Skip to content
CrossBeamStart a pre-check

Building Code Reference

Got a CRC R507.9 correction?

Deck ledger flashing

For builders in California, Greater Seattle, the Las Vegas area, the Denver area and Kansas City · CrossBeam Permits

What this code requires, how to fix it, and how cities and counties review it

What this code requires

CRC R507.9 requires deck ledger boards attached to a house to have corrosion-resistant flashing at the ledger-to-wall connection. The flashing must cover the top edge of the ledger, extend up behind the wall cladding, and integrate into the weather-resistive barrier (WRB) so water can’t get behind the ledger into the framing. Without proper flashing, water infiltrates the wall cavity and causes rot in the rim joist, band joist, and structural framing. Most residential deck permits and ADU deck additions get flagged here when the flashing detail is missing from the plans or the WRB integration isn’t shown.

How to fix it

  1. Add a ledger flashing detail to the plan set

    Include a dedicated detail drawing — typically at 1-1/2" = 1’-0" scale or larger — showing the ledger board, the flashing, and the wall assembly. Label the flashing material. CRC R507.2.4 requires corrosion-resistant metal flashing at least 0.019 inch thick, or an approved compatible nonmetallic material; self-adhered membranes must meet FGIA 711. Show the flashing extending at least 2 inches up the wall above the ledger, and either 4 inches out past the ledger face or to the face and 1/4 inch down it (R507.9.1.5). This detail is what the plan-checker needs to approve the flashing design.

  2. Show flashing integration with the weather-resistive barrier

    The flashing must lap into the WRB — house wrap, building paper, or equivalent — not just sit on top of the siding. Show this clearly in the detail: the vertical leg of the flashing goes behind the cladding, and the WRB laps over that leg by at least 2 inches (or the full leg height, if less) and continues behind the flashing and ledger. Self-adhered flashing membranes are typically applied directly to the sheathing and lapped under the WRB above and over the WRB below. Show the lap direction with an arrow or note. If the existing WRB can’t be accessed without removing siding, note that the applicant will expose the WRB at the ledger attachment area and install flashing per the approved detail before reinstalling the cladding.

  3. Address bolt holes and fastener penetrations

    Each through-bolt or lag screw that attaches the ledger to the rim joist is a water intrusion point. Show in the detail — or call out in a note — that fastener holes will be sealed. Common approaches: self-adhered flashing membrane with slit cuts that seal around the bolt, or field-applied sealant at each fastener location. The plan doesn’t need to specify every bolt location, but it does need to show the method for sealing penetrations. Plan-checkers look for this because unsealed fastener holes are the second-most-common path for water behind a properly flashed ledger.

  4. Handle transitions near windows and doors

    If a window or door opening is less than 2 inches above the ledger, the flashing must extend to the bottom of that opening. If the ledger runs within 24 inches of a window, door, or any other wall opening, add a note or detail showing how the ledger flashing connects to the opening’s flashing. The WRB at openings is typically the pan flashing or sill flashing of the window — your ledger flashing needs to lap that system, not terminate in a gap. Show a plan view or elevation calling out the transition at openings. If no openings are nearby, a note confirming that is sufficient.

  5. Document the flashing material specification

    Call out the flashing product on the detail or in the material schedule. Galvanized flashing used with ACQ pressure-treated lumber (the standard deck material in CA) must be hot-dip galvanized or stainless — not electroplated zinc. ACQ treatment is corrosive to standard galvanized and to aluminum flashing. If you’re using a self-adhered membrane product, list the product name or spec (e.g., “Grace Vycor Plus or equivalent, min. 4" vertical leg”). The plan-checker will verify the material is compatible with the lumber treatment.

  6. Confirm corrosion resistance of all flashing fasteners

    R507.2.4 requires corrosion-resistant flashing, and its fasteners should be just as durable. If you’re using metal flashing, any nails or screws holding the flashing in place also need to be corrosion-resistant — stainless or hot-dip galvanized. Add a note on the detail: “All flashing fasteners to be hot-dip galvanized or stainless steel.” It’s a small item but inspectors catch mismatched fasteners at rough framing inspection, and correcting it after the cladding is back on is expensive.

  7. Resubmit with a plan-check response letter

    When resubmitting, include a written response to the corrections letter that references each flagged item by number and identifies where in the revised plans the correction appears. For R507.9, write something like: “R507.9 ledger flashing detail added at Sheet A-3, Detail 4. Flashing material specified as 20-gauge galvanized steel, G90 minimum. WRB integration shown at Detail 4A.” This gets the plan-checker to the right sheet in 10 seconds instead of hunting through the package.

Take the CRC R507.9 fix steps with you

All 7 steps in one email, so you have them on site instead of on this page.

