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Roof-to-wall transitions and dormer cheeks
A dormer cheek is a wall that meets a roof. Where Oregon R327 is adopted, those are two sentences. The roof has to be equivalent to a minimum Class B-rated roof assembly under R327.3. The cheek is exterior wall covering under R327.3.3, run to the roof under R327.3.3.1 (amendment PDF). FEMA P-737 says flash where a roof abuts a wall, such as a dormer wall. An ASTM E108 class does not do that flash.
You are looking at the dormer from the yard. Needles sit in the cricket and along the step flashing. The cheek siding dies into the shingles, or it stops short and leaves a raw band. That line is the joint.
The roof-to-wall drawing (DET-014) is not published yet. Read the two code sentences and the FEMA flashing row. Do not use a house-level hub graphic as this detail.
Why it matters
FEMA says a roof with valleys and roof-to-wall intersections, where leaves and needles collect, has a greater ignition risk than a simple roof. Joints, abrupt geometry, and elevation changes accumulate debris. Embers that sit in that cricket are sitting against both the roof deck and the wall cavity.
A Class A or Class B letter on the shingle bag does not close the cheek. Class attaches to a tested covering-on-deck. See covering versus assembly.
How the joint splits
| Piece | What decides it | What it is not |
|---|---|---|
| Roof covering on deck | R327.3 Class B-rated assembly equivalent | The wall path |
| Profile gaps under tile or metal | Closed, fireblocked, or ASTM D3909 cap sheet | Valley metal |
| Valley, if the roof has one | 26-gage galvanized over 36-inch D3909 | Sidewall flashing |
| Dormer cheek | R327.3.3 wall menu and R327.3.3.1 extent | The gable-end overhang exception |
| Where roof abuts wall | FEMA flashing at the abutment | An E108 listing ID |
Wood shakes and wood shingles are not permitted where R327.3 applies. See the wood-shake finding.
The paths
1. Roof (R327.3). Asphalt, slate, metal, or tile per Chapter 9, or other roofing the building official deems equivalent to a minimum Class B-rated roof assembly. IBHS Essential still asks for Class A. Spec Class A if you need both. How to read an 8180 row lives on how to read a Class A roof listing.
2. Profile gaps. Where the roof profile leaves a space between covering and deck, R327.3 says construct it to prevent flames and embers, fireblock it, or install one layer of minimum 72-pound mineral-surfaced nonperforated cap sheet complying with ASTM D3909 over the combustible decking. That sentence is not the valley stack and not the sidewall flash.
3. Valley, if present. Separate sentence, separate guide. Valley metal and cap sheet.
4. Cheek as a wall (R327.3.3 and R327.3.3.1). Noncombustible, ignition-resistant, heavy timber, log, or an ASTM E2707 assembly. Type X behind the covering is a deemed-to-comply exception. Covering still runs to the roof. See wall covering termination. R327.3.4.1 Exception 2 (gable-end overhangs) does not skip the covering on the cheek itself.
5. Abutment flashing (FEMA). Install flashing where a roof abuts a wall, such as a dormer wall, at valleys, at skylights, and along rakes and eaves. FEMA’s valley metal numbers match Oregon’s 26-gage over cap sheet. The sidewall instruction is “flash the abutment.” It is not a second valley recipe. Confirm the metal with the official.
6. Eave of the dormer. If the dormer has an eave or soffit under 12 feet, the underside menu still applies. Fascia and architectural trim are excepted. See Craftsman eaves and the fascia finding.
7. California. CWUIC 504.2 is a Class A roof assembly, with named exceptions. That is stricter than Oregon’s Class B floor. Do not import Oregon’s roof sentence onto a California dormer without reading Chapter 5.
What people mix up
- Treating an E108 class as the sidewall flash.
- Calling the dormer cheek a gable-end overhang exception.
- Using the valley 26-gage stack as if it were automatically the step flashing.
- Stopping the cheek siding short of the roof and calling the gap “trim.”
- Writing Class A on the drawing because R327 said so. Oregon’s floor is Class B-rated assembly equivalent.
How to check
- Confirm R327 is adopted for the lot.
- Name the roof assembly, not a bag of shingles. If you use a listed model, put the listing ID on the drawing.
- Look at every roof-to-wall line, including dormer cheeks, chimneys, and parapets. Find flashing. Find debris traps.
- Confirm the cheek has an R327.3.3 path and that the covering hits the roof, not a raw band.
- If there is a valley, check the valley stack on its own page. Do not merge it with the cheek.
Limits
This page does not spec step-flashing laps, cricket geometry, or ice-and-water. It does not convert an E108 report into a wall listing. DET-014 is not published. FireApproved is not the building official. FEMA P-737 is a builder guide. IBHS is a designation.
Related records
Questions
Does a Class A or Class B roof listing include the dormer cheek?
No. ASTM E108 and UL 790 classify a roof assembly of covering on deck, under the conditions in the listing. They do not flash the wall. The cheek still needs an R327.3.3 wall path where that section is adopted.
Is a dormer cheek a gable-end overhang exception?
No. R327.3.4.1 Exception 2 names gable-end overhangs and roof-assembly projections beyond an exterior wall other than at the lower end of the rafter tails. The cheek itself is a wall. Treat it as R327.3.3, not as that eave exception.
Can I use the valley 26-gage stack as the roof-to-wall flashing?
The valley sentence is for valleys. FEMA separately says install flashing where a roof abuts a wall, such as a dormer wall. Do not assume the valley recipe is the sidewall recipe. Confirm the metal with the official.
Does Oregon require Class A at a dormer?
Where R327 is adopted, the roof floor is a Class B-rated assembly equivalent. IBHS Essential and many HOAs still ask for Class A. Spec Class A if you need both. Do not tell the official that R327 requires Class A.