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I'm gearing up to replace a deck that currently has 2x6 joists and same sized ledger. Is it best to remove the existing ledger board and replace it with a 2x8 so I can use 2x8 joists? Or is there a way I can retain the ledger and connect the larger sized boards? A larger ledger will of course mean extra work with trimming the siding, etc.

For info: I'm replacing PT decking with Trex. New 2x6 joists would meet my local code without problem, but it seems 2x8s are more advised.

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    As for joist size, it all depends on the length you're running, the spacing between them, and how much support you'll have underneath. Trex recommends 16" OC at most, 12" if running the boards diagonally. This is fine for 2x6 spacing. For the ledger, it's worth replacing so it's the same size. You might not be able to fully secure the larger hangers to the smaller ledger. Plus I couldn't find a single example online where someone used a smaller ledger, but plenty of photos of decks falling due to failed ledgers. Personally, I'd spend the extra $40 to replace the ledger if changing to 2x8s.
    – Phaelax z
    Commented Jun 29, 2021 at 13:30
  • @Phaelaxz, it's not a matter of $40, as was stated in the question. As is typical, a rework of the siding is also necessary. I'd be looking to avoid that as well.
    – isherwood
    Commented Jun 29, 2021 at 14:07
  • Don’t forget that the Code now requires at least 2 anchors mounted near each end of the deck fastening the deck to the house. Here’s one from Simpson: fastenersplus.com/…
    – Lee Sam
    Commented Jun 29, 2021 at 19:53

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With the right hardware you can probably reuse the ledger. If it's fastened to the structure by an approved means (lag screws no longer qualify), and if you use joist hangers that don't require fasteners near the bottom, it should work fine.

One other strategy, if 2x6 joists are indeed adequate, would be to simply notch the joists so that the mount height remains nominal 2x6 size. This will not negate the stiffness benefit of the larger joist size. I would then run two 3" screws from below and just outside the notch to prevent horizontal splits there.

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Of course, you could always break out a jigsaw and put a nicer tapered, curved transition outside the notch to relieve stress, a la the boards on a pergola.

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  • I'd think notching all those joists would be more time consuming than simply trimming an extra inch off the siding. But as he never stated the size of the deck I don't know how many he'd have to do.
    – Phaelax z
    Commented Jun 29, 2021 at 15:37
  • Apparently you've never retrofitted a ledger onto a building. I can assure you that the notches would be a fraction of the effort.
    – isherwood
    Commented Jun 29, 2021 at 15:52
  • I have, when I added a 24' carport to the side of my house years ago, it really wasn't that difficult. And your comment wasn't constructive in any way towards the question.
    – Phaelax z
    Commented Jun 29, 2021 at 16:08
  • Sure it was. I disagree wholeheartedly and wish to discourage anyone from taking your advice. I think my 15 years in the business trumps your carport.
    – isherwood
    Commented Jun 29, 2021 at 16:09
  • Carport was one example, want a resume of homes I've built? Just because you find a ledger board a difficult job doesn't mean it's hard for everyone. And generally, the ledger should match the size of the joists. 15 years experience you should know that.
    – Phaelax z
    Commented Jun 29, 2021 at 16:21
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You mention that 2x6 is minimum for load bearing, and 2x8 is recommended.

I'd guess that recommendation stems from the desire to have added stiffness in supporting the Trex boards.

In addition to the option to notch the 2x8 and use 2x6 hangers, you could use 2x6 with smaller spacing to increase stiffness.

If you currently space out at 16" OC, you could bring that down to 12"OC or less. As a rule of thumb, 2x8 spaced at "S" is roughly as stiff as 2x6 spaced at "S/2".

What quickly becomes clear is cost: 2x8 will be almost half the cost compared to the 2x6 option, considering lumber and fasteners (but free labour).

Personally I prefer the smaller spacing. Although the overall framing stiffness is the same, and exceeds code, for both options, each individual board -spanning less between joists- will deflect less when loaded by a person, reducing foot-drop vibrations.

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  • It's worth mentioning that smaller spacing requires more screws, which has a visual impact.
    – isherwood
    Commented Jun 29, 2021 at 15:54
  • @isherwood, yes indeed, but possibly mitigated with Trex hidden fasteners that use brackets. For PT wood I screw at 45 into side, and stagger left/right by joist so as to have same number of screws total. "clicking" from board bouncing off joist hasn't been a problem with one-sided staggered screwing
    – P2000
    Commented Jun 29, 2021 at 17:05
  • I'm thinking this is going to be the way to go. Although the deck is 24' in width, it will only end up being a few extra joists in the long run, so 12" makes sense (and I like the idea of going over code for my own peace of mind). Thanks for your comment!
    – user133918
    Commented Jun 29, 2021 at 21:39
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The best and easiest option is to mount a 2x8 directly to the existing 2x6 ledger board with 3 m10 or m12 3" screws top/middle/bottom every 16" on center. This is a common construction practice which I have detailed many times (I work at an architectural/structural firm).

You could also add some construction adhesive to glue the 2x8 to the 2x6 to increase the bond. I would also drill holes in the 2x8 to expose the ends of the fasteners securing the 2x6 to the wall.

Then you can hang your new joists on the new 2x8.

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    What wood screw would you use if you don't have access to the back of the 2x6 (existing ledger) for an M10 nut?
    – P2000
    Commented Jun 29, 2021 at 15:32
  • Lag screws. Or better yet, drill all the way through the 2x6 and attach to the framing behind it if you can
    – Phaelax z
    Commented Jun 29, 2021 at 15:38
  • Lag screws are not allowed for this application.
    – isherwood
    Commented Jun 29, 2021 at 15:53
  • "Since 2009, every edition of the IRC (including the anticipated 2021 edition) requires the deck ledger to be connected to the house floor band joist with ½" bolts or lag screws" I don't know how his existing ledger is attached, but this code leads me to believe lags are permitted.
    – Phaelax z
    Commented Jun 29, 2021 at 16:12
  • His ledger board is already attached to the house. He can add an additional board attached to the ledger and use lag screws as indicated. Using 1/2"x5" lag screws to screw through the existing ledger board and into the floor band would work and then the new 2x8 would be considered part of the ledger instead of just a board secured to the ledger.
    – Marmiketin
    Commented Jun 29, 2021 at 16:40

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