FireApproved
On this page
  1. Why it matters
  2. How the three strategies work
  3. The paths
  4. What people mix up
  5. How to check
  6. Limits
  7. Related records

Home / Guides / For builders — detailing / Bird blocks, boxed soffit, or unvented attic

Bird blocks, boxed soffit, or unvented attic

Last verified 2026-08-27.

Where Oregon R327 is adopted, the eave is a choice among three strategies, not a mandatory boxed soffit. You can keep exposed tails and put a manufactured ember- and flame-resistant vent in the bird-block opening. You can box the soffit on an R327.3.4.1 underside path. Or you can design an unvented attic so those attic openings do not exist (amendment PDF). Ordinary bird-block mesh is not the underside-vent exception. This page does not price the three.

You are looking up at the frieze. Either there are rectangular bird-block holes between the tails, a continuous soffit panel, or no attic vents at all. The inspector is asking which of those you drew.

The bird-block retrofit drawing (DET-012) is not published yet. Mesh scale lives on mesh versus listed vents. Exposed-tail geometry lives on Craftsman eaves. Do not use a house-level hub graphic as this chooser.

Why it matters

Embers enter the attic through holes in the eave. R327.3.2.1 blocks those openings on the underside unless the building official accepts a manufactured vent, or the opening is 12 feet or more above grade. The underside of the eave is a second job under R327.3.4.1 when framing is under 12 feet. A strategy that solves the hole and leaves the tails naked still fails the underside rule. The reverse is also true.

Deschutes County’s public FAQ lists three attic and crawlspace options. Unvented. Height. Or manufactured vents shown on the drawings. That FAQ is practice for those openings. It is not a price list.

How the three strategies work

StrategyWhat you are choosingWhat still has to be true
Keep exposed tails / bird-block swapA manufactured ember- and flame-resistant vent in the opening, plus an R327.3.4.1 underside pathOrdinary screen in the old bird block is not the exception. Net free area still has to meet R408 and R806
Box the soffitAn enclosed eave whose underside meets R327.3.4.1. Wall covering dies at the underside of that enclosurePerforated fiber-cement soffit is cladding, not an ember-resistant vent
Unvented atticNo attic ventilation openingsRemaining dryer, mechanical, gable, ridge, and crawlspace openings still need their own path. The eave as a projection still exists

IBHS Plus (the December 2025 technical standard; this site also calls that flame-and-radiant level Enhanced) wants eaves enclosed or protected on the exposed underside with noncombustible materials, a 1-hour rating, or 2-inch nominal lumber. That is a designation. It is not R327.

The paths

1. Bird-block swap (vented, exposed or with blocking). R327.3.2.1 Exception 1 is a vent manufactured to resist flame and burning embers. On this site those models live under vents in OSFM category 8165 / ASTM E2886. Put the model on the drawings. See show the product on the drawings. Exception 2 is an opening 12 feet or more that already meets R327.3.2 mesh or listed vent. See the 12-foot rule. The tails still need an underside path if framing is under 12 feet. Craftsman 4× tails are seminar practice, not a fifth numbered R327.3.4.1 item. Details live on Craftsman eaves.

Example listed eave and soffit vents (confirm the live listing and the model):

2. Boxed soffit. Enclose the eave. Protect the underside with noncombustible, ignition-resistant, 5/8 inch Type X behind the covering, a one-hour assembly, or ASTM E2957. Presenters at the 25 June 2026 seminar said enclosed soffit will require 5/8 inch gypsum on the soffit. Event testimony is not a BCD ruling. See Type X behind the covering. Vented fiber-cement soffit is not that vent. See the finding.

3. Unvented attic. Design the roof assembly so attic ventilation openings do not exist. That is a moisture and insulation design, not foam in a bird block. Deschutes lists it next to the height exception and manufactured vents. Remaining openings still need mesh or a listed vent. See unvented attic.

Do not mix the three on one attic without drawing which openings exist.

What people mix up

  • Leaving hardware-store bird-block screen and calling it R327.
  • Boxing the soffit with perforated fiber-cement and calling it an ember vent.
  • Treating unvented as tape or foam in the old holes.
  • Treating IBHS Plus enclosed eaves as an Oregon skip of R327.3.4.1.
  • Pricing the three from memory. This page does not.

How to check

  1. Confirm R327 is adopted for the lot.
  2. Look at the eave. Open tails, boxed soffit, or no attic vents.
  3. If there is a hole on the underside under 12 feet, find a manufactured ember- and flame-resistant vent on the drawing, not a brand name.
  4. If the soffit is boxed, name the R327.3.4.1 underside path.
  5. If the sheet says unvented, there should be no attic ventilation openings on that drawing.
  6. Size remaining vents so the house still meets R408 and R806 where those apply.

Limits

This page does not pick a Craftsman tail size. It does not rate airflow. It does not ship construction-cost figures. DET-012 is not published. FireApproved is not the building official. IBHS is a designation. R327, where adopted, is a new-construction code.

Questions

Can I keep the existing bird-block screen?

Not on an eave, soffit, or cornice underside under 12 feet, unless the building official accepts a manufactured ember- and flame-resistant vent. Ordinary bird-block mesh is not that exception. Openings 12 feet or more may use the R327.3.2 mesh path. Confirm the height and the product with the official.

If I box the soffit, can I skip Type X?

Boxing is not itself an underside path. R327.3.4.1 still wants noncombustible, ignition-resistant, Type X behind the covering, a one-hour assembly, or ASTM E2957, unless an exception applies. Presenters at the 25 June 2026 seminar treated enclosed soffits as a gypsum-on-the-soffit conversation. Event testimony is not a BCD ruling.

Does unvented attic finish the eave?

Unvented attic removes attic ventilation openings you do not have. The soffit still exists as a projection. Remaining dryer, mechanical, gable, ridge, and crawlspace openings still need their own path. Foam in an existing bird block is not an unvented attic.

Which of the three is cheapest?

This page does not ship prices. Headwaters cost figures are not opened here. Pick the path the adopted code and the official will stamp.

Sources