aware of the restrictions.  

Foundations:  Manufactured home foundations are often piers with anchors and straps to hold the structure down, creating a continuous load path.  That works in limited situation.  I designed and ran an inspection program after a series of hurricanes.  We found all sorts of issues.  Sites were in old agricultural land which increased corrosion;  contractors after placement often went down the chassis cutting anchor straps to make placement of their work easier (almost never fixing the damage); Electrical contractors took the easy way out and grounded to the chassis or metal of the manufactured home, creating a circuit though the anchor straps - note that current flow really ramps of corrosion forces.  Most people can jog at 5 mph or better.  Building scientists hold that flood flow above 5 mph leads to major forces and potential erosion.

So many details.

As stated before, builders must take responsibility by looking at their sites.  Check before buying, ensure you have a checklist of most common local hazards (let's face it, how many people worry about sink holes in FL?)  Determine how you can leverage mitigation methods to cover more than one type of hazard.  Some mitigation methods are as simple as good housekeeping with low levels of wind-borne debris around a homestead.  Some more complex - how many folks thought the fuse-plug levee on the Ohio would be blown up by the USACE, flooding thousands of acres of cropland to save a community?  It was designed for that eventuality - could a similar one impact your homestead?  Dams along the Missouri were dumped one after another a few years back.  Community buildings including a jail were sited on an island in the middle of the river - not the best planning.

Interesting reading and also noting how little has changed in 35 years.  In college(35 years ago roughly) I was reading some magazine  that the article was discussing about tornado resistant homes and they had a project that something like 50 homes in the worst of the tornado belt were being built with minor changes to resist tornadoes in hopes of eventually testing the changes in real world conditions.

Sounds like many of the things suggested then are still on the to do list / we should try it some day list for today's builds.  I don't remember all of the stuff but here is some of what i remember

Anchoring the whole way up is one.  They were suggesting 3 systems be tried for this.
1. carrying the foundation anchor bolts the whole way to the trusses using steel rod ties and turn buckles to tighten them.
2. for slab floors warping a series of sheet metal bands clear around the house with the band actually poured under the slab.  It went up thru slots in the roofing so it didn't have to go out to the gables
3.  and the one I don't see mentioned here in any form was simply gluing all structural sheeting to the stud, headers, sill plates etc.  They were also staggering the sheets across gable ends  so there was not a line that was a weak link.  There was a special plate that went over the sill to transfer the anchor bolts hold solidly to the wall and by running some of the sheeting clear up to the trusses and adding blocking glued in too the sheeting was actually being used to anchor the roof.

One of the other ones in the changes was they wanted to get rid of gable end style on roofs.  Apparently they were a weak link then.  So the roofs that sloped all 4 ways was their preferred answer.  There was some discussion on cross bracing gable end roof trusses.  I didn't even get it back then.  A 60 minutes or 20/20 show on hurricane resistant roof construction a decade later made way more sense of that issue.

Now in the modern world I think the monolithic domes institute stuff for the 3rd world looks like the start of a real cure for a lot of this.  Concrete  inflatable forms built out of Tyvek panels sewn together, fibercrete with basalt roving layers for primary structure.  Wind the roving on so the concrete is held in compression By keeping the concrete relatively thin, keep costs down.  Then add a few additions from modern chemistry,  Lithium silicate densifier inside and out to prevent efflorescence and some spalling and a paint on elastomaric membrace for water proofing on the outside.  Add a layer of spray on closed cell foam for and additional layer of water proofing and bury the structure enough to protect most of it against flying debris like cars.   Permies may easily have their own verison of this in the underground home with primary entrance facing up hill but sheltered by the hill. Just done in wood and rock with the earth part of the roof providing the down pressure to hole the roof on.

The key point in the ability to bury much of the home in earth is that just like a tanks sloped surface can deflect shells the earth roof can absorb damage and deflect big particles like wind thrown cars.  Even if It has dirt for a roof nothing says it is really below ground.

I found this article about cyclones in Northern Australia
A summary of the hazards are listed in it on page 5  and I guess now the issue issue is designing things to prevent the hazards
homeowners-guideto Cyclones

