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Type X behind the covering
Where Oregon R327 is adopted, one layer of 5/8 inch Type X exterior gypsum sheathing behind the covering is a deemed-to-comply path on walls and on several undersides. It is not an ASTM E136 pass for the board you see. Presenters at the 25 June 2026 Central Oregon seminar said that path needs a firewall inspection after the gypsum is screwed on and before you cover it.
You are looking at a wall or a boxed soffit before the finish covering goes on. The inspector wants 5/8 inch Type X exterior gypsum sheathing, screws in, still visible. After you cover it, they cannot see the path.
Why it matters
Embers and heat collect at the wall, under the eave, and under porch ceilings. Wood siding and open tails are still common in Central Oregon. Type X is how many of those drawings keep the visible covering and still meet a numbered R327 path (amendment PDF). If you hide the gypsum before inspection, the official cannot verify the path you claimed.
Type X does not finish vents, gutters, or Zone 0. It does not make the house fireproof.
How it works
The code names a layer, not a brand of siding. On walls, R327.3.3 exception 1 is one layer of 5/8 inch Type X exterior gypsum sheathing, applied behind the exterior wall covering or cladding, on the exterior side of the framing. The covering can be wood. The gypsum is part of the assembly. It is not an E136 pass for the visible board. See ignition-resistant versus noncombustible.
The same 5/8 inch Type X-behind-covering recipe repeats on undersides. Eaves and soffits. Patio and porch ceilings. Cantilevered floor projections. Elevated-structure underfloors. Each section has its own trigger and its own siblings.
A 1-hour fire-resistance-rated exterior wall assembly is a separate option. R327 points at the Gypsum Association Fire Resistance and Sound Control Design Manual for those assemblies. Put the design number the project actually uses on the drawing. Do not invent a GA file number. This site did not open that manual for this page.
FEMA P-737 says enclosing overhangs and soffits with 5/8-inch Type X gypsum board typically meets a one-hour fire-resistance rating, and it prefers a flat horizontal soffit over a sloped one. That is FEMA best practice. It is not the Oregon wording.
Where the gypsum goes
| Location | Section | When Type X applies | Not this section |
|---|---|---|---|
| Exterior wall | R327.3.3 exception 1 | One layer of 5/8 inch Type X exterior gypsum sheathing behind the cladding, on the exterior side of the framing. No 12-foot skip for the wall covering. | Ignition-resistant or noncombustible covering, heavy timber, log, ASTM E2707, or a 1-hour exterior-wall assembly |
| Eaves, soffits, cornices | R327.3.4.1 item 3 | Any portion of the framing less than 12 feet above grade or the surface below. Type X behind the covering on the underside of rafter tails, truss tails, or soffit. | Height exception with 2-inch nominal eave fireblocking. Gable-end overhangs. Fascia and other architectural trim boards. See the 12-foot rule and Craftsman eaves. |
| Patio and porch ceilings | R327.3.4.2 item 3 | Greater than 200 square feet and less than 12 feet above grade. Type X behind the covering on the underside of the ceiling. | Architectural trim boards. Ceilings at or under 200 square feet are outside this section’s Type X trigger. |
| Cantilevered floor projections | R327.3.4.3 item 3 | Less than 12 feet above grade or the surface below. | Architectural trim boards. |
| Underfloor of elevated structures | R327.3.4.4 item 3 | Enclose to grade, or protect the underside. Type X behind the covering on the underside of the floor assembly. The code text states no 30-inch or 12-foot band here. | Heavy timber structural columns and beams. Walking-surface rules are R327.3.5, a different section. |
Siblings on the underside lists are noncombustible material, ignition-resistant material, the 1-hour assembly, or an ASTM E2957 tested underside. Type X is one numbered option. It is not the only option.
Wall covering termination. R327.3.3.1 runs the wall covering from the top of the foundation to the roof and terminates it at 2-inch nominal blocking at roof overhangs, or at the underside of an enclosed eave or soffit. Enclosing the eave does not skip the wall path.
Vents stay vents. If a soffit under 12 feet has a ventilation opening, R327.3.2.1 wants a manufactured ember- and flame-resistant vent the building official accepts, or an opening 12 feet up. Perforated soffit is not that vent. See vented fiber-cement soffit. An unvented attic is a different path. It removes attic openings. It is not Type X on the soffit.
