The 12-foot rule

Oregon R327, where adopted, uses 12 feet as a height threshold, not as a pass for the whole house. Eave, soffit, and cornice vents are blocked on the underside unless the building official accepts a manufactured ember- and flame-resistant vent, or the opening is 12 feet or more above grade. Underside protection also applies when any portion of the eave framing is under 12 feet. Elevated-deck undersides have no 12-foot out.

You are measuring from grade to the lowest eave framing, not to the ridge. Twelve feet is a height trigger. It is not a pass for the whole house.

These numbers live in the adopted code. They are not a California CWUIC detail you should copy, not a Colorado CWRC 404.2 skip, and not an IBHS skip. See Oregon R327 versus California CWUIC.

Why it matters

Embers and heat collect under eaves and decks that sit close to grade. Deschutes County’s R327 FAQ calls the exposed underside of rafter or truss eaves, and enclosed soffits under 12 feet, a vulnerable area. A house can clear the vent rule and still fail the underside-covering rule. The reverse is also true. Height is not a skip for gable vents, crawlspace vents, or the deck walking surface.

If you treat “the house is 12 feet tall” as one exception, you will leave an ordinary soffit louver under 12 feet, or an open elevated deck, and call it done.

How it works

R327 splits the overhang into two jobs.

1. A hole in the underside is a vent. Embers go through holes larger than the mesh, and through gaps beside the frame.
2. The underside itself is a horizontal projection. Flame and heat from below can ignite that assembly even when there is no vent.

Twelve feet is a height proxy in the Oregon text, measured to grade or the surface below. For vents, measure to the opening. For underside protection, the trigger is any portion of the rafter or truss framing. Those are different tape-measure points. Write both on the drawing.

California’s live book is CWUIC, Title 24 Part 7 (people still search Chapter 7A). CWUIC 504.3 protects enclosed eaves. 504.10 names vent rules. Those sections do not use Oregon’s 12-foot eave-vent exception as the path. IBHS Wildfire Prepared Essential scores mesh or a listed vent. Enhanced wants enclosed eaves of noncombustible material, including outlookers, fascia, and decorative features. Neither IBHS level is a 12-foot rule. IBHS does not replace adopted code.

The paths

Where R327 is adopted, pick the path the section named. Confirm with the local department. Start with the BCD wildfire page.

1. Eave, soffit, and cornice vents (R327.3.2.1). Do not put ventilation openings on those undersides.

Exceptions:

1. The building official may accept vents manufactured to resist flame and burning embers. That is the performance path. On this site those models live under vents (OSFM category 8165 / ASTM E2886), not 8160.
2. Openings that already meet R327.3.2 (1/16–1/8 inch mesh, or a vent designed to resist embers and flame) may sit on that underside when the opening is 12 feet (3658 mm) or more above grade or the surface below. That is the prescriptive path only when the opening is high enough.

R327.3.2 still covers other ventilation openings that exist. Gable and crawlspace openings are not subsection 3.2.1. They still need mesh or a listed vent. Mesh versus a listed assembly is a different choice. See mesh versus listed vents.

2. Underside of eaves and soffits (R327.3.4.1). If any portion of the rafter or truss framing is less than 12 feet above grade or the surface below, protect the exposed underside. The menu is noncombustible material, ignition-resistant material, 5/8 inch Type X gypsum behind the covering, the exterior of a 1-hour wall assembly, or an ASTM E2957 soffit assembly. Those two material words are not synonyms. See ignition-resistant versus noncombustible. Full covering paths live on eaves.

The 12-foot exception here is stricter than the vent exception. All framing members must be 12 feet or more above grade, and 2-inch nominal eave fireblocking must run from the wall top plate to the underside of the roof sheathing. Gable-end overhangs and fascia or architectural trim are excepted in the code text (amendment PDF).

3. Other 12-foot lines, not the same test.

Architectural trim boards are excepted on patio ceilings and floor projections. Heavy-timber columns and beams are excepted on the elevated-deck underside. The walking-surface menu, including the 200 sq ft nominal 2-inch lumber exception, lives on decking. Do not copy the eave 12-foot exception onto that page.

