How can surveyors tell the difference between high-end EF4 and EF5 damage

[STurner]

I know this is a really hard question to answer but it has left me baffled for many years. How can surveyors tell the difference between high-end EF4 and EF5 damage? On the old fujita scale there were several tornadoes that had swept well-built homes off their foundations and left only the slab and were rated high-end F4, but seemed like they could have been rated F5. I tend to agree with surveyors on being more conservative before giving out the highest rating. Where do they draw the line before deciding on going one way or another? Even some surveyors have stated they were considering an F5 rating but did not for whatever reason. It also seems this way on any tornado at the higher-end of one category and the lower category of the next. It tends to get more complicated though as you get higher on the scale.

 

[Scott Weberpal]

Quality of construction, other damage surrounding the home, distance heavy debris was thrown, etc. etc.

 

[Shane Adams]

It seems that, in the last decade or so since damage assessment has been turned into an art and the F-scale was changed around, it's less about what the tornado did and more about what the builder didn't do.

 

[Rob Wadsworth]

Unified Building Code.
when homes are built to this code, they have standard to judge the wind effects by.
Or so I have read on the NWS site...

 

[Scott Weberpal]

It seems that, in the last decade or so since damage assessment has been turned into an art and the F-scale was changed around, it's less about what the tornado did and more about what the builder didn't do.

If you can be more accurate, why not?

 

[rdale]

Unified Building Code.
when homes are built to this code, they have standard to judge the wind effects by.

Sounds nice in theory - but 1) codes change from location to location and 2) we are meteorologists, not construction experts.

 

[Shane Adams]

If you can be more accurate, why not?

Exactly. I was just making that very observation.

 

[craig buchanan]

2) we are meteorologists, not construction experts.

It has appeared to me over the years that those who deal in extreme weather either get a civil engineering degree or end up getting that level of experience. There could be the very valid argument that for a well rounded met. degree you may need to have some building classes of some kind.

 

[rdale]

Not really - how many met's actually do full fledged surveys? And how often do they do it? If there's a BIG event, they bring in a team with people like Tim. If it's an "ordinary" event, is it really worth it to pay someone another $xx,000 per year to have an engineering degree to determine EF3 or EF4? Nope.

 

[STurner]

Tim M. I believe wrote that some surveyors are reluctant about giving an F5/EF5 rating that it may cause the event to be rated F4/EF4 , even though it may have been deserving of the highest rating. I wonder if it may be a challenge for even some of the top experts to tell you the difference between the two.

 

[Scott Weberpal]

Not really - how many met's actually do full fledged surveys? And how often do they do it? If there's a BIG event, they bring in a team with people like Tim. If it's an "ordinary" event, is it really worth it to pay someone another $xx,000 per year to have an engineering degree to determine EF3 or EF4? Nope.

The original question asked about determining high end EF4/ low end EF5 which would likely bring in experts such as Tim M. and perhaps members or old members of QRT.

 

[rdale]

The original question asked about determining high end EF4/ low end EF5 which would likely bring in experts such as Tim M. and perhaps members or old members of QRT.

Exactly. I'm disagreeing with the comment that meteorologists should get an education in civil engineering as well. I don't think the call for building experts within the met community is that large to require us to dual major in something we'll use 1% of the time at the most. A _large_ percentage of meteorologists will NEVER do a storm survey. So I don't think many hours studying construction practices is the best use of time.

 

[Jason Foster]

So many variables.

There will always be debates about categories of classification for tornadoes, hurricanes and similar weather related events were structures, and lives are affected. There are continuing research, politics, economics, and other factors that go into such assessments. Different people assess different storms, and standards change. I think the thing to remember in classifications as high as (E)F4 or (E)F5 is that both are catastrophic events, and that each tornado has unique circumstances that warranted it's designations. Also remember that there is a certain amount of variability in these assessment give the amount of time, expertise, and data available for evaluating such ratings. There are just so many variables it is nearly impossible to compare one tornado to the next as too why one got a F4 versus another getting an F5.

Now...since I have somewhat of a design background I'll speak to that. Structures come in all kinds of materials, structures, connections, etc. There are different shapes, sizes, designs and more that can significantly change how one structure compares to another. For example....in traditional dwellings in tornado alley you may find a well built farm house made of more modern built materials like pine wood studs, plywood sheathing, vinyl siding and plywood and asphalt shingle roofing. Very common design. Now if was a couple of decades ago it likely won't have the best foundation connects. Probably simple anchor bolts to pier foundations or CMU (block wall) perimeter foundation. They are usually held with a washer and bolt over the "top plate" which is a single 2x6 or larger length of wood. And then simple nailing and old fashion floor truss hangers are used. But in more modern structures built more recently, some homes are adding more anchors like those used in hurricane zones (aka the Dade County Code). These can make a significant change in the appearance of tornado damage after the affect and may not at first glance seem totally justified by the given rating. One of my more famous examples of this was with the (local to me) LaPlata, Maryland tornado that was heavily debated, but in the end it was difference in building types that gave a more confident justification to it's rating.