A deck ledger leak happens when water running down the house wall gets behind the board that attaches the deck to the house. Without flashing above the ledger, or when the ledger was bolted on over the siding, the rim joist and sill plate behind it stay wet and rot, and water can reach the basement ceiling below the door. Repairs involve removing siding behind the ledger, installing continuous corrosion-resistant flashing and reattaching the ledger with code fasteners. Integrity does not build or repair decks; this page explains what to look for so you can brief a deck contractor. It is general information.
On this page: Signs · Causes · Under-deck check · Fixes · Code basis · Who to call
Signs of a ledger leak
- Stains, rot or mold on the rim joist and sill plate inside the basement or crawlspace behind the deck.
- Water stains on the ceiling below the deck door.
- Rust streaks running down from ledger bolts.
- Soft, dark wood along the ledger or the siding just below it.
- A visible gap between the ledger and the house, or a ledger pulling away.
Why ledgers leak
| Cause | What happens |
|---|---|
| No flashing above the ledger | Water runs down the wall and straight behind the ledger |
| Ledger installed over the siding | Water trapped between the ledger, siding and sheathing |
| Aluminum flashing on copper-treated lumber | Flashing corrodes and fails |
| Door threshold not flashed | Splash and snowmelt run under the door into the floor framing |
| Siding run down onto the deck surface | Bottom edge wicks water |
A check from under the deck
- Look up at the top of the ledger. You should see metal or membrane flashing that runs up behind the siding and lips out over the ledger.
- Check bolt heads and the wood below them for rust streaks.
- Probe the ledger and the siding below it with a screwdriver for soft spots.
- Check for a gap between the ledger and the house.
- From inside, look at the rim joist area behind the deck with a flashlight.
Stop using the deck and call a deck contractor right away if the ledger is pulling away from the house or the wood around the fasteners is soft.
The correct fix, and the wrong ones
| Fix | When it fits |
|---|---|
| Add flashing above the ledger by removing the first deck board where possible | Short-term step when the ledger and rim are sound. |
| Support the deck, remove siding behind the ledger, install continuous flashing, reattach with code fasteners, re-side | Missing flashing, siding behind the ledger, or early rot. |
| Repair the rim joist and sill, then rebuild the connection | Rot has reached the house framing. |
| Rebuild as a freestanding deck | The house cannot properly support a ledger. |
Wrong fixes: caulking the ledger to the siding, adding more nails, aluminum flashing on copper-treated lumber, or attaching a ledger to brick, stone veneer or a cantilevered floor.
Code and guide basis
- Code. The 2021 IRC, section R703.4, requires flashing where exterior porches, decks or stairs attach to wood-frame walls or floors. Section R507.2.4 requires deck flashing to be corrosion-resistant metal at least 0.019 inch thick, or approved non-metallic material.
- American Wood Council, DCA 6 Prescriptive Residential Wood Deck Construction Guide. Siding must be removed before the ledger is installed; approved corrosion-resistant flashing is required at any ledger connection to a wood-framed wall; aluminum should not touch lumber treated with copper preservatives such as ACQ or copper azole; the door threshold must be flashed against splash and snowmelt; ledger attachment to brick, stone or masonry veneers, hollow masonry, cantilevered floors and bay windows is prohibited.
Water from a deck can soak the whole wall; see water behind siding. For deck materials in wildfire zones, see WUI siding and deck rules in Colorado.
Who to call
Integrity does not sell, build or repair decks, and the ledger, fasteners and framing belong with a licensed deck builder or structural contractor. Where the deck meets the house, Integrity can remove and reinstall siding and trim so your deck contractor can flash the ledger, and we can check the roof and gutters that drain onto the deck. See the exterior problems guide.
Book an exterior inspection
Integrity Roofing and Painting is veteran-owned and family-run since 1990, an Owens Corning Platinum Preferred contractor with 650+ Google reviews. Colorado Springs area: call (719) 488-2800 or book a free inspection. Denver metro: call (303) 209-0152 or book a free Denver inspection. Austin: call (512) 610-5897 or book a free Austin inspection. We reply the same business day.
Sources: 2021 IRC Chapter 7, section R703.4 (UpCodes); 2021 IRC Chapter 5, section R507.2.4 (UpCodes); American Wood Council, DCA 6 Prescriptive Residential Wood Deck Construction Guide.
