Deck Flashing That Works

Whether it’s wood or composite, here’s how to ensure that water drains away from the walls, ledger, and joists 

June 27, 2016
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Deck Cable Railing. Photo: Deckorators

Photo: Deckorators

In a video from Glenn Mathewson posted on about deck ledger code requirements, Glenn looks at a couple of good details, one from the EPA, the other from Building Science Corp. Glenn preferred the BSC detail, so I put it into an animation. This article uses stills from that animation.

The peel-and-stick membrane protects the wall, and the flared drip edge protects the ledger by directing water away from it. Don’t cut the flashing at each joist—it takes extra work and can cause wicking. Instead, hold the joists ¼ inch or so off the ledger, supported by the joist hanger. Choose a hanger with base support of 1½ inches, plus the gap. 

1 ] Apply peel-and-stick membrane over the base of the wall


2 ] Install Z-style ledger flashing with a hemmed drip edge


3 ] Select joist hangers one size down from the joist depth


4A ] Layer the housewrap over the ledger flashing


4B ] Install the joists, but don’t mash them against the ledger


5 ] The decking goes on top

About the Author

About the Author

Dan Morrison is senior technical editor of, a sister site to Professional Remodeler.



Looks water tight. However there is a problem when it comes to decking edge nailing where nails penetrate the flashing on the top of the ledger.

Thanks for the comment, Dan. I agree that it does look water tight and that there could be a problem, if people drive nails through the flashing.

I guess I figured that most folks could figure that out, but just to make sure, here's the addendum:

"Don't drive nails or screws through the edge of the first decking board to avoid making holes in your flashing (and injection channels into your deck joists)."


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