Why you got flagged

Plan-checkers flag R507.9 when the ledger flashing detail is either missing from the permit drawings or doesn’t show how the flashing ties into the existing wall assembly. The most common scenario is deck plans that show the ledger board and bolt pattern but leave out any note or detail about flashing material, dimensions, or how it laps into the house wrap or building paper behind the siding. The plan-checker can’t verify code compliance from a note that just says "flash per code" — they need a detail.

A second common trigger is plans that show flashing but don’t address the intersection with windows or doors near the ledger. Where a deck ledger runs adjacent to a window or sliding door, the flashing has to work with the window flashing system. If the plans don’t detail that transition, plan-checkers will flag it because improper flashing at that junction is one of the leading causes of water-damage callbacks.

The third scenario comes up on remodels and additions where the existing wall has a hard cladding like stucco or fiber cement. The applicant shows a ledger on a stucco wall but doesn’t show the saw-cut reveal, step flashing detail, or how the new flashing integrates with the existing WRB that’s already behind the stucco. Stucco is not a WRB substitute — there has to be a continuous barrier behind it, and the ledger flashing has to connect to that barrier, not just lap the stucco surface.

A fourth scenario applies to decks being added to existing structures under a building permit. When the original structure was built without a ledger in mind, the WRB may not extend to the framing location where the ledger will attach. The deck plans need to show how the applicant will access and tie into the WRB, or document an alternate water management method acceptable to the jurisdiction.

The official code

CRC R507.9 Vertical and Lateral Supports at Band Joist (ledger flashing, R507.9.1.5), 2025 California Residential Code, Building Standards Commission

Read the source →

Common questions

What flashing material is required for a deck ledger under CRC R507.9?
CRC R507.9 requires corrosion-resistant flashing — it doesn’t mandate a specific product, so you have options. Hot-dip galvanized steel (G90 minimum), stainless steel, copper, and self-adhered flashing membranes all meet the requirement. The catch is material compatibility: if you’re using ACQ pressure-treated lumber (which is standard for deck framing in California), you can’t use aluminum flashing or standard electroplated zinc — ACQ is corrosive to both. Hot-dip galvanized or stainless are the safe bets with ACQ lumber. Self-adhered membranes like butyl-based products are also widely accepted because they seal around fasteners as well as covering the top of the ledger.
Does R507.9 require flashing on a freestanding deck that doesn’t attach to the house?
No. R507.9 specifically applies to ledger boards attached to the structure — the flashing requirement exists because the ledger-to-wall connection creates a water infiltration path into the wall cavity. A freestanding deck has no ledger attached to the house, so R507.9 doesn’t apply. You still need to follow R507 for the deck framing, post bases, and connections, but the ledger flashing section is not triggered. If your deck transitions from freestanding to attached (for example, a gate or handrail that ties into the house wall), check with the plan-checker whether that attachment triggers R507.9.
How far up the wall does ledger flashing need to extend?
CRC R507.9.1.5 requires the flashing to extend at least 2 inches vertically above the ledger, but standard practice — and what most plan-checkers expect to see on a detail — is a minimum 4-inch vertical leg behind the cladding, integrating into the WRB. The goal is to create a shingle-lap effect: water that runs down the wall hits the vertical leg of the flashing and is directed outward over the face of the ledger rather than behind it. Some jurisdictions reference IRC flashing tables that show a 4-inch minimum. Show the dimension on your detail; 4 inches is widely accepted and gets approvals.
Can I use house wrap as the only water protection behind a deck ledger?
No. House wrap (or building paper) is the WRB, not the flashing. R507.9 requires flashing in addition to the WRB. The flashing handles the direct water at the ledger-to-wall junction; the WRB handles incidental moisture in the wall cavity. Both are required and they work together — the flashing laps into the WRB so the whole system drains outward. Relying on house wrap alone at the ledger joint doesn’t meet R507.9 because house wrap isn’t rated for the concentrated water exposure at a horizontal ledger seam.
My deck is attaching to a stucco wall — how do I show ledger flashing on stucco?
Stucco walls are a common source of R507.9 corrections because the detail is more involved than on a wood-clad wall. You need to show a saw-cut reveal in the stucco at the top of the ledger location, installation of self-adhered flashing membrane or metal step flashing into the reveal and behind the existing WRB, and then reinstallation of the stucco at the base of the cut. The key is connecting the new flashing to the WRB that exists behind the stucco coat — stucco itself is not a WRB. Your plan detail needs to show the saw-cut depth, the flashing product, and how it laps under the WRB above.
Will the inspector check the ledger flashing before I frame the deck?
Yes, in most California jurisdictions a framing inspection happens before decking is installed, and many inspectors specifically look at the ledger flashing at that stage. The better practice is to schedule a ledger-only inspection before you start framing the rest of the deck. Get the inspector out to sign off on the flashing while it’s fully visible. Once the joists are in, the top of the ledger flashing is harder to verify. Some AHJs require a separate waterproofing or sheathing inspection before framing proceeds — check with your local building department at permit issuance.

Related corrections

Check my plans for this →