How to Flash a Deck Ledger Board
If you cut out your siding to install a ledger board, careful steps must be taken to ensure that moisture cannot reach your house. Infiltrating rainwater can travel downward, sideways and even upward, so special flashings must be used. In the past, metal flashing and extra layers of roofing felt (tar paper) were often used, but nowadays, vinyl “Z” flashing and rolls of vinyl back flashing do a better job.
Ideally, the house’s sheathing should be triple protected from moisture - with building paper or roofing felt stapled to the sheathing; then with back flashing; and then the Z flashing, which also protects the ledger itself.
The flashing configuration shown in this article is quite common. However, your codes may call for other methods, so check with your building department before you start work. For instance, some inspectors may prefer self-adhering flashing (which is much the same as self-stick ice and water shield often used at roof eaves) instead of vinyl back flashing.
It's dangerous whenever using a razor knife. Be sure to clamp a straight edge to the surface to ensure a straight line. This is just a score, not a cut. You do not want to cut through the flashing. Cutting halfway through will allow it to bend very easily.
In this example, we used back flashing that is as wide as the exposed building paper, plus 3". Mark for cutting to length with a square and pencil, and cut with tin snips. To make a bend at an inside corner, clamp a straight edge onto the piece and score with a knife, and bend carefully.
Slip the back flashing under the siding at least 3" at the top and the sides. You may need to pry out siding first. If nails are in the way, pull them out. Pry the siding out near a nail, then push the pry bar against the nail as you partially tap the siding back in. That should pop the nail head out far enough so you can pry it out. Take care not to tear the building paper or tar paper while you do this. Attach the back flashing with as few nails as necessary to keep it lying flat.
[TIP]
At this point, you will need to go to here to cut and attach the ledger. Then, come back and install the Z flashing.
[Tip] When nailing your vinyl Z flashing to the house, be sure to nail every 12" along the house with roofing nails. The nails should not be nailed tight to the flashing. You should allow the flashing to move from side to side in the slotted hole provided. Do not notch the flashing around joists.
At an inside corner, slide the first piece in so its bottom lip slips in between the two boards. (If the boards are too tight and you cannot do that, cut the lip to fit.) Snip a notch out of the second piece as shown, and slip it into place. If the second piece cannot sit flat, you may need to cut the notch a bit larger.
To keep water and ice from building up between the first deck board and the flashing, use an EPDM foam, such as Trex RainEscape Wall Flash.
Attaching the Ledger Board to the House Rim
Learn how to properly install a waterproof ledger board using flashing and fasteners. Check out our step-by-step video and detail drawings.
Attaching the Ledger Board to Brick Siding
Do you have brick siding? You should never attach to just the brick. This is very dangerous.
Removing the Siding
Learn how to cut and remove aluminum, vinyl, wood and cement board siding for installing a deck ledger board to a house wall.
Pressure Washer Buying Guide
When it comes to cleaning your deck, it's important to choose the right pressure washer. Use this pressure washer buying guide from Decks.com to help with your decision!
What is Wet Rot and How Do You Treat It?
Wet rot occurs when water or high moisture levels cause wood to decay. Learn how to recognize the signs and causes of wet rot and how to treat it.
How to Clean Outdoor Patio Cushions
Keeping your outdoor furniture cushions clean helps extend their life and makes your deck or patio area look nice. Learn how to clean outdoor cushions.
More Helpful Resources
Explore Articles by Topic
Footings
Information related to installing frost footings for decks
Framing
Learn structural framing methods
Decking
Learn about wood and composite decking materials
Stairs
An in-depth look at the complex issue of how to build stairs
Railings
How to install guardrails and handrails to meet IRC code
Features
An overview on water drainage, benches, planters and lights
Design
The basics of deck design
Planning
Learn about permits and working with contractors
Porches & Patios
Build a covered deck to enjoy all seasons
Ledger
Proper attachment techniques
Care
Maintain your deck to maintain your investment
Materials
An overview on water drainage, benches, planters and lights
what if my deck has no flashing
Our inspector discusses what you should do if you deck ledger board isn't properly flashed.
Attaching the Ledger Board to a Concrete Wall
Step-by-step instructions on how to install a ledger board to a concrete house foundation wall using expansion anchors.
Checking House Framing
Make sure your house frame is solid and in good condition before installing a deck ledger board. We list some problem areas to look for before building.
How to Remove Scuffs and Scratches from Composite Decking
Removing scuffs and scratches can help make your composite deck look like new. Learn how to fix and prevent your composite deck from future scratches.
How to Ink Stamps from Pressure Treated Lumber
Ink stamps seen on pressure treated wood represents where the lumber came from and its grade. Learn a few tricks to remove this ink from your wood at Decks.com.
How to Restore & Refinish a Deck
Decks need maintenance. A twice-yearly cleaning is needed at a minimum. But wood decks—even with good upkeep—can still warp, rot, or get termites. Plus, no stain or paint job lasts forever. Fortunately, you can reset the clock by restoring your deck and refinishing it.
Explore Articles by Topic
Footings
Information related to installing frost footings for decks
Framing
Learn structural framing methods
Decking
Learn about wood and composite decking materials
Stairs
An in-depth look at the complex issue of how to build stairs
Railings
How to install guardrails and handrails to meet IRC code
Features
An overview on water drainage, benches, planters and lights
Design
The basics of deck design
Planning
Learn about permits and working with contractors
Porches & Patios
Build a covered deck to enjoy all seasons
Ledger
Proper attachment techniques
Care
Maintain your deck to maintain your investment
Materials
An overview on water drainage, benches, planters and lights