EXTERIOR WOOD DECKS
Contents
of this page are the Copyright of and reproduced with the
permission
of:
Criterium
Yingst Engineers
421 W. Chocolate Ave., Hershey, PA 17033
1-800-231-3346
EXTERIOR WOOD DECKS: This time of year, exterior wood decks
become an integral part of our homes. Unfortunately, these same
decks are subject to severe weathering over the years often
leading to deterioration. Every year, people are injured or
killed when a deck fails. Thus, it is important that all decks
be properly built and maintained.
When
listing a home, take a good look at the deck. Does it stand
straight "Ready for duty, SIR!" or slouch and lean, leaving you
with the sense that it would rather not be used? Is the deck
ready for parties and significant structural loading? Are the
railings weak? Does the floor sag? Has it been properly
maintained? Just how safe is the deck?
All
new decks (built since July, 2004) should meet the
requirements of the International Building Code (IBC), 2003
Edition, or its companion document for one and two family
dwellings, the International Residential Code (IRC), 2003
Edition. If the home was built during or since 2004, a
final inspection and occupancy permit will provide an indication
if the deck was built to current building code standards.
Beyond this, here are some important guidelines for a safe and
sound deck.
Wall attachment. The 2003 edition of the IBC (section
1604.8.3) states that a deck "shall be positively anchored to
the primary structure and designed for both vertical and lateral
loads." In addition, "such attachment shall not (emphasis
added) be accomplished by the use of toenails or nails subject
to withdrawal." Essentially, when such an attachment is
not possible, the deck should be freestanding. Toenails are
nails driven diagonally to attach framing members perpendicular
to each other. This type of nailing has little structural
capacity.
In other words, your deck should be solidly connected to the
wall that supports it. SOLID is the key word, with bolts, not
nails.
Floor capacity. The capacity of a deck floor, according to
IBC, should be the same as the adjacent floor in the house,
which would be 40 pounds per square foot for most homes.
In other words, the floor of your deck should feel solid. A
200-pound adult should be able to jump up and down on the deck
without causing excessive or alarming vibration or flex.
Railings.
The deck perimeter should have a railing at least 36 inches
high to meet the IRC requirements and preferably 42 inches high.
At this height, if you are leaning against the railing and slip
you will, most likely, fall inside the railing, not over it. If
it is significantly lower, you are more likely to fall over the
railing. Ironically, a railing built to the proper height often
obstructs your view when you are sitting in a chair on the deck
behind the railing. However, ensuring a good view should not be
considered an acceptable reason to compromise safety.
On older decks, and practically speaking, make sure your
railings are at least 36 inches high. Use a tape measure to
confirm that.
A
railing must be strong; it should be solidly anchored and
stable. IBC says a railing must be able to resist a 200-pound
force applied in any direction at any point along the top and
have attachment and supporting structure adequate to transfer
that force into the building (section 1607.7.1).
In other words, a moderately fit adult male should be able to
grab the top rail and soundly push and pull on it without
causing a significant amount of movement or distortion.
A
railing should have intermediate balusters spaced such that
the opening between them does not exceed 4 inches, according
to most codes. This is to prevent children from crawling
through a railing.
Railings should not have integral benches that encourage sitting
on the top rail, with the risk of falling over. Even though
most of us guide our lives with good common sense, when it comes
to sitting on things such as bench railings, we seem to think we
are immune to accidents. The best defense is a good offense;
eliminate the temptation, eliminate the bench rail.
All
stairways with four or more risers should have a railing on at
least one side as required in the IRC (section R311.5.6).
In addition the handrail should meet grip size requirements -
generally a circular cross section with an outside diameter of
1-1/4 to 2-inches or a rectangular section having a perimeter
dimension of 4 to 6-1/4 inches with a maximum cross section
dimension of 2-1/4 inches. Standard 2"x4" or 2"x6" members,
which are often used, do not meet these requirements.
According to most building codes, these standards will apply to
decks at least 30 inches off the ground. However, we recommend
a railing on any deck, even a few inches off the ground, to
minimize tripping hazards.
Joist hangars. Joist hangers should be used at the ends of
all joists unless they are supported by a beam underneath. It
is also important that all of the nails be installed in the
hangers and that proper nails are used. If a ledger board is
used against the house, it should be spaced away from the house
or properly flashed to prevent water entry between it and the
house. The joint between the ledger board and house is a
common area for rot development, and we have inspected many
homes with bad rot in this area - often in as little as three
years.
Deck materials. Older decks (prior to December, 2003) were
generally constructed with pressure-treated lumber using
chromated copper arsenate (CCA). Environmental concerns with
this material led to the voluntary agreement between EPA and the
wood preservative industry to stop producing these materials by
December, 2003. While health concerns with the older CCA
material have been raised, EPA stopped short of calling it
dangerous. In addition, we are not aware of any credible
studies that quantify any actual safety risk with these
materials. EPA has also stated that there is no current reason
to remove or replace CCA-treated structures. For further
information regarding CCA-treated products go to
www.epa.gov.
If you
are constructing or repairing a deck with newer products, you
should be aware that any metal connectors (joist hangers)
should be stainless steel or hot-dipped galvanized fasteners.
Other connectors may be prone to corrosion and ultimate
deterioration. When selecting a deck material and metal
connectors, we recommend that you review the specific
requirements for the products in use. One useful source for
connector information is the Simpson Strong-Tie company at
www.strongtie.com/info.
Decks
are great enhancements to any home. However, they can be
hazardous if not built well and properly maintained. A
periodic, thorough examination of any deck should be performed
as a part of normal home maintenance.
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