6. LESSONS LEARNED FROM DAMAGE SURVEYS   MY COMMENTS IN CAPITALS
The most common types of damage observed were:
Damage due to failure of rusted fasteners, connector plates, roof battens and other components.- USE ONLY HOT DIPED GALVANISED METAL COMPONENTS
Damage caused by failure of rotten timbers.- USE ONLY STEEL FRAMES
Garage doors being blown in or out.- REDESIGN SOMEHOW
Roofs being blown away in whole or in part.- TIE WHOLE ROOF TO GROUND
Collapse of unreinforced masonry walls.- MANDATE REINFORCEMENT
Damage to inadequately built housing in exposed locations such as hills and sea frontages.- MANDATE IMPROVED DESIGN
Flying debris breaking doors and windows, resulting in further damage from water leakage and strong winds.- STORM DOORS TO BE USED
Doors and windows blown open due to inadequate fixing to walls or inadequate locks and door sets.- IMPROVE DESIGN
Damage to ceilings and walls due to water ingress through the roof, doors, windows, vents, etc. DESIGN TO PREVENT
Failure of attachments such as guttering, fascias and eaves.- REDESIGN THINGS
Damage caused by falling trees. - LEARN TO LIVE WITH THEM, NO NEED TO LIVE ON A TREELESS PLAIN

It is evident that a house requires regular maintenance and protection to reduce the damaging effect of strong winds that develop during a tropical cyclone.

If people complain about the improved designs, suggest they build a more suitable sized home.
In my opinion most new homes are built as symbols of unexplained wealth on a big mortgage!

Here are a few methods of construction they can help resist.

1. Stagger sheathing 4’ horizontally. Stagger subfloors. Research best patterns for shear.
2. Overlap wall sheathing a minimum of 2’ at all upper floor lines for two story houses, even if they are fully anchored structures.
3. Use as many screws as possible.
4. Use as many hurricane anchors as possible.
5. Avoid soft story conditions and large openings that can’t distribute shear properly. How many times have you seen the classic three wall detached garage?
6. Divide house structure into even squares  with a few interior shear walls with 1/4” gypsum bd on 1/2” wood sheathing (osb or plywood). My contractor had no problem doing this on my house and started doing it on all the new homes he built.
7. Bite the bullet and pay to have over engineered vertical reinforcement at CMU foundations. Overkill on J bolts with oversized washers.
8 Overlap exterior sheathing onto cmu foundation and fasten with concrete screws.
9. Add cross ties and knee walls to poorly built track homes. Overlap the knee walls onto ceiling and roof joists for stiff connections.

Eric, great addition to the discussion.
But what are these please?
"CMU foundations. Overkill on J bolts" and where are J bolts used?


Post 19/02/2022 15:30:52     Subject: Tornado resistant building design

MY QUESTIONS FOR OTHERS TO GET AN UNDERSTANDING ARE IN CAPITALS

1. Stagger sheathing 4’ horizontally. Stagger subfloors. Research best patterns for shear.
WHAT IS THE BENEFIT OF STAGGERING THE SHEETS
2. Overlap wall sheathing a minimum of 2’ at all upper floor lines for two story houses, even if they are fully anchored structures.
THIS IS NOT CLEAR
3. Use as many screws as possible. CAN YOU GIVE AN EXAMPLE, SAY 6 INCH INTERVALS....
4. Use as many hurricane anchors as possible. WHAT ARE THESE AND WHERE DO THEY GO TO?

5. Avoid soft story conditions and large openings that can’t distribute shear properly.  WHAT IS A SOFT STORY?
How many times have you seen the classic three wall detached garage? WHAT HAPPENS TO THESE?
6. Divide house structure into even squares  with a few interior shear walls with 1/4” gypsum bd on 1/2” wood sheathing (osb or plywood). My contractor had no problem doing this on my house and started doing it on all the new homes he built. WHAT IS THE BENEFIT OF THIS?
7. Bite the bullet and pay to have over engineered vertical reinforcement at CMU foundations. Overkill on J bolts with oversized washers. WHAT VERTICAL REINFORCEMENT ARE YOU TALKING ABOUT?
8 Overlap exterior sheathing onto cmu foundation and fasten with concrete screws. O THE OSB IS FASTENED TO THE FOUNDATION ALSO?
9. Add cross ties and knee walls to poorly built track homes.  THIS IS NOT CLEAR, WHAT IS A TRACK HOME?
Overlap the knee walls onto ceiling and roof joists for stiff connections. CAN YOU GIVE US A DRAWING?

John,

I think I know at least part of what Eric Koene was talking about.  My father worked as a computer programmer for a major insurance company and they were always looking for ways to improve the survivability of homes to major storms.  Specifically, they were looking for a type of home construction that could be incorporated into otherwise conventional construction to make it hurricane proof.  Much of this will apply to tornadoes.

