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Old 05-11-2013, 03:16 PM   #1
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Ground level deck - post placement


New here - first post.

So I've been researching for a while and am pretty clear on the procedure of building a floating deck. What I'm really unclear on is determine the placement and number of deck posts to put down. I know there's a few methods such as triangular calculation and using a grid with stakes and strings. But I'm just not getting how to do this.

Basically I have two questions. What determines the distance between the posts and the position of each post?

My deck is more or less two rectangles perpendicular to one another.

The first is 10ft x 10ft. The other is 14ft x 8ft. The 14 ft side will border the 10ft side of the first square. I can upload a graphic that would probably help but is there an easy method for determine the post placement with this layout.?

I'm sure I'm leaving out a lot of details but I plan to use 2x6s for the cross beams and not sure on the joists. I also plan on using 4x4 rectangular posts. Thanks for any help.

Matt

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Old 05-11-2013, 03:27 PM   #2
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Ground level deck - post placement


Almost never a great idea to build a deck that close to the ground. It needs air flow under it to dry it out. Any reason not to go with a patio instead?

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Old 05-11-2013, 03:29 PM   #3
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Ground level deck - post placement


Here's a pic of my spec. I know it's a amateur sorry.
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Old 05-11-2013, 03:31 PM   #4
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Ground level deck - post placement


@jocaption

I originally wanted to do a patio but the cost is too high for me right now.

Assuming I can raise the deck a bit, can you offer any advice on the post placement.?
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Old 05-11-2013, 03:47 PM   #5
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Ground level deck - post placement


Your posts should be 6x6 or larger. (Forget the 4x4s) Posts are positioned over footings. Footing size and depth is determined by your soil conditions and climate. Distance between footings - and therefore posts - is determined by joist and beam spans. Spans are determined by type and size of lumber, as well as spacing.

Everything you need to know:
http://www.awc.org/publications/dca/dca6/dca6-09.pdf

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Old 05-11-2013, 04:48 PM   #6
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Ground level deck - post placement


Welcome to the Forum!

I'd recommend downloading the American Wood Council's "Prescriptive Residential Wood Deck Construction Guide." This is based upon the 2009 International Residential Code (which may or may not apply to your area). This will give you all of the information you need to know in construction a deck. Give it a read in regards to what you want to do and then post back with any questions.

with that said as joe commented, I've never seen good luck with a deck built on the ground. the closer a wood deck is to the ground the greater the challenge in having proper ventilation under the deck. Stop and think for a moment. the ground has moisture and when blocked by a deck it is difficult for it to evaporate. the bottom of the joists tend to absorb moisture and swell, the tops are dried out by the sun and shrink. this typically causes twisting/cupping of the joists.

you may want to consider (if you're going ahead with the deck idea) of building a free standing deck. less issues with ledger boards and you get more leaway with the construction of the deck. You'll have to verify with your local building department but typically small free standing decks do not require footings that extend down to the frost depth and can rest on ground level piers. Not saying that's how I'd built, but if you are trying to build something inexpensive and you are not concerned about the long term effects (building close to the ground) it's a way to go. again verify with your building department.

it is your deck, we just want you to understand the limitations of a ground level deck.

Good luck!
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Old 05-11-2013, 05:08 PM   #7
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Ok....so reading this document. First question.

Page. 3 Table 2 - Maximum Joist Spans.

Let's take 16" as the space between joists with over hang. This means the span between posts can be 8ft 6in. with an overhang of 2.125ft if I'm using 2x8s? In other words the joist has to hit a beam at least every 8ft 6in.?

Conversely, the beam table on the next page (table 3). If I'm using Cedar 3x8s and the beam size is 18ft, I have a maximum span of 3ft 8in between beems with an overhang of 11in.? In other words, a beam must hit a post of 3ft 8in.?

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Old 05-11-2013, 05:18 PM   #8
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Ground level deck - post placement


no Table 2 gives you the length of your floor joists based upon wood species and spacing, Table 3 provides you with the span between columns/supports for a beam based upon the length of your joists.
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Old 05-11-2013, 05:23 PM   #9
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Quote:
Originally Posted by dephtones View Post
Here's a pic of my spec. I know it's a amateur sorry.
for example in the center of your sketch you have a beam span of 10' if you want to figure out what size cedar beam you'd need to span the 10' you would add together the length of your joists that would attach/be supported by the beam.

10'-6" + 8'-3" = 18'-9". Looking at Table 3 under 18' (even though your deck is longer than this span) joist span you'd see there is no beam configurations that would span 10' if you select cedar as the wood species this means to use cedar you'd have to put an intermediate support at 5', make sense?

wood typically comes in 2' length increments, i.e., 8' 10' 12'. may want to adjust your size so not to have waste. maybe 8' and 10'
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Old 05-11-2013, 05:26 PM   #10
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Thank you. Yes, that makes perfect sense now.
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Old 05-11-2013, 05:31 PM   #11
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be careful of cantilevers ..... read the foot note #2 on Table 2. if you over load (more than 40 psf) on the cantilever you will probably notice the "give" or "bounce" in the deck using these tables. It won't fail, but codes do not concern them selves with perceptional bounce. I typically do not go more than 12" on a cantilever unless I break out my calculator and do some math. I prefer a deck with less give in the joists (personal thing).
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Old 05-11-2013, 05:41 PM   #12
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Ground level deck - post placement


think about furniture and stuff you plan on having on the deck. measure them and draw them to scale along with a scaled drawing of your deck and see how they will fit and how much room you have to get around on the deck. That's how I size decks based upon the needs of the client.

Good luck!
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Old 05-11-2013, 10:10 PM   #13
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I built a ground level deck outside my kitchen back in the fall of 2011. I didn't use footings or posts, but simply supported it on concrete blocks leveled on undisturbed soil. I made sure to leave about an inch of air space below to avoid the moisture issues others have mentioned. I am fortunate in that the area is well drained and so far, I have had no problems. My wife loves being out on the deck and is out there whenever the weather permits. I should have built this deck years ago.
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Old 05-12-2013, 10:14 AM   #14
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Ground level deck - post placement


what about laying plastic under the deck ? have the area graded away from the house, of course. seems to me that this would prevent a lot of problems.
but perhaps there is something i am missing ?

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