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I am planning to build a deck to my backyard, and I'm using a soft wood - I guess it's spruce not sure / not a very high quality wood.

I am having hard time to decide on choosing the construction method and hoping I can get a suggestion here. In short I'm concerned of making a weak frame or having a too tall frame.

I feel like option 3 and 4 are my best bets, it feels strong enough and height-wise it is going to be acceptable for what I'm doing. I just couldn't decide which option to go with.

Let me list all my options my concerns regarding to them:

Note: I am planning to put 9 10cmx10cmx20cm legs under this frame.

Note2: Joist hangers are not an option in where I live, can't get them locally and couldn't find any shipping to Turkey for a reasonable price. (let me know if you know a seller in Turkey :)

Note3: Joists are 5cm X 10cm (2" by 4"), Stringer is 10cm X 10cm (4" by 4").

Note4: Deck size is 390cm X 290cm (12'9" x 9'6").

Option 1:

Option1

Pros

  • Overall height is short enough that I can easily put the frame and the planks on them in my 15cm of skirts.

Cons

  • I'm afraid it will be too weak.

Option 2:

Option4

Pros

  • It will be plenty sturdy.

Cons

  • It is too tall (20cm) and will not be hidden in my 15cm skirt all around the deck.
  • Not sure how I can join 10X10 and 5X10 on top of each other.

Option 3:

Option2

Option 4:

Option3

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  • 1
    What are the lumber dimensions?
    – Chris Cudmore
    Sep 9, 2021 at 17:49
  • For those who are metrically challenged, this deck appears to be about 12'9" x 9'6". Tolga- What are the dimensions of the joists that you're planning on using - that will be most helpful. Also, I suggest you do some research on deck building - you'll find that normally joists sit on top of stringers and that they're not notched into place. If you want to hide the lower parts, either your skirting will be taller, or you put something decorative around the edges to hide the dirty details underneath.
    – FreeMan
    Sep 9, 2021 at 18:32
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    Oops, saw what isherwood was talking about and I concur: 5x10cm and 10x10cm is not sufficient for load bearing on the spans being looked at here.
    – FreeMan
    Sep 9, 2021 at 18:38
  • Tolga, what is that center board doing for you, in your mind? Unless it's a beam capable of carrying all the joists you have laying on it, it really does nothing. If it is intended as a beam it should be substantially larger than the joists it carries.
    – isherwood
    Sep 9, 2021 at 19:54
  • 2x4s spanning for almost 10' felt a little sketchy. Thought it would help to put a stringer/beam (don't know the exact terminology) under them. The legs will be scattered around so that beam is more of a support rather than carrying all joists above.
    – Tolga Evcimen
    Sep 9, 2021 at 20:04

4 Answers 4

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5

Given that you don't have joist hangers, the solution seems clear to me.

  • Set your three posts under three beams.
  • Lay your joists across the beams.
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This way there are no long spans and no concentrated loads. There will also be no butt joints to worry about. Just don't notch anything. You want all the stiffness and strength you can get. Toenail the joists onto the beams and call it good.

You can add a rim joist to the ends if you like, and you could bring the end beams inboard a few inches to create a small cantilever. That might look nicer.

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4

Go to the library and check out a book on building decks. There are commonly accepted specifications and construction methods for decks, and a good book will walk you through the design and building processes.

Also, local building codes may have something to say about the construction of a deck.

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  • +1, and commenting to add that there's good reason for the deck-building standards. Re-inventing this wheel is not a good idea and unlikely to work for long.
    – Fredric Shope
    Sep 9, 2021 at 20:46
  • Thank you. If you have a book name in mind I can look up online. Otherwise, will research myself. Thanks again for the suggestion. Nothing beats good old books for sure.
    – Tolga Evcimen
    Sep 9, 2021 at 21:05
3

How about adding an option (5).

enter image description here

The thinking is to evenly distribute the floor load to the edge beams, so the edge beams will be stressed less and deflect less than a concentrated load from the center joist. Since it is now stiffer and the space between joists is much smaller for the deck board to bridge over, the board can be thinner, and directly nailed to the joists instead of needing other hardware. My answer only provides the concept, as for the size of the lumbers and spacing of the joist, a structural engineer shall be consulted.

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  • The trouble here is that the nine posts are no longer being used. With three posts under each of the beams there would really be no long spans.
    – isherwood
    Sep 9, 2021 at 21:02
  • @isherwood I don't see that's a problem. But OP likes your idea, so it must be it. :)
    – r13
    Sep 9, 2021 at 21:19
1

Lose the middle beam

If the joists need support in the middle use bricks or masonry units or something else that won't rot if it's partially buried.

if you need to prevent the joists from twisting use blocking between them.

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  • 1
    I'm not sure why you'd do this. Now you double the span of the joists, introducing much more bounce. If we were talking about 2x10, sure. We're not.
    – isherwood
    Sep 10, 2021 at 14:11

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