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Party walls, townhouse roofs, and R327
A party wall is a townhouse fire-separation, not a wildfire siding menu. Oregon’s 2023 R327 amendment adds R302.2.12 townhouse roof covering classes, and, where a municipality adopts R327 for wildfire hazard zones, points those roofs at R327 (amendment PDF). Exterior walls that face weather still have to meet R327.3.3 where that section is adopted. Those are stacked jobs. One listing does not finish both.
You are on a zero-lot-line drawing. One wall sits on the lot line. The other walls see the street and the yard. The lot-line wall is the R302 separation. The yard wall is the wildfire covering.
This page does not reprint 2023 ORSC R302.2.1 assembly figures. Those live in Chapter 3, which this session did not open as a full PDF. Read that chapter for the rated-wall options. Do not use a house-level hub graphic as a party-wall detail.
Why it matters
Townhouses share a wall. Fire-resistance rating under R302 is about the neighbor. Wildfire rules under R327 are about embers, flame, and the exterior. If you spec only R327.3.3 Type X behind cladding on the lot line, you may have a covering path and still miss the rated separation. If you spec only the rated wall and a Class C roof in a wildfire hazard zone that adopted R327, Exception 2 of R302.2.12 sends you back to R327.3.
ADU, garage, and shop is a different scope question. Manufactured dwellings are outside ORSC.
How the jobs split
| Job | What decides it | What it is not |
|---|---|---|
| Townhouse separation wall | ORSC R302 (Chapter 3) | R327.3.3 covering menu |
| Townhouse roof, generally | R302.2.12 Class C independent / Class B dependent, plus Chapter 9 | An automatic Class A |
| Townhouse roof in an adopted wildfire hazard zone | R302.2.12 Exception 2 → R327.3 | The small Class C exception |
| Exterior walls that face a yard or street | R327.3.3 and R327.3.3.1, where adopted | The party-wall rating |
| Alternate product | R104.11 | A hallway yes |
R327.3’s roof floor is a Class B-rated assembly equivalent. Wood shingles and shakes are not permitted. See covering versus assembly.
The paths
1. Rated separation (R302). Build the townhouse wall the Chapter 3 options allow. This page does not invent a 1-hour or 2-hour number from a 2021 excerpt. Open the 2023 ORSC chapter the official is using.
2. Roof class (R302.2.12). Structurally independent townhouses: minimum Class C covering. Structurally dependent townhouses: minimum Class B covering. Exception 1 lets some small, low, set-back dependent townhouses use Class C. Exception 2, where the municipality adopts R327 for areas it calls Wildfire Hazard Zones, sends those roofs to R327.
3. Wildfire roof (R327.3), when Exception 2 applies. Class B-rated assembly equivalent. Profile gaps closed, fireblocked, or ASTM D3909 cap sheet. Valley metal if a valley exists. See valley flashing.
4. Exposed exterior walls (R327.3.3). Noncombustible, ignition-resistant, heavy timber, log, or ASTM E2707. Type X behind the covering is a deemed-to-comply exception for that menu. See Type X behind the covering. Extent still runs foundation to roof.
5. California. CWUIC and California townhouse separation are a different stack. Do not import Oregon’s R302.2.12 split.
What people mix up
- Treating R327.3.3 as the party wall.
- Treating the party wall as a skip of wildfire covering on the yard elevations.
- Using Exception 1’s Class C roof in a wildfire hazard zone that adopted R327.
- Writing Class A because R327 said so. Oregon’s R327 floor is Class B-rated assembly equivalent.
- Pulling a manufactured home into this page.
How to check
- Confirm whether R327 is adopted for the lot, and whether the municipality named the area a wildfire hazard zone for Exception 2.
- Name independent vs dependent townhouse. That picks R302.2.12’s Class C or Class B floor, unless Exception 2 sends you to R327.
- Open 2023 ORSC Chapter 3 for the separation-wall options. Do not guess the rating from this page.
- Walk every exterior elevation that is not the lot-line separation. Those still need an R327.3.3 path where adopted.
- Put both the rated assembly and the wildfire covering on the drawings.
Limits
This page does not spec a GA file, an ASTM E119 listing, or a structural-independence detail. It did not open 2023 ORSC Chapter 3 as a full PDF. FireApproved is not the AHJ. CWUIC is a different book.
Related records
Questions
Does R327 replace the party wall?
No. Townhouse separation is ORSC R302 fire-resistant construction. R327, where adopted, is an additional wildfire section for dwellings and accessory structures. The 2023 amendment adds R302.2.12 roof covering classes and, in wildfire hazard zones where the municipality adopts R327, points those townhouse roofs at R327.
What roof class does a townhouse need?
R302.2.12, as amended, requires a minimum Class C covering on structurally independent townhouses and a minimum Class B covering on structurally dependent townhouses, plus Chapter 9. Exception 2 says that where the municipality adopts R327 for wildfire hazard zones, those townhouse roofs follow R327. R327.3’s floor is a Class B-rated assembly equivalent, and wood shakes are not permitted.
Is the lot-line wall an R327.3.3 covering?
The lot-line separation is the R302 fire-resistance-rated assembly. Exposed exterior walls that face a yard or street still have to meet R327.3.3 where that section is adopted. Do not treat Type X behind cladding as the party-wall rating unless the official accepts that stack for both jobs.
Does this apply to a manufactured home?
Manufactured dwellings are outside ORSC and R327. See the manufactured-homes finding. Townhouse rules on this page are ORSC buildings.