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Information about Engineering &
Florida Wind Codes for Material Packages*
Due to the persistent threat of hurricanes, the
state of Florida has some of the most stringent engineering requirements
for buildings in the country, and, in fact, in the world. Any structure
built in Florida (including simple screen rooms, car ports, etc.) is
subject to meeting these requirements.
What exactly are the state of Florida requirements?
How do I show my structure is capable of meeting those
requirements?
Once you design my structure, then it meets Florida requirements and can
be built anywhere in the state?
How do I find out what wind speed is used in my area?
Is the wind speed in my area all I need for the
engineering?
How do I find out my "exposure factor"?
What exactly does the "exposure factor" do and why is it
important?
How many "exposure factors" are there anyway, and what do
they mean?
Once you have all this information, how exactly is it
used?
With all of the hurricanes in recent years, should I go
beyond what the engineering requires and build a stronger structure?
Is this engineering design all I need to get my building
permit?
What is the difference between generic engineering and
site specific engineering? Which do I need?
When should I get the engineering and apply for a permit?
Why don't they just have
specifications we can follow which will be acceptable?
What exactly are the state of Florida requirements?
In Florida all structures must be shown to be capable of
withstanding the expected maximum winds from a storm. The expected maximum winds
from a storm vary by location. For instance, coastal areas of South Florida have
higher expected winds than inland areas of Central Florida. Note that these
expected maximum winds could be exceeded in any area, but based on statistical
studies, the probability of that occurring is low. Politics also comes into play
in determining an areas maximum expected wind.
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How do I show my structure is capable of meeting those
requirements?
That is where engineering comes in. When we help you
design your structure, we use engineering which meets Florida requirements. The
engineering specifies among other things how the structure must be built, how
pieces must be fastened together, and what size pieces must be used to meet
certain wind conditions.
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Once you design
my structure,
then it meets Florida requirements and can
be built anywhere in the state?
As noted above, Florida has different requirements for
different areas. We can design individual structures to meet the requirements of
almost any particular area within Florida. However, in order for us to do that,
you must provide us the the criteria for your area. For example, most inland
areas of Central Florida use 120 M.P.H. Coastal areas of Central Florida are
likely higher, though. By default we design to 120 M.P.H. since that is the
criteria in our area. (Please note that certain areas of the state like the
Florida Keys and parts of Broward & Miami-Dade may have special requirements not
always covered by our engineering. Our customer base is primarily Central
Florida.)
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How do I find out what wind speed is used in my area?
Contact your local building department. They should have
that information readily available since they use it all the time.
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Is the wind speed in my area all I need for the
engineering?
Usually it is, but not always. In addition to wind speed, there
is also what is known as an "exposure factor". This takes into account how your
property is situated relative to its surroundings. For instance, if you live on
a lake, you will be subject to higher winds than if you are surrounded by
houses. The vast majority of homes are exposure "B" and that is the standard
design criteria. However, if you are not exposure "B" the design has to be
modified accordingly.
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How do I find out my "exposure factor"?
If you live in a typical residential development
surrounded by homes and not on a body of water, then most likely you are
exposure "B". And that is what the vast majority of houses are. If you live on a
body of water, your "exposure factor" may be different. And water is not the
only thing which can change your "exposure factor". In general, determining the
"exposure factor" can be somewhat complicated. You might want to contact your
local building department to see if they can help you. Sometimes the answer is
very straight forward and simple, but sometimes you will have to go through a
step-by-step process involving measurements and calculations to precisely
determine your "exposure factor".
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What exactly does the "exposure factor" do and why is it
important?
The "exposure factor" allows the design to be modified to
meet higher expected wind conditions than the norm. The "exposure factor" is a
mandatory part of the engineering process. How the "exposure factor" works is as
follows: the engineering data provides maximum allowances for a particular
material at a given wind speed. The "exposure factor" simply multiplies those
allowances. See the following paragraph below for an example.
An example would be: If you have 120 M.P.H. wind loads in
your area, then you might be able to have a post height of 8' 0" for a
particular post based on your structure's design. With exposure "B", the
multiple is 100% and therefore there are no changes to the allowed post height.
But if you are exposure "C", then the multiplier might be 91%. Thus the new
maximum height allowed for a particular post might only be 7' 3". If that post
height wasn't tall enough for your project, we would have to change to a
stronger post.
(You should be aware that there is not just ONE
multiplier which applies to a particular "exposure factor". There are a series
of numbers which have to be applied based on different conditions. But you don't
need to worry about that because that is all a part of the engineering process.
You only need to provide us with the "exposure factor" so we can do the rest.)
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How many "exposure factors" are there anyway, and what do
they mean?
There are 4 exposure factors.
Actual definitions are quite
comprehensive. However, the "exposure
factors" can be summed up as follows:
"A" - downtown urban areas surrounded by high rise structures (not covered by
our engineering)
"B" - typical residential areas surrounded by houses - the vast majority are
this category
"C" - on a lake or other large open flat terrain
"D" - on the coast
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Once you have all this information, how exactly is it
used?
Based on all this information we can then design a
structure. All aspects of the structure and sizes of components are affected. By
using the engineering, we can design the most affordable materials package which
will still meet all requirements. Which is the point of engineering - to design
a strong structure as economically as possible.
