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Old 06-08-2007, 02:04 PM   #1
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Deck beams


Do you pros always use double 2x's for beams/ joist bans? I'm using 2x8 pt lumber for a 12x16 deck. 5/4 deck boards.

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Old 06-08-2007, 02:42 PM   #2
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Deck beams


Since this is a freestanding deck, I will use doubled 2x8's all around, I guess.

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Old 06-08-2007, 04:19 PM   #3
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Deck beams


Quote:
Originally Posted by boman47k View Post
Since this is a freestanding deck, I will use doubled 2x8's all around, I guess.
Boman,

I must say that decks should never be built by 'guessing'.

Decks should always be built by calculations.
Your preliminary design will dictate your calculations. Your calculations will give you your dimensions for your beam, footings, joists and other key structural information.
These all contribute to the overall structural stability that equal, your safety and the safety of all those that you care about.

There are mathmatical/engineering reasons for specific lumber dimensions, footing sizes/depths, post-placement distances, beam depth and width, why certain joists are doubled, why a beam is tripled, and so forth. Code requirements for connection points and what fasteners to use.

Example of other factors - Do you know what a ''crown'' is on a stuctural piece of lumber that will be used for a joist? Do you know where that crown should face? This is very important.

Check with your local area to see what requirements or guidelines your building dept. has for constructing a deck.
Please do alot of research concerning general deck structural design and weight load calculations. Once you do that, do your design on paper before you attempt anything. Have someone with experience look it over and critic it.... Please ?

Review joist span information and structural requirements. In most US jurisdictions, a building permit is in fact, required to build a deck. For starters, Use 2x10's (not 2x8's for that span).....

Here's some examples of Town/City requirements for decks (please check YOUR local requirements):

http://www.richmond.ky.us/Department...on%20Guide.pdf

http://www.volz.org/dkspecs.htm

http://nashua.qscend.com/filestorage/51/70/151/Deck.pdf

Last edited by AtlanticWBConst.; 06-08-2007 at 07:02 PM.
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Old 06-09-2007, 07:44 AM   #4
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Deck beams


Thanks for the response, Atlantic. Yes, I know what the crown is and know which way to point it. I am going slow on this thing so I can gather info and understand as much as I can before I proceed. From what I have read, doubled 2x8's should be okay with posts no more than 8' apart with a doubled 2x8 in the middle. Which brings me to another question. Which way should the middle beam go on this deck across the 12' or the 16'? I have not read the links you posted yet, but I intend to. This deck is only about 30" at its highest point. I have seen some decks around here about 12' to 15' high with 4x4 posts. I have to wonder about them everytime I pass them. Heheh, not sure I would want to get on them.
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Old 06-09-2007, 09:35 AM   #5
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Quote:
Originally Posted by boman47k View Post
Thanks for the response, Atlantic. Yes, I know what the crown is and know which way to point it. I am going slow on this thing so I can gather info and understand as much as I can before I proceed. From what I have read, doubled 2x8's should be okay with posts no more than 8' apart with a doubled 2x8 in the middle. Which brings me to another question. Which way should the middle beam go on this deck across the 12' or the 16'? I have not read the links you posted yet, but I intend to. This deck is only about 30" at its highest point. I have seen some decks around here about 12' to 15' high with 4x4 posts. I have to wonder about them everytime I pass them. Heheh, not sure I would want to get on them.
If you are planning the foot print of the deck ot be 12'x16':

You should use 2x10's for your joists because of the span being over 10'. Your rim joists are always going to be doubled and overlapping. You inside joists will be singles. Your main carrying beam should be what the town/code dictates. We prefer tripled 2x12''s on 6x6 posts.

I assume that the 16' will be attached to the house, with the deck extending out 12'. You should run your main carrying beam cantilevered inward approximately 2' from your rim joist in the manner below to support the entire run of 2x10's and the outside of the deck itself:


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Old 06-09-2007, 11:03 AM   #6
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Deck beams


Actually, I was planning on a freestanding deck with the 16' running perpendicular to the house. I may be misunderstanding the term 'span'. I take it to mean from one supported point to another supported point ( on top of post ). My posts are 8' apart on the 16' run and 6' apart on the 12' run. I feel the main beam going down the middle needs to be run perpedicular to the house the same as the 16' run. I did not drop back for the cantilever. I can see the point to that though. I think I may just pay a visit to the building dept before I proceed. I may try to get a footprint on here a little later.

Sidenote : I was telling my wife this morning that if people knew what all went into any given project to get it right and safe ( in this case ) they would have a better understanding of the prices that are charged. Heheh, 'right' includes safe.
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Old 06-10-2007, 08:41 AM   #7
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Deck beams


Boman,

Sorry about the misunderstanding regarding your deck design. However, the points I wrote about structural support and the site links are still relavent.

Here are two more links to help you out:

1.) Basics (you may be all set with this info already):

http://www.startremodeling.com/builda.htm


2.) Example of a free-standing deck design (look at page #6 & diagram # 8):

http://www.ci.lancaster.oh.us/dept/c...%20%201105.pdf

Last edited by AtlanticWBConst.; 06-10-2007 at 01:14 PM.
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Old 06-11-2007, 12:03 PM   #8
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Deck beams


Talked to the guy at the Building Dept. today. Seems to think I'm okay with the doubled 2x8's with sway bracing at my posts. Told me to plug away. Nothing about a permit or anything. Little wonder there are some funny looking decks around here. I did look at a site someone had posted to look for deck permits in this city. Could find no reference for decks. After doing some reading on the sites you posted, Atlantic, I wonder if I even need the beam in the middle of the deck if I ran the beams parallel to the house. It so happens I am running them perpendicular though (3 beams, 16' long). This puts my joist at about 6', and I may go with 2x6's for them for the 12' part. Didn't think to ask him about whether pt was required for the joists. If pt is not protected from water and up off the ground, I'm not sure I can see the advantage of it. My house has places lower than the lowest part of this deck with no pt joists. I think I am correct on that. It is an old house though.

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