how to work out joist and bearer spacing and size in decks?


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Old 12-03-07, 03:53 AM
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how to work out joist and bearer spacing and size in decks?

i dont under stand these beam span charts, can anyone tell me how they work??

im gonna build a deck 12 metres long and 4.8 metres wide and i cant work out how far apart the bearers and joists and stumps need to be. Also cant work out what size/length the bearers and joists need to be. anyone help me out here??

deck going to be attached to brick house.
 
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Old 12-03-07, 08:38 AM
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See the example linked below:

http://i240.photobucket.com/albums/f...span_table.gif

You may have to print this to see it clearly, but here's the explanation.

The top section deals with your concern, a deck.

From the left hand column, pick the lumber you plan to use. The top row deals with both the size and spacing of the timber.

The figures where the row and column intersect indicate what is acceptable for a clear span - the distance entirely unsupported from below.
 
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Old 12-03-07, 04:41 PM
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so if i was using #2 doug fir/Larch, 2x8, i can space the joists around 12'7 apart?? whats with the top row, the 12"oc, 16"oc and 24" oc?? thats whats confusing me the most.
 
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Old 12-04-07, 11:23 AM
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The 12" oc, 16" oc, etc. is the spacing of the joists, as in 12 inches 'On Center', 16 inches on center, etc. It is the center-to-center spacing of the joists.

Note that as the OC spacing increases, the allowed spans of the joists decrease. That's because the floor area on top of the joist(s) has a certain design loading, say 40 PSF (pounds per square foot) live load (people and furniture) and 10 PSF dead load (structure weight), and the wider joist spacing thus will apply more floor load to a given joist.

You're always better to go with the deepest joist you can reasonably afford. Deeper joists are stiffer and will result in a more pleasing structure with less noticeable bounce or give to the floor.
 
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Old 12-04-07, 07:51 PM
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TheMechanic,

The span charts are what they are, but the closer together that the joists are, the farther they will span. That's been explained.

The last sentence in your post -- "deck going to be attached to brick house" -- scares me. Are they bricks, or are they blocks??

If they are bricks, make the deck freestanding. BRICKS (i.e. red clay) don't support nothing!!

If they are BLOCKS (8"X8"X16" concrete blocks), then there are anchors that will allow you to properly attah a ledger.
 
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Old 12-05-07, 11:24 AM
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This will make it even easier.

Just fill in the blanks or make the selections that apply to your job, push the button and go!

http://www.awc.org/calculators/span/...e+Span+Options
 
 

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