The process starts at the foundation where J hooks are sunk into the wall foundation while still wet.  It is a large J hook with the top ending in screw threads facing straight up.   Once the foundation dries and the wall plate is ready to be attached, holes are drilled for the J hook ends to poke through, a large washer is placed over the J hook and a lock washer and nut is solidly attached, firmly locking the sill plate onto the cement wall foundation.  The rest of the wall is built as a normal wall, but each 2x4 or 2x6 is attached to the top/bottom plate by a piece of strapping that is nailed or screwed into cross grain, not end grain so that it really holds if pulled up.  This continues to a second floor if necessary and eventually to the roof trusses which are attached by hurricane clips.  The point is that the whole wall, from roof to foundation is attached by strapping of some sort and the sill is bolted into cement.

Studies showed that houses utterly destroyed by high winds simply lifted up and pulled apart from the weakest joint, usually the roof.  This standard was apparently in place but rarely followed prior to Hurricane Andrew (1991?). An interesting finding was that vast areas of housing were simply erased down to the concrete slab, but occasionally a house remained standing (albeit damaged) in the middle of destruction.  Those houses were inevitably built to this connect-everything-to-the-foundation-with-metal standard.

Food for thought.

Eric

the only way i would feel safe is under a dome. one with the legs and roof extending into the ground for anchor.  anything above ground that catches wind is vulnerable.  the round house vid is interesting though.

Here is southern Illinois I have seen the flashing lights for railroad crossings pulled out of the ground...with concrete attached (1957). I suspect  a deep concrete foundation is at risk as well given the right hit.   There is a video out there of a tornado hitting a car dealer in Marion, Illinois (1982). It looked like every car on the lot is 100 ft or more in the air. I saw the video during safety training I attended back in the 80s.  I have no idea how to locate it  on the net. I suspect much depends on location.  I live in an area where both flooding and tornados are common.  I made a point of selecting a single story house in a potential skip zone on the east side of one of the larger hills in the county.  As long as the storms come in from the West or SW  it should help.

1. Stagger sheathing 4’ horizontally. Stagger subfloors. Research best patterns for shear.
--- Vertical joints between rows of 4' x 8' sheathing should be offset by 4' where possible, to minimize lines of weakness.
2. Overlap wall sheathing a minimum of 2’ at all upper floor lines for two story houses, even if they are fully anchored structures.
--- Horizontal joints between courses of sheathing should overlap the wall-to-floor framing joints as much as possible (up to 2') to help tie the upper floor to the lower floor.
3. Use as many screws as possible.
--- The more screws holding sheathing to framing the better. Whatever standard practice is for a given location, increase the quantity... this is a subjective measure and could mean doubling the quantity. At some point you get diminishing returns on more screws.
4. Use as many hurricane anchors as possible.
--- These are rafter-to-wall or wall-to-sill metal straps, and one at every connection point would probably be best.
5. Avoid soft story conditions and large openings that can’t distribute shear properly. How many times have you seen the classic three wall detached garage?
--- I think this is referring to openings that are very large compared to the wall they are in, so that the wall structure has little shear resistance and could collapse sideways - as in a free-standing garage with one wall almost entirely door opening.
6. Divide house structure into even squares  with a few interior shear walls with 1/4” gypsum bd on 1/2” wood sheathing (osb or plywood). My contractor had no problem doing this on my house and started doing it on all the new homes he built.
--- Add strength to interior walls that are perpendicular to exterior walls, effectively turning the structure into a bunch of connected cubes. This will drastically increase the overall strength as each cube braces its neighbors.
7. Bite the bullet and pay to have over engineered vertical reinforcement at CMU foundations. Overkill on J bolts with oversized washers.
--- CMU (concrete masonry units - blocks) foundation walls can be reinforced with vertical rebar in concrete-filled cores running all the way down to the footings. J-bolts are well described by Eric Hanson. Locating vertical rebar at J-bolt positions where practical will help tie the framing to the foundation, especially if the J-bolt can be set so its hook engages the rebar cage. (Horizontal rebar at least along the top of the foundation with the vertical rebar hooked to hold it down ties the whole foundation together.)
8 Overlap exterior sheathing onto cmu foundation and fasten with concrete screws.
--- Directly fastening the exterior sheathing to the foundation obviously adds strength to the joint, though care has to be taken in moist or termite-infested areas to isolate the wood from concrete with metal flashing so the wood will not rot or be eaten. I think this is a very uncommon practice in most areas, and might be better addressed with good metal bolts and strapping in other than dry climates.
9. Add cross ties and knee walls to poorly built track homes. Overlap the knee walls onto ceiling and roof joists for stiff connections.
--- "Tract" homes are built in mass quantities by a builder, and known for often being of questionable quality. If you have one of these, tying the rafters to the ceiling joists with knee wall framing would significantly increase the overall strength. I would also want to add hurricane ties if not original in order to better connect the whole ceiling/roof assembly to the walls.