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With all of the hurricanes in recent years, should I go
beyond what the engineering requires and build a stronger structure?
That is a personal decision, but in general we would say
no. Before deciding, you may want to consider the following:
- In 2001 there was a major change made to the
Florida building
code affecting all of the structures we sell. The hurricanes of 2004 proved in
real world situations that those code changes actually work; structures built
after the code changes were far more likely to survive.
- In 2007 there was a change to the engineering
requirements which once again made structures stronger.
- Many older structures built long before codes were
strengthened are still standing.
- "Failure" to
an engineer or the building code
does not mean exactly what you may
think. You might think it means the
structure collapsing, but "failure"
really has to do with how much
materials are allowed to bend or
deflect before they are considered
to have "failed". Excessive bending
or deflection can certainly cause a
structure to collapse, but the
actual amount of bending or
deflection allowed by code is not
based on structural collapse, rather
consensus of experts.
- Regardless
of how well designed, ALL structures
have a weak point. Unfortunately
there is no way to know exactly what
that weak point is. You could easily
miss the structure's weak point when
upgrading materials.
- All
engineers build a factor of safety
into their designs. These structures
will not simply collapse just
because winds were 1 or 2 M.P.H.
higher than the design allowed.
- Because of
the unpredictable nature of winds
during storms, your property could
see winds much higher or lower than
winds recorded only a short distance
away. When it comes to upgrading,
how much is enough?
- Unless you are building a free standing structure, your
new structure will attach to your house. No matter how well engineered your new
structure is, it is only as strong as what it is attached to. If the winds are
high enough to damage your house, your new structure may not survive anyway no
matter how strong it is.
- According to failure analysis done by engineers to failed
structures after the hurricanes, the largest reason for failure was NOT the size
of the materials used, but rather the way those materials were fastened. Too
often fasteners had corroded due to neglect, were too small, too few were used,
or they were improperly installed. By the way, these were typically contractor
built structures which were investigated, not homeowner built structures.
- Think about the use of your new structure. Will you use
it as shelter during the storm?
- Provided you build your new structure to the engineering
requirements and have followed the appropriate permitting requirements, the
structure will in all likelihood be covered by your insurance policy.
- However, there is one reason why
we might want you to
consider building a stronger structure: it increases our sales revenue!
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Is this engineering design all I need to get my building
permit?
We recommend you read our section on building permits
here. In general, along with other requirements of the building permit, you will
need 2 sets of signed and sealed engineering drawings in order to be able to
pull a building permit. Check with us about signed and sealed engineering
drawings. Please note that the price of the material package does NOT include the
engineering.
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What is the difference between generic engineering and
site specific engineering? Which do I need?
Generic engineering shows a typical project type (for
instance a screen room) along with all of the materials which could be used to
build the project and the materials' limits. The generic engineering does not
contain a drawing of exactly what you will be building. Usually generic
engineering is acceptable because it includes an engineering analysis of all
the products you will be using to build your project and it has been signed and
sealed by a certified engineer as required. Best of all, generic engineering is
usually substantially less expensive than site specific engineering.
Site specific engineering is exactly what it sounds like.
You will hire an engineer who will design your project for you and include
drawings specific to your project. In some situations you may have to use site
specific engineering, but generally you do not. (Call us for more info on this.)
If you have site specific engineering done, your project design will very likely
change from what we have provided for you. Therefore we will have to adjust your
materials package accordingly. (You must build exactly what is shown in the
engineering or else it will be rejected by the building inspector.) By the way,
if you will be hiring an engineer to produce site specific engineering, we
recommend hiring an engineer familiar with the industry standard materials. Too
many times engineers who are not familiar with the materials readily available
have specified building materials from industrial sources. Those materials may
be very difficult to find locally and are very expensive. There are engineers
who specialize in aluminum design.
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When should I get the engineering and apply for a permit?
We recommend
obtaining the engineering after we have
completed the design to your satisfaction, but BEFORE you buy any materials from
us. Experience has taught us that getting a building permit before ordering
materials is the best way to go.
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Why don't they just have
specifications we can follow which will be acceptable?
The state of Florida and the Aluminum Association of
Florida are working on exactly that. And they have been for at least a decade.
At some point in the future you will be able to build a project as long as you
follow specific guidelines. And that will eliminate the need for signed and
sealed engineering documentation. However, you will still have to "engineer" the
project to ensure it meets the guidelines and present paperwork to the building
department showing that it does.
An early form of this system in fact already exists,
however it uses the engineering requirements from Miami-Dade (the most stringent
in the state). Most building departments, however, do not accept it yet, and
structures designed to those standards are considerably more expensive than
using our engineering. Until they work out the kinks in the system, you
are much better off using our engineering.
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*Please note: This information pertains
primarily to the materials packages we sell such as screen rooms, car ports,
etc., and not to the products we sell such as awnings, windows, and others. We
have made every effort to provide you with accurate and up to date information,
however we make no guarantees as to the accuracy of the information provided.
You may want to verify the information we provide here with your local building
department and/or a licensed professional engineer.
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