Deck ledger and the wall intersection

The ledger is the board that hangs an attached deck on the house. Where Oregon R327 is adopted, that joint is three code jobs, not one listing. The walking surface follows R327.3.5 when it sits greater than 30 inches and less than 12 feet above grade. The wall covering still has to meet R327.3.3 and run from foundation to roof under R327.3.3.1. The underfloor of an elevated structure is enclosed to grade or the exposed underside is protected under R327.3.4.4, which has no 12-foot exception (amendment PDF). FEMA P-737 treats the ledger as flashing against embers and water. It is guidance, not a fourth R327 subsection.

You are on the deck looking at the last board against the siding. That line is the ledger. Debris sits in the board gaps. Heat and embers collect in the corner where the walking surface, the wall, and the under-deck void meet.

The deck-to-wall drawing (DET-017) is not published yet. Read the code sentences and the FEMA table. Do not use a house-level hub graphic as this detail. Height bands for the walking surface and underfloor live on the 12-foot rule and on decking.

Why it matters

Embers and hot gases lodge under decks and in the gaps between boards. FEMA also says embers settle against exterior walls and accumulate at railing edges. Ignition at the ledger is ignition of the house wall, not only of a few boards. A listed walking-surface product does not close that corner by itself.

IBHS Wildfire Prepared treats an attached deck as part of the building footprint. The 0–5 foot noncombustible zone is measured from the outermost posts. That is a designation standard. It is not Oregon R327. IBHS does not replace adopted code.

How the joint works

Four objects share one line on the drawing.

The 30-inch to 12-foot band is walking surfaces only (R327.3.5). Do not write that band onto R327.3.4.4. Deschutes County’s public FAQ is blunt. Elevated-deck undersides have no 12-foot out. Stairs to those decks are a BCD exemption in that FAQ. See the stairs finding.

The paths

1. Walking surface (R327.3.5). Where the height band applies, pick one numbered material path. ASTM E2632 plus ASTM E2726 is item 1. Ignition-resistant material tested to ASTM E84 or UL 723 is item 2. Exterior fire-retardant-treated wood is item 3. Noncombustible is item 4. Items 5 and 6 are E2632 paths that also require the exterior wall covering to be noncombustible or ignition-resistant. That is why the wall at the ledger is not optional on those paths. The 200 square foot nominal 2-inch lumber exception is a walking-surface exception. It is not an underfloor skip and not a wall skip. Full menus live on decking.

E2726 is the upper-surface brand method. ASTM withdrew it in 2026 with no replacement. Oregon’s 2023 amendment still names both numbers. Read the adopted section and the test reports. Do not treat an OSFM 12-7A-4 row as an automatic R327.3.5 pass. A named Trex model in handbook category 8110 is a California BML record, not one listing for the brand. See the Trex finding.

2. Wall covering at the house (R327.3.3 and R327.3.3.1). The deck does not stop the wall. Covering still runs from the top of the foundation to the roof. At an open overhang it dies into 2-inch nominal blocking. At an enclosed eave it dies at the underside of the enclosure. See wall covering termination. Type X behind the cladding is one deemed-to-comply wall path. See Type X behind the covering.

FEMA’s retrofit language at this wall is different from R327. If existing siding is combustible, the guide says replace the bottom two to three courses with noncombustible siding, or install metal flashing extending 18 inches from the top of the deck, tucked behind the siding. That is FEMA best practice. It is not an Oregon subsection.

3. Underfloor (R327.3.4.4). Enclose to grade in accordance with the section, or protect the exposed underside with the numbered menu (noncombustible, ignition-resistant, 5/8 inch Type X behind a covering, the exterior of a 1-hour wall assembly, or ASTM E2957). Heavy-timber columns and beams are excepted. Mesh laid horizontally under the boards is the installation mistake. If you screen, close the vertical opening from the walking surface to grade. See the under-deck mesh finding.

4. Ledger flashing (FEMA, not R327). FEMA says install flashing on ledger boards that are attached without gaps, as a barrier to embers and to water. For a partial decking replacement, replace combustible boards parallel to and within one foot of the adjacent exterior wall with noncombustible decking. Gaps between new walking-surface boards should be 1/8 inch or less in that guide. Larger gaps let debris and embers through.

5. IBHS footprint and the six-inch band. Attached decks get their own 0–5 foot noncombustible zone, measured from the outermost posts. Exterior walls, and combustible posts, need at least six inches of noncombustible covering measured from grade and from the nearest horizontal surface, including decks. Under an elevated deck, vegetation and combustible groundcover come out to mineral soil or noncombustible hardscape. When the walking surface is four feet or less above the ground, IBHS encloses the outer edge with noncombustible corrosion-resistant mesh not exceeding 1/8 inch. That four-foot mesh height is IBHS. It is not R327.3.4.4.

6. California. CWUIC Chapter 5 is a different book. Do not import Oregon’s walking-surface band or underfloor menu without reading it. CAL FIRE’s home-hardening page treats the area under the deck footprint and five feet out as an ember-resistant zone. See Zone 0 in California, Oregon, Firewise, and IBHS.

What people mix up

• Treating the ledger as its own R327 fire section.
• Writing the 30-inch to 12-foot band onto the underfloor rule.
• Writing IBHS’s six-inch wall band onto R327.3.3.1.
• Calling a listed deck board the whole joint, including the wall and the void.
• Stapling mesh under the boards at the ledger line.
• Leaving a gap at the ledger for “ventilation.”
• Treating a fence that hits the same wall as a deck problem. That is a wick. See fence as a wick.

How to check

1. Confirm R327 is adopted for the lot. If it is not, the Oregon sentences do not bind. IBHS and CAL FIRE can still apply as designation or guidance.
2. Measure the walking surface to grade or the surface below. Write the height on the drawing.
3. Name the R327.3.5 path, including whether that path requires the wall covering to be noncombustible or ignition-resistant.
4. Confirm the wall covering continues behind and above the ledger and still has an R327.3.3 path. Put the termination on the drawings.
5. Look at the ledger. FEMA wants flashing and no gap at that board. Confirm with the official what they will stamp.
6. Look under the deck. Enclosed to grade or a protected underside. No 12-foot out. No horizontal mesh under the boards.
7. Walk the five-foot band from the outermost posts, including under the deck. Inorganic ground. Not bark.

Limits

This page does not size ledger bolts, laterals, or flashing laps for weather. It does not pick a board SKU. It does not rate a composite brand. DET-017 is not published. FireApproved is not the AHJ. R327, where adopted, is a new-construction code. FEMA P-737 is a builder guide. IBHS is a designation.

Related records

• Decking, siding, landscaping
• The 12-foot rule
• Wall covering termination
• Type X behind the covering
• Fence as a wick
• ASTM E2632, ASTM E84, SFM 12-7A-4
• Under-deck mesh