Deschutes County’s public FAQ is blunt on decks. R327.3.4.4 contains no 12-foot exception for the underside of elevated structures. Covers over those decks still need protection when they are 12 feet or less from the walking surface below. Stairs to those decks are a BCD exemption in that FAQ. Read the FAQ. Do not invent a stair rule.

4. Unvented attic. Deschutes lists three attic and crawlspace options. Unvented attic or unvented crawlspace. Place allowed openings 12 feet or more above grade. Or use products manufactured to resist ember intrusion. Unvented is a ventilation design choice, not a 12-foot measurement. Remaining dryer, mechanical, gable, ridge, and crawlspace openings still need their own path. It is not foam in an existing vent. See unvented attic.

5. What you actually spec. A listing number is a model, not a brand, and not a permit. Deschutes County accepts OSFM handbook products when they are shown on the drawings. See show the product on the drawings.

Oregon names ASTM E2957 for a tested soffit. It does not name SFM 12-7A-3. Many California handbook 8160 rows name 12-7A-3. That is a different test method on a different book. Listing remains voluntary for most WUI products. Absence from the handbook is not an automatic ban. Presence is not an automatic permit. See OSFM listing is usually voluntary.

Example listed eave and soffit vents on this site (confirm the live listing and the model before you spec them):

• Vulcan eave round vents (8165-2192:0500)
• BrandGuard soffit and undereave vents (8165-2232:0500)
• Able Sheet Metal MGV soffit vents (8165-2363:0002)

Those records are ASTM E2886 / OSFM category 8165 listings. They are not a permit. They are not the soffit covering.

What people mix up

• Treating “the house is 12 feet tall” as a skip for every eave and deck.
• Measuring to the ridge instead of the opening or the framing.
• Putting 1/8 inch mesh on an ordinary eave louver that sits under 12 feet and calling it done.
• Treating perforated fiber-cement soffit as an ember-resistant eave vent. It is cladding. See Findings.
• Specifying an 8160 soffit panel and calling it a listed vent. 8160 is the covering. 8165 is the opening.
• Buying a listed gable vent and installing it on an eave underside without checking orientation. Read how to read a listing.
• Applying the eave-vent exception under an elevated deck.
• Treating IBHS Essential as already scoring enclosed eaves. That is Enhanced, and it is not a height rule.
• Importing this Oregon number onto a California job.

How to check

1. Confirm R327 is adopted for the lot. Start with the BCD wildfire page and the local department.
2. Measure from grade, or from the surface below, to each eave, soffit, and cornice opening. Write the height on the drawing.
3. Measure again to the lowest framing of that eave. If any portion is under 12 feet, you are in the underside-protection rule even if the vent is legal.
4. If you use exception 1, spec the model, not a brand name. Deschutes County accepts OSFM handbook products when they are shown on the drawings. Confirm the live GOVmotus record.
5. Walk gable, ridge, and crawlspace openings separately. Those still need mesh or a listed vent.
6. Do not apply the eave-vent exception under an elevated deck. Enclose to grade or protect that underside.
7. If the drawing claims unvented attic, there should be no attic ventilation openings on that drawing.

Limits

This page does not stamp your drawing. It does not pick a Craftsman rafter-tail detail. It does not rate airflow. Fine mesh and listed cores both cut net free area. Size attic ventilation so the house still meets R408 and R806 where those apply. FireApproved is not the building official. It does not make the house fireproof. R327, where adopted, is a new-construction code. IBHS is a designation. CWUIC is a different book.

Related records

• Ember-resistant vents, eaves, decking
• ASTM E2886, OSFM Building Materials Listing, SFM 12-7A-3
• Oregon R327 versus California CWUIC
• Mesh versus listed vents
• Unvented attic
• How to read a listing
• Show the product on the drawings
• Vented fiber-cement soffit is not an ember-rated vent