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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

Tolga Evcimen
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    What are the lumber dimensions? – Chris Cudmore Sep 09 '21 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 09 '21 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 09 '21 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 09 '21 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 09 '21 at 20:04
  • I would recommend that in addition to searching for deck design info, that you also search for "joist span calculator". This will tell you the minimum size joists you need to span the distances you're looking to span. For example, the American Wood Council has a [span calculator](https://awc.org/codes-standards/calculators-software/spancalc) you can use. (no affiliation, literally the 1st search result). I know that when I went to build my deck, I planned on 2x6 (5x15cm) joists and my building inspector insisted on 2x8 (5x20cm). My joists span about 12', just like your long dimension. – FreeMan Sep 09 '21 at 20:54
  • Thanks for all the suggestions. Although they all sound very reasonable and wise, I have limited options for the wood. The 2x4s and 4x4 is all I have for this frame construction. Guess I'll go with my option 3 as it's the strongest among what I can do. I was hoping for other notched options to be okay, but what I'm seeing here, even option 3 will not be perfect. So, having limited resources, I'll go with a subpar design and will keep the fingers crossed. – Tolga Evcimen Sep 09 '21 at 21:11
  • I would recommend spending some time considering your foundation options. It's a chance to level the deck, and raise it off the ground a bit, if that's of interest. At the low end, you could use a couple of concrete blocks. A poured footing at each corner and in the center would allow you to tie the deck into the footing with some threaded rebar. Also, for options 3 and 4, consider doubling the center post, and using half length joists that meet in the center, with no notch. Also, consider bridging, or short blocks diagonally between adjacent joists. – Ben Mealey Sep 09 '21 at 22:49
  • Given material limitations, I'd space the joists more closely (~300mm OC, versus ~400mm) and be prepared to add two more beams underneath the quarter points of the joists. With all those beams, I'd add support to the ground at the edges and the middle. And, as noted by pretty much everyone, notching is not a good idea. – Aloysius Defenestrate Sep 10 '21 at 14:14
  • Spruce is a standard wood type for pressure-treated lumber (along with pine and fir). It is plenty good in terms of quality. No one* frames using hardwoods because it is too difficult to work with and too expensive. (* - some people who have more money than small countries use hardwoods) – TylerH Sep 10 '21 at 14:49

4 Answers4

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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isherwood
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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.

longneck
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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 09 '21 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 09 '21 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.

r13
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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 09 '21 at 21:02
  • @isherwood I don't see that's a problem. But OP likes your idea, so it must be it. :) – r13 Sep 09 '21 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.

isherwood
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Jasen
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    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 '21 at 14:11