Deck Ledger options? Direct VS standoffs VS Deck Brackets?
Ive got a few options on my ledger attachment and trying to decide the best route to go.
Zone 4 retrofit, new sheathing with 3″ polyiso exterior, rain screen siding. Large deck (8′ above grade) with wrap around porch
Option A: Common ledger board attachment over zip sheathing bolted into rim joist which is in the daylight basement and can be insulated from interior.
Option B: Double up some PT blocking to create 3″ standoffs for the ledger so there is less thermal break of the exterior foam. Was thinking 3′ o/c for those standoffs?
Option C: Maine deck brackets seem great but id need a fair amount of them so would be expensive.
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For possible moisture problems #1 is the most risky and hard to get right. It also makes replacing the decking very difficult. I would take it right off the table.
Either of the other two will work fine. if you go with #2, make sure to run it by your inspector first.
Don't forget about the requirement for hardware to resist lateral loads on the ledger.
If you can insulate at the interior and you aren't going for super high performance, I'd go with option A. If you get into standoffs you should really get engineering done, as the rotational forces on the blocks and ledger can get large. Maine Deck Brackets work well but most people seem to underestimate how many are needed, and that the ledger often needs to be doubled up as well.
Edit to add: Malcolm and I usually agree on details but this seems to be an exception. The IRC allows up to 1/2" space between sheathing and ledger: https://codes.iccsafe.org/content/IRC2018/chapter-5-floors#IRC2018_Pt03_Ch05_SecR507.9 but no more without engineering. I usually locate the WRB at the sheathing so flashing an "inset" ledger is just like normal, then the exterior insulation is treated more like part of the siding system.
I avoid decks when possible, partly because of these kinds of details, but people seem to like them. ;-)
Two things seem complicated to me with option #1, which as you say are related to the layers outside the sheathing.
- The bottom of the insulation, strapping, and siding above the deck will need protecting from both pests and splash-back while still maintaining a drainage plane for the cavity.
- Where on a typical installation the siding layers below the deck can just butt up to the ledger, both they and the 3" of insulation now need to be capped to stop water infiltration, and this protection (flashing) now needs to extend up the sides of the ledger where it ends.
I think it's asking a lot to get all that right.
I hate decks!
Good points, as usual, Malcolm. The recent projects where I've had this situation have not had siding below but foundations, so it hasn't been an issue. On other projects with decks and exterior insulation I've used Maine Deck Brackets or I've made the deck freestanding.
I suspect your advice presupposes better builders than the rest of us are accustomed to working with. That's what comes from hanging out with Ben Bogie et al.
I'm going for as high performance as possible on my limited budget. Doing most of the work myself and have bought most of the materials recycled/overstock. If I install a double ledger and flash it properly, that seems to be the easiest option without having to get an engineer to sign off on it and shouldn't compromise performance too bad if the basement is insulated from the interior right?
I attached a sketchup of what i was thinking too.
That works. You will need a similar profile flashing underneath that will extend out to cover the top of the siding and gap.
- Install the upper one before the deck joists so that the return gives continuous protection to the ledgers.
- Install the lower one after the first ledger is on, so it can be smaller.
- Make sure they both have a good slope, and end-dams.
- Don't forget the lateral load connectors. See page #18 in the attached guide.
If you look a the cut sheet for this, it can also be used for rigid insulation:
> Zone 4 retrofit, new sheathing with 3″ polyiso exterior, rain screen siding. Large deck (8′ above grade) with wrap around porch
Unrelated... curious how you ended up with 3" of exterior insulation in climate zone 4. Not sure you'll ever make the money back on that.
Edit: I see from a previous of your posts that it's recycled material, so my question is basically void, but I will leave this here for anyone else wondering as well.