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The Day the Wind Came to Massachusetts:
Well
its finally happened, high winds have come to Massachusetts. Now with
the 7th edition of the Massachusetts State Building Code designers must
resist hurricane force winds. Actually this is not complicated as long
as you understand how winds affect buildings.
When I first came
to Massachusetts from Florida and started my design business I had to
become familiar with the state’s building code. The one item that stood
out to me was no mention of wind loads. No where in the residential
code did I find mention of uplift or shear forces. Being from Florida
we had to deal with these forces for as long as I can remember. I spoke
with some builders and local officials and was basically told, “we
don’t have high winds here.”
Well not being born and raised in
New England I had to do some research to find out about Massachusetts’
history with hurricanes. So I went to web and here’s what I found out (Link):
The
last hurricane to strike was a category 2 hurricane named Bob in 1991.
A category 2 hurricane has wind speeds between 96 and 110 mph. Before
Bob was hurricane Gloria in 1985. Gloria had wind speeds between 75 and
95 mph making her a category 1 hurricane. Before Gloria was hurricane
Belle in 1976, another category 1 hurricane. In 1961 a category 1
hurricane named Esther hit. The year before hurricane Donna, a category
2 hurricane struck. Edna, a category 1 hurricane came ashore in 1954,
and two weeks before that a category 3 hurricane named Carol did a lot
of damage. The Great Atlantic Hurricane that struck in September of
1944 caused severe wind damage all along the southeastern Massachusetts
was a category 3 and the New England Hurricane of 1938 was a category
3. A category 3 hurricane has winds between 111 and 130 mph. I noticed
from this data that we typically have a hurricane every 10 to 15 years,
with the typical hurricane being a category 1 or 2. Hurricane Bob was
17 years ago so it looks like we are on borrowed time.
People
here are the same way people used to be in Florida when it came to
hurricanes, we don’t get them. Believe it or not that’s the way it was
in Florida for a long time.
The first hurricane I remember was
the same Donna (category 4) that hit here in 1960. Next was Betsy
(category 3) in 1965. Our next hurricane was 14 years later named David
(category 5) in 1979. We then went 13 years before we had Andrew
(category 5) in 1992. Its easy to disregard hurricanes when they are
spread out over such a long time. After the past few years people in
Florida take the report of a hurricane seriously.
So its not
“if” a hurricane will hit, its “when”. And if its been a long time
since a hurricane has struck it seems to indicate the next one will
cause serious dama |
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High Wind Provisions of the Building Code:
According
to the 7th edition of the Building Code we must design to resist 110
mph winds, which is upper limit of a category 2 hurricane. And
according to my research that is the typical hurricane that strikes
this region.
When the 7th edition was released in April of 2007
there were five design manuals/methods referenced by the Building Code
for high wind designing in the 110 mph Basic Wind Speed Zones:
1. Wood Frame Construction Manual for one- and two-family dwellings by the American Forest and Paper Association;
2. Southern Building Code Congress International Standard for Hurricane Resistant Residential Construction (SSTD 10-99);
3. Minimum Design Loads for Buildings and Other Structures (ASCE-7) by the American Society of Civil Engineers;
4.
American Iron and Steel Institute (AISI) Standard for Cold-Formed Steel
Framing-Prescriptive Method for One- and Two-Family Dwellings;
5. Concrete construction shall be designed in accordance with the provisions of 780 CMR 51.00 through 99.00.
We
originally had a 180-day transition period before the 7th edition
became mandatory on October 1. Engineers, builders and designers from
Cape Cod questioned the increased wind speed for the Cape as listed in
the new building code. A committee was formed and the formal mandatory
date was again pushed back, this time to January 1, 2008. Because of
the work of the committee an additional method of high wind design was
adopted by the Board of Building Regulations and Standards (BBRS), this
being the “Guide to Wood Construction in High Wind Areas for One- and
Two-family Dwellings by the American Forest and Paper Association.
The
Wood Frame Construction Manual 1995 edition was written after Hurricane Andrew. It
was the first manual to actually address construction with regards to
the physical forces homes must resist during a hurricane. It is full of
tables, charts and diagrams used to perform high wind calculations for
the proper design of homes to resist high wind forces.
After
Hurricane Katrina the American Forest and Paper Association came out
with the “Guide to Wood Construction in High Wind Areas for One- and
Two-family Dwellings”. Basically they took all of the 110-mph wind
information from the Manual and placed it in an easy to follow guide.
In December of 2007 the BBRS adopted this Guide, and created the
Massachusetts Compliance Checklist as a prescriptive method of
complying with the high wind provisions of the building code. According
to the BBRS Official website a home designed according to the Guide and
Compliance Checklist need not be certified by a registered engineer or
architect. By meeting the Guide and Compliance Checklist many of metal
connectors required by the Wood Frame Construction Manual may be
eliminated.
With knowledge of the Guide and the Compliance
Checklist a designer can make simple changes in their designs for
compliance thus reducing the cost of construction. Its not that the
metal connectors are expensive, it’s the labor involved in their
installation that adds up.
How does wind affect your home?
Click on the Picture Below to Find Out.
But I don't wanna change ......
People
never like change. We like to whine when we have to do things
differently, or learn something new. It's human nature to complain. We
like to do today what we did yesterday. But if we do today what we did
yesterday, how can we expect to have more tomorrow than we have today?
A lot of the complains I hear are based upon false information and
assumptions. Lets talk about some of these.
I’ve had people tell
me that all of these requirements are non-sense. They don’t apply to
Massachusetts. It’s the insurance companies out to limit their
liabilities, or window manufacturer’s wanting to make more money, or
the metal connector companies just being greedy.
