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I am planning to build a ground level deck in bay area in northern California where we have pretty nice weather, and no snow in my living area. I am looking for feedback with following specs

  1. finish height 13"
  2. on existing uneven concrete patio (highest to lowest is around 1.5")
  3. composite deck 1" thickness
  4. 16" OC for internal joist
  5. most of the time it should be empty deck and no huge furnitures.

I used decks.designer.com to draw a fairly simple layout.

enter image description here

Questions

  1. is 2x8x10 PT Hem fir ok to span a little less than 10' for internal joists? I looked on decks.com and for 16" O.C, it claims 11'-1" for span.
  2. Rim beams: I am planning to use double 2x8x8 for the rim beam for long sides only (22'), which should give me around around 7' span for double 2x8. Or I need more footing to support shorter span?
  3. Is 4x4 posts enough? Or I need to use 6x6 posts? I know 6x6 will meet all codes, but wonder if I can just use 4x4.
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    are you going to slope it away from any structures? I like storage so I typically 2% slope it, plywood the deck, torch on membrane, add sleepers for level, composite to finish. nice dry storage underneath. deck framing never gets wet should last 100 years. Most code says wood at least 6" off ground - are you doing concrete pillers to sit the posts? Mar 18, 2021 at 7:06
  • You write "on existing uneven concrete patio" - do you intend for your new deck to have free space between the joists and the existing concrete or would they be resting on and supported by the existing concrete?
    – brhans
    Mar 18, 2021 at 10:21
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    I note that you say you're using 2x8x8 for your rim joists, but your drawing doesn't show that - it shows one @ 2x ~14' and one @ 2x ~8'. Just checking that your words are off instead of the drawing being off. The way it's drawn seems like a much better idea than the way you have it worded.
    – FreeMan
    Mar 18, 2021 at 14:19
  • @brhans i would have free space between joists and existing concrete.
    – bj4947
    Mar 18, 2021 at 16:20
  • @FreeMan the drawing is off, I see that using 14' is good but i will be a bit hard for me to find such long lumber. my easy accessible lumber is 8' long and I am planning to joint them on the points which should break them into three ~7' sections. does it make sense to you? thanks for the feedback!
    – bj4947
    Mar 18, 2021 at 16:22

3 Answers 3

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Have you considered a floating deck - a.k.a. "Dek Blocks"? That makes a totally DIY project, and depending on location, either no permits or minimal permits. No concrete to pour, no digging. Deck sits on special blocks instead of being anchored to footings. Deck is not attached to house. There are height limitations, but 13" is effectively "nothing" (or ground-level as you stated).

I have no affiliation with the manufacturer - just built one myself (with my evil twin helping) several years ago, 14' x 14'.

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  • yeah, i thought about it. but I am still facing the same issues for the spans and rim beams...etc., right?
    – bj4947
    Mar 18, 2021 at 6:03
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    There is a difference because instead of depending on a few widely spaced footings, you can use a bunch of more closely spaced blocks. Mar 18, 2021 at 6:12
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You don't mention anything about the foundation. Unfortunately that's likely to be the most painful part of this project.

When you put a deck like this on top of a patio you are essentially putting all the weight that was evenly spread out over the patio on the 8 points supporting your posts. Unless the patio is very thick there is a danger that you could crack the patio.

The right way to do this would be to either remove or cut holes in the patio. Dig holes to the required depth and width and build the appropriate foundation (30" deep and I think 18" wide). If you don't do this you will likely have problems.

I haven't used them but the deck blocks could be better as you would likely have a lot more point loads. This would also minimize your worries about spans etc.

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  • I have concrete patio now (as pointed out in OP) but I forgot mention is thickness, i think it should be 4-5" thick concrete slab.
    – bj4947
    Mar 29, 2021 at 16:32
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Sir. Save your money and go single band use what you save on extra band and use extra 4x4s upright 4 foot O/C simply use one screw in the middle of band board to hold in place while drilling your carriage bolt holes you can also once your band boards are all on have some PT 2x4 and cut to place under your band boards to the concrete and simply screw them in and I agree with the gentleman that mentioned 12 inches " O/C on your joist I would also simply use galvanized carriage bolts on your band board. Some composite decking has more sponge than others reason better to go 12inches O/C on joist, free float the hole deck,deck blocks are not necessary in truth It is my advice best not to attach to house If you want really solid I would put 4 4x4s down the whole 22 foot run in center of 10 foot at the 5 foot mark with a under the joist 2x6 attached with carriage bolts as well or screws. No higher than your going to be off the ground and as long you have 3.5 inch concrete slab You will love the strength and no movement. I'm sure you will enjoy the project just my two cents from the Woolywagon guy

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