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Community and Q&A

Deck Ledger Flashing

Jeff_Garnelis | Posted in General Questions on

Hi all,

I am installing a deck on my house and was wonder how I should properly flash it. I plan on using the deck2wall spacers and holding the ledger off the house 1/2 an inch. Do I still need to run copper flashing behind the ledger? Can I get away with just installing a UV peel and stick membrane or just a couple layers of UV stable acrylic tape lapped correctly? My initial thought was to buy some 12in G-tape and run two rows with a 12inch overlap. My sheathing is 7/16 zip. Solid 2×12 rim joist.

Also, has anyone had any issues with the deck2wall spacers or does anyone have an argument for attaching the ledger directly to the house?

Thank you in advance. 



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  1. Expert Member


    Here is how I would flash it if you use the spacers:

    - Extend the WRB from the storey below up above where the ledger will sit.
    - Below the ledger, attach a pre-finished drip-edge flashing to divert the water away for the siding below. Form end-dams in the flashing.
    - Cover the area behind the ledger with a peel & stick membrane
    - Cover the membrane with a pre-finished flashing (doesn't have to be copper) that extends up several inches above the ledger. This is worth doing, as you will never have access to the area behind the ledger for maintenance or repairs.
    - Lap over the top of the flashing with the WRB from the story above.
    - Install your spacers, ledger, and the additional hardware necessary to resist horizontal loading. Bed anything that penetrates the flashing in caulking.

    All that said, I don't like spacing the ledger. I don't think it's a good idea to intentionally plan to drain water against the building envelope. Here is how I install ledgers:

    - Install a drip-edge flashing to protect the siding below, so that the vertical leg will be covered by bottom of the ledger.
    - Cover the area behind the ledger with a peel & stick membrane, lapping over the flashing.
    - Attach the ledger with lag screws, and the additional hardware necessary to resist horizontal loading.
    - Cover the top of the ledger with a drip-edge to divert water to the outside. The outboard leg of this flashing should sit flush with the outside of your ledger, and extend down 1 1/2". This leg will run between the ledger and the ends of the deck joists.
    - Lap the WRB above over the drip-edge flashing.
    - Install your joist hangers so that the top of your joists will sit 3/4" to 1" above the top of the ledger. This provides a drainage path for any water or debris that may accumulate against the house, diverting it out beyond the ledger.

    1. Jeff_Garnelis | | #2

      Thanks Malcolm. Few follow-up questions - 1. Do you have a recommendation for a peel and stick membrane? I don't want to by one that will leak on my siding below the deck. 2. Since I have Zip sheathing I do not have a WRB on top of my sheathing. Should I just add a layer of zip tape on the top edge of my peel and stick membrane? 3. Should the peel and stick be butyl or acrylic? I saw that pressure treated wood can cause issues for asphalt based membranes/tapes.

      1. Expert Member
        MALCOLM TAYLOR | | #3


        1. I have never found much of a difference between the rolls of peel & stick I have used and pick up whatever my lumberyard sells. Right now it's Resisto. Covered by flashing or siding, I have never had it deteriorate or leak.
        2. My hunch is the peel & stick will be fine without tape, but I don't know enough about Zip to recommend skipping the Zip tape.
        3. It depends on what PT you have there. We use MPS (MCA) now, which doesn't have those issues.

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