The inspection. On 25 June 2026, City of Bend Building Safety and Deschutes County Community Development presented a firewall inspection when 5/8 inch Type X behind finish material is the chosen method. Schedule it after the gypsum is installed and screwed, and before the finish covering. That is event testimony. Confirm with the official. Spray-applied fire retardant is a different special-inspection conversation. Do not treat that as the Type X inspection.
Show the gypsum on the drawings. Deschutes County wants handbook products listed on the drawings when you use that list. Type X is a code recipe, not an OSFM listing ID. Still put the product and the section on the sheet. See show the product on the drawings.
What people mix up
- Using interior 1/2 inch drywall and calling it the R327 Type X path. The amendment names 5/8 inch Type X exterior gypsum sheathing.
- Reading Type X as an ASTM E136 pass for the visible siding. It is a deemed-to-comply assembly path.
- Inventing a Gypsum Association file number. The 1-hour path cites the manual. The design number is per project.
- Treating Type X as the only enclosed-soffit path. Presenters said an enclosed soffit will require 5/8 inch gypsum. That is seminar practice. R327.3.4.1 still lists five numbered paths.
- Writing the 30-inch to 12-foot walking-surface band onto R327.3.4.4. That band is R327.3.5 only. Underfloor is enclose-to-grade or protect, with no band in the code text. Seminar slides that mix the two are practice, not the amendment.
- Covering the gypsum before the firewall inspection.
- Painting a coating on wood siding instead of a numbered wall path. See coatings.
- Wrapping fascia because the soffit has Type X. Fascia is exempt. See the fascia finding.
- Treating an unvented attic, or a 4x exposed tail, as this page. Those are other guides.
- Importing a California “listed siding only” note onto an Oregon Type X drawing. CWUIC is a different book. See R327 versus CWUIC.
How to check
- Read the adopted code for the lot. If R327 is not adopted, this is voluntary hardening or an insurer checklist.
- Name the section. Wall, eave, porch ceiling, floor projection, or underfloor. The triggers differ.
- For eaves, porch ceilings, and floor projections, measure to the lowest framing, not the ridge.
- For porch ceilings, check area and height. Type X in R327.3.4.2 is for ceilings greater than 200 square feet and less than 12 feet above grade.
- Confirm the board. 5/8 inch. Type X. Exterior gypsum sheathing. One layer. Behind the covering. Exterior side of the framing on walls.
- Put that stack on the drawing. Do not hide it behind “per code.”
- If this is the path, schedule the firewall inspection before the finish covering. Confirm the hold point with the official.
- If you use the 1-hour assembly path instead, name the Gypsum Association design the project actually uses. Do not invent a number.
- Count remaining vents. Type X does not replace mesh or a manufactured ember-resistant vent on openings that still exist.
Limits
This page does not spec fasteners, joint treatment, or weather exposure. It does not host the Gypsum Association manual. It does not decide what Bend or Deschutes will stamp on a given job. Event testimony is dated 25 June 2026.
It does not replace the Craftsman eaves guide, the unvented attic guide, or the ignition-resistant versus noncombustible guide. The wall-stack drawing for Type X behind siding is not published yet. The soffit exhibit on this page is the closest passed detail.
FireApproved is not the authority having jurisdiction and not a listing body.
Related records
Questions
Can I keep wood siding if I put Type X behind it?
Where R327 is adopted, one layer of 5/8 inch Type X exterior gypsum sheathing on the exterior side of the framing, behind the cladding, is a deemed-to-comply wall path. The wood covering is still the covering. Type X is not an ASTM E136 pass for that board. Confirm the detail with the building official.
Is interior Type X drywall the same path?
No. The amendment names Type X exterior gypsum sheathing, 5/8 inch, one layer, behind the covering. Interior 1/2 inch drywall is not that product.
Do I have to enclose every eave with Type X?
No. Enclosure is one way to protect an underside. R327.3.4.1 still lists noncombustible covering, ignition-resistant covering, Type X behind the covering, a one-hour assembly, or an ASTM E2957 soffit. Exposed tails have their own guide. Fascia is exempt.
When is the firewall inspection?
Presenters at the 25 June 2026 Central Oregon seminar said a firewall inspection is required when 5/8 inch Type X behind the finish is the chosen method. Schedule it after the gypsum is installed and screwed, and before you cover it. That is event testimony from City of Bend Building Safety and Deschutes County Community Development. It is not a BCD ruling. Confirm with the official.