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Old 09-26-2011, 10:04 AM   #1
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Freestanding 16 x 14 deck questions


Quick question.

I'm building a freestanding 16 x 14 deck near the house. House outline and other items won't allow an attached deck without severely comprising usable deck space (width).

Anyway here's the specs of my plan:

Deck floor height from ground will be 36".

Footings for deck posts will be concrete (local code: footer is dug 12"x12" and 18" deep, min concrete is 8" I'll probably go deeper)

I'll be using (9) 6x6 posts.

Beams will be 2x8x16 (doubled) cut to 14' length, jointed to posts with post caps (nailed).

There will be a 12" overhang all the way around. In other words the rim joist outer edge will be 14.75 from the center of the outer posts.

Joists will be 2x8x16 using joist hangars, corner brackets and hurricane ties where they meet the beams.

I'll be using blocking as well.

Beam spacing will be 6' 9.25" (post center to post center)

Each beam will be made up of (3) 6x6 posts spaced at 5' 9.25" (post center to post center)

With this configuration is it overkill to put the joists at 16" on center? Would 24" on center work?

Trying to make the least waste of lumber, but also not looking to build JUST to code, but a SOLID deck that will last.

Thanks!


Last edited by ctandc; 09-26-2011 at 10:06 AM.
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Old 09-26-2011, 10:40 AM   #2
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Freestanding 16 x 14 deck questions


Does code call for 9 posts? My free standing deck is 16 x 14 and only has 6 posts.

My joists are 16" on center FWIW - I don't think i could have gone 24. The inspector told me 12" on center if the decking runs at a 45 degree angle and 16" is OK if you have them perpendicular. I think I rememeber him saying that if you use composite it has to be 12" OC no matter what direction it runs in, but don't quote me on that.

At that height you'll need a railing.

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Old 09-26-2011, 11:19 AM   #3
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Freestanding 16 x 14 deck questions


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Originally Posted by CoconutPete View Post
Does code call for 9 posts? My free standing deck is 16 x 14 and only has 6 posts.

My joists are 16" on center FWIW - I don't think i could have gone 24. The inspector told me 12" on center if the decking runs at a 45 degree angle and 16" is OK if you have them perpendicular. I think I rememeber him saying that if you use composite it has to be 12" OC no matter what direction it runs in, but don't quote me on that.

At that height you'll need a railing.
What kind of overhang do you have with 6 posts?

What's the spacing between posts?
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Old 09-26-2011, 11:40 AM   #4
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Freestanding 16 x 14 deck questions


With 2X8 floor joists that long you will have some serious bounce. If it were mine I would go with a center beam to remove as much bounce as possible. My floor joist would never go over 16 inch center line. I also would brace brace brace on a free stand.
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Old 09-26-2011, 12:29 PM   #5
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Freestanding 16 x 14 deck questions


You did not indicate where you are building, or which code you are working under. If you are working under the International Residential Code (IRC), you should obtain a copy of the Prescriptive Residential Wood Deck Construction Guide (my building inspector gave me a copy when I pulled my permit). If you check table 2, it shows maximum allowable joist spans for various lumber species. For southern pine, maximum span at 16 inch oc is 10'6" for a 2x8. If I understand your post correctly, you are planning 16 foot span for the joists, which would be well beyond allowable span. The guide is very good, has useful diagrams, and is clearly written. I recommend it even if you are not subject to IRC.
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Old 09-26-2011, 02:31 PM   #6
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Freestanding 16 x 14 deck questions


Maybe I'm missing something.

I thought Joist Span was measured by the load bearing center, not counting over hang?

I've attached a rough diagram, I've actually got the deck designed in Google Sketch Up as well.



(Excuse the drawing, I just did it to post what I'm talking about. And the lengths between posts should be 5ft 9.25" and 6ft 9.25" (not 9/25)

Overhang is only 14.75" from the center of the 6 x 6 post. I would be adding bracing to every pair of joist runs as I install them.

According to the DCA (Prescriptive Residential Wood Deck Guide)

Southern Pine 2 x 8 joist with an overhang, at 24" OC is 10'-2". My joist spans (center of post to center of post) is only 6ft 9.25" span.

Am I missing something? I thought my deck design would be overbuilt if anything

Last edited by ctandc; 09-26-2011 at 02:37 PM.
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Old 09-26-2011, 03:11 PM   #7
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Freestanding 16 x 14 deck questions


I misunderstood your post, the diagram cleared it up. You are correct, joist span is measured as the c-c distance between supports, so you are OK. Probably is overbuilt, but that is rarely a problem.
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Old 09-26-2011, 04:36 PM   #8
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Freestanding 16 x 14 deck questions


I misunderstood also, looks like you got it covered. I still would shoot for 16 inch centers.
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Old 09-26-2011, 04:45 PM   #9
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Freestanding 16 x 14 deck questions


IMO that’s not overbuilt, just well built.

What are you planning for the decking?
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Old 09-26-2011, 10:01 PM   #10
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Quote:
Originally Posted by kwikfishron View Post
IMO thatís not overbuilt, just well built.

What are you planning for the decking?
5/4 x 6 x 14

The local lumber yard has some stuff treated under the "eco life" brand.

$8 a board. $4 cheaper than the local box store.
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Old 09-27-2011, 11:51 AM   #11
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Freestanding 16 x 14 deck questions


Defiantly go 16” OC for 5/4 decking.
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Old 09-27-2011, 12:46 PM   #12
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Freestanding 16 x 14 deck questions


Here's a screenshot of the deck in Google Sketchup. I changed to 16" with the joists.


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