I’ve had
people tell me that we have older homes that weren’t built by this code
and they’ve survived all of the hurricanes. There are homes that are
built on field stone foundations without any anchor bolts and they’ve
never “blown away”. These statements are all true, but they can also be
misleading. Here’s why:
Look at the actual construction of
these older homes. They were built out of old growth forests, which
means the wood was denser and heavier, interior rooms were smaller
(meaning more interior walls), exterior walls were balloon framed with
continuous studs from foundation to roof, walls were covered with lath
and plaster giving more weight and shear resistance to walls. Today we
built out of light weight woods similar to balsa wood, everyone wants
open floor plans with few interior walls, we build with platform
construction (one floor built on top of another, think of a house of
cards), we use drywall board instead of lath and plaster. We don’t use
the same building techniques or materials that the older homes were
built with. So its difficult to compare the two on equal terms. The
homes today are lighter and weaker than the older homes. So the only
way to build homes of today to be as strong as the older homes is
through proper designing and proper materials, including metal
connectors, or we go back in time and build homes exactly like the
older ones.
I’ve had people tell me you have to use all of
these metal connectors to build under today’s code. It's like building
with an Erector set. This is not true. We do need some metal
connectors, but plywood and nails if used properly can accomplish many
of the connections we need in a structurally sound home. Again it’s
knowledge in materials and their proper usage.
I’ve had people
tell me we have to use hurricane glass in our windows. This is not
true. The building code states that if within one-mile of the mean high
water line of the ocean, and if within a 110-mph wind zone exterior
wall openings must be protected. We can accomplish this by one of three
methods:
1. hurricane resistant glass
2. plywood panels
3. approved shuttering systems
The
people that complain about the insurance companies causing all of this
must remember one point, “they don’t write insurance within the coastal
areas anymore” so they aren't limiting their liabilities with the new
code. Window manufacturer’s would rather produce a “cheaper” window not
a more expressive one, because cheaper sells more. And the metal
connector companies have always made metal connectors that were used in
other parts of the country.
So its not the insurance companies
fault, nor the window manufacturers, nor the metal connector makers.
Its because of the way we build and the materials that we use. Its
because of structural failure of homes in other parts of the country
during storm events. Its from wanting to protect people and their
families during a storm, not having a home collapse on them that have
led to these changes. As Bob Dylan once said, “the times they are a
changin’.”
I must admit it seems there is a lot of confusion
out there on the high wind requirements. This is why designers must
detail the proper construction methods needed to comply with these
building codes. It’s why builders must follow the designers’ drawings.
Recently I had a project that the construction of the required shear
walls was properly detailed for the builder, every nail size called for
and where they needed to go.How to block the panel and the size of
plywood to use. However he failed to follow the detail framing the same
way he had always framed. Needless to say this project “failed”
inspection by the local building official and the builder was required
to “tear apart” his work and redo it to comply with the code.
Unfortunately education costs money, whether in college or the school
of hard knocks.
People never like change. Trust me, I didn’t
like having to change the way I design homes. But we can learn and
adapt to the change, or we can get left behind. Massachusetts is the
last coastal state to adopt the high wind codes. Most of our neighbors
have been doing this the past four or five years. Like all new things
there is a learning curve. In a few years we’ll look back on this an
laugh at the challenges we’re going through now. Notice I said "in a
few years."
What if I have a question?
If you have a particular question regarding the high wind provisions of the Massachusetts State Building Code you may submit your question(s) on our Contact Us page and we'll do our best to answer your question (with our opinion) as soon as possible. Please remember it is the local building official's opinion that counts the most.
If you'd be interested in attending a training course on these requirements please Contact Us and let us know. If there is enough interest we'll be glad to put together a training course.
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Windborne Debris Zones & High Wind Codes, Which is Which?
There seems to be some confusion on the difference in the high wind codes and the Windborne Debris Zone. I've had builders tell me their project doesn't have to meet the high wind codes because it's three miles from the ocean. Some think that the high wind codes only apply if you are located within this "windborne debris zone (see definition below)". Section
5301.1 Design states "Buildings and structures, and all parts thereof,
shall be constructed to safely support all loads, dead loads, live
loads, roof loads, flood loads, snow loads and wind loads as prescribed
by 780 CMR 51.00 through 99.00. The construction of buildings and
structures shall result in a system that provides a complete load path
capable of transferring all loads from their point of origin through
the load-resisting elements to the foundation." The high wind codes applies in the entire State of Massachusetts, with certain areas having a different basic wind speed than others. Table 5301.2(4) provides the basic wind speeds for Towns and Cities in the State. If you're in a 110 mph baisc wind speed zone then your building must be designed according to specific design manuals per Section 5301.2.1.1.
The
7th edition of 780 CMR Massachusetts State Building Code for One- and
Two-Family Dwellings defines a Windborne Debris Zone as areas within
hurricane-prone regions within one mile of the coastal mean high water
line where the basic wind speed is 110 miles per hour. The coastal mean
high water line, in Massachusetts 110 mph wind zones, forms the outer
edge of the red bands overlaid onto the satellite images found on the
MA Department of Public Safety website at www.mass.gov/dps.
In a windborne debris zone as defined above, we must protect openings in exterior wall per section 5301.2.1.2. This is accomplished through use of impact resistant glazing, plywood panels and approved shuttering systems.
So all buildings must be designed to resist imposed wind loads, and those within one-mile of the coastal mean high water line with 110 mph basic wind speed must also protect openings in exterior walls.
Confused yet? Welcome to my world
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This page was last modified on Wednesday, November 11, 2009 04:20:58 PM
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