greetings, i am building a deck that will be 17 feet wide by 9 foot
deep. i will use 4x4's dug three feet into the ground, with a bag a
cement in each hole. my question is how much support(4x4)will i need for
the 17 foot span? obviously one 4x4 on each end but will one 4x4
centered be enough or should i break the 17 into thirds? so 4 columns
instead of three?
cj

On Apr 19, 8:07*am, cj wrote:
greetings, i am building a deck that will be 17 feet wide by 9 foot
deep. i will use 4x4's dug three feet into the ground, with a bag a
cement in each hole. my question is how much support(4x4)will i need for
the 17 foot span? obviously one 4x4 on each end but will one 4x4
centered be enough or should i break the 17 into thirds? so 4 columns
instead of three?
cj

it depends on how big your rim joists or outside girders are. or if
you double them. I'm working on a deck now, that is 22' by 14' and we
used treated 2" x 8", doubled. then the rim joists are through
bolted(galvanized 10" bolts), and just for kicks we installed support
blocks under the joists on the posts. On the 22' side, there are 4
posts (including the corner). All joists in between are attached with
hangars and approved nails. Don't use deck screws to attach the
joists to the posts and expect that to be good enough. No shear
strength.
hth
perry

On Apr 19, 8:07*am, cj wrote:
greetings, i am building a deck that will be 17 feet wide by 9 foot
deep. i will use 4x4's dug three feet into the ground, with a bag a
cement in each hole. my question is how much support(4x4)will i need for
the 17 foot span? obviously one 4x4 on each end but will one 4x4
centered be enough or should i break the 17 into thirds? so 4 columns
instead of three?
cj

Better is not to have 4x4 posts below ground as they will rot quicker
but have them attached by metal bracket with concrete above ground by
1" or so.

cj wrote:
greetings, i am building a deck that will be 17 feet wide by 9 foot
deep. i will use 4x4's dug three feet into the ground, with a bag a
cement in each hole. my question is how much support(4x4)will i need for
the 17 foot span? obviously one 4x4 on each end but will one 4x4
centered be enough or should i break the 17 into thirds? so 4 columns
instead of three?

Other posted discussed spacing -- there are online sites that allow you
to estimate deflection based on joist size and support spacing. google
for "sagulator" or a post had the url a day or two ago.

How high off the ground? I'm partial to larger than 4x4 supports unless
it's very low for the extra lateral stability plus they give it a more
solid appearance...

--

cj wrote:
greetings, i am building a deck that will be 17 feet wide by 9 foot
deep. i will use 4x4's dug three feet into the ground, with a bag a
cement in each hole. my question is how much support(4x4)will i need
for the 17 foot span? obviously one 4x4 on each end but will one 4x4
centered be enough or should i break the 17 into thirds? so 4 columns
instead of three?

Don't put the 4x4s in the ground. Consider sonotubes or equivalent with
rebar. Have the concrete foundation above grade by 3-6" and bolt the posts
to that.

"cj" wrote in message
news
greetings, i am building a deck that will be 17 feet wide by 9 foot deep.
i will use 4x4's dug three feet into the ground, with a bag a cement in
each hole. my question is how much support(4x4)will i need for the 17 foot
span? obviously one 4x4 on each end but will one 4x4 centered be enough or
should i break the 17 into thirds? so 4 columns instead of three?
cj


First, refine your building technique and design. Burying a 4 x 4, even
pressure treated is not a good idea. Pour the concrete in a Sonotube and
get them level. Use the metal brackets designed for the purpose of holding
the wood in place above the water that will rot them.

You need at least 4 posts on the 17' dimension and one in the center of the
9' dimension.

Other considerations:
Lumber comes in 8', 12', 16' lengths so 17" is going to be a PITA. 16' is a
breeze by comparison.
That 9' width is going to need a 12' support. You may find 10' and only
waste a foot of wood. If you cut down the 12' joists use the cut offs for
cross bracing.

Use the proper screws and brackets. check out www.mcfeelys.com for a lot of
good deck and fastener information.

On Apr 19, 8:07*am, cj wrote:
greetings, i am building a deck that will be 17 feet wide by 9 foot
deep. i will use 4x4's dug three feet into the ground, with a bag a
cement in each hole. my question is how much support(4x4)will i need for
the 17 foot span? obviously one 4x4 on each end but will one 4x4
centered be enough or should i break the 17 into thirds? so 4 columns
instead of three?
cj

You've got your whole project bassackwards. Take a breath here and do
some logical planning.

1) You will have to have a building permit in most communities.
2) A permit requires a set of plans with specifications such as
dimensions and materials.
3) The plans must meet the city building codes.
4) Many box stores have free deck planning services. Take advantage of
it.
5) Once you have applied for and received your permit, all your
questions will probably have been answered.
6) If you need clarification of any details, the inspectors in the
office can be amazingly helpful...all you have to do is to ask and
then listen.

Common sense says that reinventing the wheel is the curse of the
ignorant. Find out where the knowledge and expertise is in your area
and go for it. Good luck.

Joe


Unless you have a degree in civil engineering and lots of construction
experience it makes no sense at all to wade into any large project. .

On Apr 20, 3:02 am, Joe wrote:
On Apr 19, 8:07 am, cj wrote:

greetings, i am building a deck that will be 17 feet wide by 9 foot
deep. i will use 4x4's dug three feet into the ground, with a bag a
cement in each hole. my question is how much support(4x4)will i need for
the 17 foot span? obviously one 4x4 on each end but will one 4x4
centered be enough or should i break the 17 into thirds? so 4 columns
instead of three?
cj

You've got your whole project bassackwards. Take a breath here and do
some logical planning.

1) You will have to have a building permit in most communities.
2) A permit requires a set of plans with specifications such as
dimensions and materials.
3) The plans must meet the city building codes.
4) Many box stores have free deck planning services. Take advantage of
it.
5) Once you have applied for and received your permit, all your
questions will probably have been answered.
6) If you need clarification of any details, the inspectors in the
office can be amazingly helpful...all you have to do is to ask and
then listen.

Common sense says that reinventing the wheel is the curse of the
ignorant. Find out where the knowledge and expertise is in your area
and go for it. Good luck.

Joe

Unless you have a degree in civil engineering and lots of construction
experience it makes no sense at all to wade into any large project. .

Time and time again, every time I poke my nose into one of these
forums I see posts that are the equivalent of asking "how long is a
piece of string". often the poster has made up his mind before he asks
a question.

To the OP and just about everybody else who cares to listen, the post
by Joe should be read, read again and probably copied so that you
don't forget.
After 50 years in the game I could not have put it better. He is spot
on.
Just in case you want to check me out look at my brief page on decks.
http://www.builderbill-diy-help.com/deck.html

To reinforce what Joe has said, I am this afternoon going to look at a
house with a structural engineer and a real estate person. The place
has had illegal additions to it, the owner wants to bring these up to
the current standard. The reason for this? The owner wants to sell
but has only had offers up to $320,000. Similar houses in her street
have sold for over $400,000.

It would have cost her a fraction of the cost she is faced with now,
to do it right in the first place.

Cheers
Bill.