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Plan & Design |
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Parts Of A Deck
Before diving into Building Codes, obtaining a
building permit, plat maps, easements, and so on, it makes sense to take a
minute to define the basic parts of a deck. In so doing, you can brush up on
your deck building vocabulary and also get a brief exposure to some of the
considerations related to deck framing.
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Ledger Board: Whenever the deck is
attached to the house, a ledger board is used. In general, ledger boards are
the same size as the floor joists. After selecting a straight piece of
lumber for the ledger board, the ledger is bolted to the house's
framing. Given the potential for injury should the deck break apart from the
house, it's important to select the right
type of bolt, as well as, the correct size and spacing of bolts to handle
expected design loads. Similarly, to avoid water damage to your home's
framing, it's important to install sheet-metal flashing that prevents
rainwater from getting between the ledger and the home's framing.
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Point - Most treated lumber sold is wringing wet - with a
moisture content of around 65%. What most people don't know is that lumber
with a moisture content above 19% does not hold nails as well, has weaker
bolted connections, and isn't as strong or stiff against bending as dry
lumber. When you
build your deck or gazebo, make sure you understand how to compensate for
"wet service" conditions. For a very modest price you can get
a password and have instant access to all
the wet lumber design information you'll need to make sure your deck and/or
gazebo won't fail under heavy loading.
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Floor Joists: In general, "2x"
(two-by) lumber with an actual thickness of 1-1/2" is used for floor
joists. Probably the most common floor joist size is 2x8 lumber - actual
size is 1-1/2"x7-1/4". The species of lumber, the spacing of the
joists, and expected design loads all determine what size floor joist is
required.
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Place Crown Up On All Joists
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Tip: Most boards have a slight "crown" to them. To check for
crowning, hold one end of the board about a foot from your nose with the
other end resting on the ground. With the wide side up, sight down an edge
of the board. If there is any crown, your eye will easily see the edge
as being slightly curved. When you install your joists, place all the joists
with the crown up. In so doing, you'll get a more consistent floor surface.
Later on, when you install the decking and furniture, the extra weight will
work to flatten out the crowns resulting in not only a consistent but also flat
floor surface.
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Solid Blocking: Blocking keeps taller
joists from twisting onto their sides when heavily loaded. In
general, blocking is just short boards cut from the same size lumber as the
floor joists. In fact, you should set the most warped joists off to the side
and cut them up for blocking.
By 2003 International Building Code (IBC), blocking is required every 8 feet
for 2x10 and taller joists. In other words, the distance between any two
rows of blocking, or any one row of blocking and the end of the deck, can
not be more than 8 feet. It should be noted that the blocking doesn't
necessarily have to be centered over the length of the joists.
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Support Beam: The beams take all
the weight from the floor joists and transfer this load onto the posts and
ultimately to the concrete footings in the ground. Although there are special
composite lumber exterior grade beams, usually either a solid
lumber beam or a built-up beam is used.
A solid lumber beam is just that. It's a single thick and wide piece
of wood. For example, a 4x10 solid beam is 3-1/2" thick by 9-1/4"
tall. Built-up beams are made from nailing together two or more
"2x" boards. In practice, the use of one type of beam over the
other is solely a function of what part of the country you live in. Both
types of beams are perfectly acceptable.
Check
Point - Metal joist hangers are used to attach the floor joists to the
side of the ledger board. The capacity of joist hangers depends on many
factors such as the joist hanger design, the diameter and length of
the nails, the nailing pattern, and whether the ledger board was "wet"
at the time of installation. Be careful not to exceed the
capacity of your hangers. Make sure you understand how to adjust the
rated capacity of your hangers for the application and also know how
to determine the load the joist hangers must carry. For a
very modest price, get a password and have access to easy-to-read hanger tables and expert advice that'll ensure your
deck hangers are strong enough.
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Band/Rim Joist: Band joists, also
sometimes called rim joists, are just joists at either the side or end of
the deck. There's nothing special about them. In fact, unless you've got
stairs attached to one of them, band/rim joists only have to carry a
fraction of the load that the regular floor joists do.
Tip: In the deck above, the ends of the floor joists and beam are
cantilevered. This means that instead of ends resting directly on a support
part of the framing, they project out past their supporting member into thin
air. When cantilevers are used, it's easier to frame a deck since the
posts and beams don't have to be perfectly aligned. That is to say, if the
posts aren't spaced perfectly but are at least in a straight line, it won't
matter since the ends of the beam are cantilevered. Likewise, if the beam is
set a bit crooked but the joists are cantilevered, it doesn't matter. When
framing, let the ends of the joists run long during assembly and then snap a straight
cut line after all the joists are in place. If the beam is a bit crooked
underneath, no one will ever know.
The content under the "How-To" menu is a small sampling of all the material covered on BestDeckSite.
For immediate access to in-depth information on easements/set-backs, evaluating the building site,
creating a rough draft of your project, as well as, comprehensive
coverage of all aspects of gazebo and deck building, get a
password and log-in now.
Plan & Design
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