Flashing a Deck Ledger Board on Vinyl Siding

Here's the right way to do it

Attaching a deck ledger board to a vinyl-sided house requires a few extra trim pieces to keep water from leaking behind the siding. Here's a rundown of the materials and procedure.

By the DIY experts of The Family Handyman Magazine

Installing the flashing

Start by making an outline on the siding where you want to position the ledger board. Make the outline large enough to include space for the deck boards on top, the ledger and any trim boards on the sides. Then cut away the siding.

Nail undersill trim (J-channel will also work) over the bottom cut, using 11-gauge aluminum nails. It's a tight fit to drive the nails into the undersill, but you can gently pull back the siding, then tuck it into the undersill after you nail it. If necessary, remove a few pieces of siding, nail the undersill, then replace the siding.

Tack Z-flashing over the channel, extending it slightly past the cutout on both sides. If you need two or more pieces of flashing, overlap the joints by 4 in. and seal with silicone caulk. Avoid using galvanized flashing with ACQ treated lumber because it can cause corrosion.

Nail J-channel along both sides of the cutout. Then tack the ledger into place with 16d nails. Next, slide drip flashing behind the vinyl so the lip fits over the top of the ledger as shown at right. Install undersill trim along the edge of the vinyl, over the flashing at the top and bottom.

Then lag-screw the ledger to the house using the fastener pattern approved in your plan. A building inspector we talked to said that incorrectly installed ledgers are the main cause of problems in do-it-yourself decks because the ledger may pull loose from the house. Make sure to get a building permit before starting a deck project so the inspector can check the ledger installation. It's extremely important for the ledger to be firmly attached.

Finally, caulk around the bolt heads to seal the holes against moisture.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Miter saw
  • Cordless drill
  • Circular saw
  • Socket/ratchet set
  • Level
  • Drill bit set
  • Framing square
  • Safety glasses
  • Utility knife
  • Tin snips

You'll need a zip tool to remove vinyl siding.

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

  • Undersill trim
  • J-channel
  • Aluminum nails
  • Z-flashing
  • Drip flashing
  • Silicone caulk
  • Bolts
  • Ledger board